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Climate change and its associated symptoms, such as warming air temperatures, glacier retreat, reduced snowpack, and increased variability in precipitation, are warming rivers and lakes. Such warming water temperatures threaten cold-water fishes in some regions. For instance, warm water temperatures can kill or harm anadromous Pacific salmon as they migrate upstream to spawning grounds. In this study, we assessed how tributaries, and their relative watershed properties, shape temporal and spatial dynamics of temperatures during the summer months in a salmon migratory river. We focused on the mainstem of the Babine River of British Columbia, an important migratory corridor for steelhead and the five eastern Pacific salmon species, but particularly for sockeye salmon that spawn in stream reaches above the Babine Lake, at the river’s headwaters. We discovered that large glacier- and snowpack-fed tributaries cooled the Babine River by approximately 2 °C over its 96 km length. Different tributaries played different temperature functions. Cooler and more glacierized rivers were associated with a bigger change in temperature between upstream and downstream sites. Understanding how water temperatures change during adult salmon migration, especially within riverscapes on the edge of potentially harmful temperatures, can help inform proactive management options in a warming world.

Sea-run brown trout (Salmo trutta) have a highly phenotypically plastic life history that allows them to be effective colonizers and competitors in freshwater. This paper documents a previously unknown spawning behaviour in a brackish, tidally influenced estuary 14 km from the mouth of the Vosso River, a major Atlantic salmon- and sea-run brown trout–producing river in western Norway. Putative spawning gravel was observed, and sea-run brown trout deposited eggs that hatched in April. Survival of recruits was high (> 95%) in the tidal spawning gravel. These areas are strongly tidally influenced with a peak of 23.17 psu recorded at the lowest spawning ground. The observation of spawning so far from the river mouth may be unique in such a system with a long estuary but provides important insight into the biology of sea trout. Invasion of pink salmon, also known to spawn in estuaries, may negatively affect the competitive balance of sea trout with other salmonids in rivers where sea trout populations rely on recruitment from these relatively extreme spawning areas. Restoration of estuaries that have been modified by dredging or channelization may be important to ensure quality and heterogenous habitat for sea trout spawning given that haline spawning grounds could contribute to population resilience.

Many fish spawn in aggregations, but little is understood about the dynamics governing the success of spawning interactions. Here, we evaluate the influence that location of lek-like mating territories has on spawning interactions of Gomphosus varius. We used direct observations of spawning and egg predation events as well as local population counts to compare the rates of spawning, spawning interruptions, and predation on the eggs of G. varius at Finger Reef, Apra Harbor, Guam. We hypothesized that spawning rates would be highest among seaward locations that facilitate transport of pelagic larvae from reefs and that those territories would subsequently experience higher densities of egg predators, egg predation rates, and spawning interruptions. Male spawning success was highly skewed by mating territory location, with holders of the outer, seaward mating territories being more successful than those males holding territories in the middle and inner areas of the aggregation site. Within the outer territories, male mating success was also skewed by location. Egg predation was observed occasionally and increased linearly with bird wrasse spawning frequency. The population densities of egg predators were distributed equally across the study area. Spawning interruptions occurred most frequently within the inner zone of the spawning aggregation due to greater male-male aggression in intraspecific competition for females and territories. This study provides evidence that reef location influences the spawning success, egg predation rates, and spawning interruption rates of fishes that reproduce using lek-like mating territories.

Sockeye salmon that spawn downstream of rearing lakes are an important example of the challenges faced by organisms with complex life histories requiring connectivity in aquatic habitat complexes. Specifically, newly emerged juvenile sockeye salmon must migrate upstream, against the flow of water, if they are to reach lake rearing habitat. Here, we examine the spatial and temporal dynamics of the water velocity landscape and juvenile sockeye salmon movement and condition at increasing distances downstream from the lake outlet of an important sockeye salmon system, the Babine Lake of British Columbia, one of Canada’s largest and most important sockeye salmon rearing lakes. The results of this study indicate that (i) there were seasonal and spatial patterns of water velocities that exceed the ability of juveniles to swim upstream to lake rearing habitat, (ii) higher water discharge was associated with more velocity barriers and potentially with less upstream movement of juveniles, and (iii) juveniles rearing in the lake obtained larger sizes (30% longer and 150% heavier) than those in downstream river habitats. Multiple processes that may be influencing these patterns could include more abundant food resources, lower metabolic demands, or size-selective immigration, emigration, or mortality among habitats. Years and seasons with high discharge may temporarily create one-way, downstream transport routes at lake outlets. Long-term changes in hydrology, perhaps driven by climate variability or land-use change, may control the degree to which lake outlets function as bidirectional travel corridors or one-way travel routes for young sockeye salmon.

Nest construction by males is a common reproductive strategy in fishes, but little is known about intra-specific variation in nesting behavior and reproductive interactions with other species. In the southeastern USA, reproductive interactions between bluehead chub (Nocomis leptocephalus) and their nest associate, such as yellowfin shiner (Notropis lutipinnis), are mutualistic because the shiner requires chub nests to spawn but the chub also benefits from additional shiner eggs by reducing predation risk on their own eggs (i.e., dilution effect). As proxies for reproductive success of bluehead chub, we studied factors affecting their nest size variation and utilization by yellowfin shiner in three streams in the upper Piedmont region of South Carolina, USA. A total of 92 nests (71 spawned and 21 abandoned) were located, and we recorded spawning activity, nest size, number and size of male bluehead chub, number of yellowfin shiner, and environmental variables for 89 consecutive days in 2016. Path analysis showed that larger males spawned earlier in the season than smaller males, and instances of pebble re-use for nest construction increased through the spawning season, which extended from April to June. Larger males more likely shared the same nest with each other than smaller males, and larger or more males constructed larger nests and attracted more yellowfin shiner. Nest size also increased when males re-used substrate materials from old nests, and nests built in this manner (36 nests) were equally prevalent as newly constructed nests (35 nests). This study suggests that complex mechanisms mediate host nest size and interactions with nest associates, and individual variation likely shapes dynamics of the mutualistic reproductive interaction.

Populations of wild spring-run Chinook salmon in California’s Central Valley, once numbering in the millions, have dramatically declined to record low numbers. Dam construction, habitat degradation, and altered flow regimes have all contributed to depress populations, which currently persist in only a few tributaries to the Sacramento River. Mill Creek (Tehama County) continues to support these threatened fish, and contains some of the most pristine spawning and rearing habitat available in the Central Valley. Despite this pristine habitat, the number of Chinook salmon returning to spawn has declined to record low numbers, likely due to poor outmigration survival rates. From 2013 to 2017, 334 smolts were captured and acoustic tagged while out-migrating from Mill Creek, allowing for movement and survival rates to be tracked over 250 km through the Sacramento River. During this study California experienced both a historic drought and record rainfall, resulting in dramatic fluctuations in year-to-year river flow and water temperature. Cumulative survival of tagged smolts from Mill Creek through the Sacramento River was 9.5% (±1.6) during the study, with relatively low survival during historic drought conditions in 2015 (4.9% ± 1.6) followed by increased survival during high flows in 2017 (42.3% ± 9.1). Survival in Mill Creek and the Sacramento River was modeled over a range of flow values, which indicated that higher flows in each region result in increased survival rates. Survival estimates gathered in this study can help focus management and restoration actions over a relatively long migration corridor to specific regions of low survival, and provide guidance for management actions in the Sacramento River aimed at restoring populations of threatened Central Valley spring-run Chinook salmon.

The Green Sturgeon is a long-lived anadromous fish known to spawn in only three locations. Southern Distinct Population Segment (DPS) Green Sturgeon spawn only in the Sacramento drainage, while the Northern DPS spawns in the Klamath and Rogue rivers. In 2011, a young of year (YOY) Green Sturgeon was captured in the Columbia River below Bonneville Dam, providing preliminary evidence of a fourth spawning location. In 2017, four additional Green Sturgeon YOY of similar size were captured in the Columbia River below Bonneville Dam. Genetic analysis of all YOY samples indicates that they belong to the Northern DPS, confirming that the Northern DPS actually spawns in at least three locations. The detection of Green Sturgeon spawning in the Columbia River only in years with relatively high spring flow (2011, 2017), combined with confirmed correlations between flow and spawning for other White and Green Sturgeon populations, suggests that appropriate spawning conditions may only exist above a specific flow threshold. The Columbia River has the potential to play an important role in Green Sturgeon climate change adaptation due to its location at the northernmost end of the species’ reproductive range. We recommend future research to better quantify Green Sturgeon recruitment magnitude, frequency and dynamics in the Columbia River.

Spatial variation in habitat structure is a well-recognized characteristic of lotic ecosystems. The resulting patchwork mosaic provides opportunities for growth and survival as well as mortality risks for fish migrating through these systems. Dam construction within a watershed has numerous downstream tail water effects that alter creation and evolution of habitat features used by anadromous fishes that spawn and rear in these reaches. California Central Valley Pacific salmon (Oncorhynchus spp) are largely restricted to areas below impassable dams and these populations are undergoing widespread declines. High mortality of juvenile salmon in these reaches is thought to be a limitation to recovery. We conducted a radio telemetry study to evaluate spatial variation in juvenile Chinook Salmon (O. tschawytscha) survival and survival-environment relationships in three reaches of a Central Valley tail water. Additionally, we used mobile surveys to identify the location of last known detections to elucidate areas of disproportionate mortality. Our results indicated variation in flow and salmon size had greater explanatory power than year effects. However, relationships between flow, salmon size and survival were reach-specific indicating drivers of survival are spatially heterogeneous. Significant clumping of last known detections in the two lower reaches of the river suggests that mortality may be more frequent in these locations. Our results suggest that there is substantial spatial variation in migration mortality and both environmental conditions (flow) and salmon characteristics (size) have a strong influence on observed mortality. This information should be used to target actions that can support Chinook Salmon recovery.

Lake charr Salvelinus namaycush are endemic to the formerly glaciated regions of North America and spawn primarily in lakes, unlike most other Salmoninae. Spawning habitats for lake charr are thought to be characterized by relatively large substrate particle sizes which provide sufficient interstitial spaces for egg incubation, but little is known about the physical processes that create or maintain suitable habitats. We review the literature on lake charr spawning habitat and present a conceptual framework that examines the roles of physical variables in creating the appropriate conditions for egg incubation. A critical underlying assumption of this framework is that lake charr will select spawning habitats that provide suitable hypolentic flows for egg incubation. We suggest that the characterization of lakebed surface roughness, current patterns, substrate particle size, and groundwater flows at multiple spatial scales may yield significant insight into the physical mechanisms supporting lacustrine spawning habitats for lake charr and will be useful in creating predictive models of these habitats. This framework may also apply to other lake-spawning lithophilic fish species.

The Persimmon Eelpout (Eucryphycus californicus) is a relatively unknown, deep-sea fish inhabiting temperate marine waters on the west coast of North America. Using samples collected in the mid-1970s, the most recent targeted sampling for this species, we present basic life history attributes, and an analysis of the relationship between E. californicus and drift macrophyte habitat in the Monterey Canyon, California, USA. A diet analysis revealed that the fish consumes predominantly small crustaceans, especially amphipods and copepods, including species that associate with drift macrophyte habitat. Otoliths were analyzed to yield age estimates ranging from 0 to 6 years, and growth was modeled showing a maximum length of 203 mm for males and 271 mm for females. An analysis of the reproductive ecology of E. californicus showed that like many deep-sea fishes, females lay relatively few, large eggs. The species exhibits a protracted spawning period, and females spawn with only one functional ovary. Empirical information presented in this paper and anecdotal evidence shows that E. californicus likely relies on drift algae and seagrasses, a habitat subsidy exported to the deep-sea environment from adjacent kelp forest ecosystems, for shelter and to concentrate food resources. This example of a species dependent on an ecosystem subsidy adds to our knowledge regarding the effects of cross-ecosystem connectivity in the marine environment, and furthers our understanding of the ecology of the deep-sea macrofaunal assemblage in Monterey Bay.

For species of fish that spawn over a large geographic range, it is expected that populations will experience different water temperatures during early development. To gain a better understanding of water temperature regimes experienced by embryo and larvae among populations, we surveyed surface and intragravel temperatures at 10 locations where Coho Salmon (Oncorhynchus kisutch) spawn across British Columbia from mid-November to May. We chose coastal systems and interior systems at southern and northern latitudes to represent the range of potential conditions where fish spawn. Intragravel water temperatures varied significantly across study sites and were also significantly warmer than surface water temperatures – particularly during the coldest winter months. Northern interior populations experienced temperatures below 1 °C early in embryo development; less than a month after spawning and with fewer than 50 accumulated thermal units in some locations. Throughout the experimental period, temperature variability was less in intragravel water than surface water, but differences also existed among locations. Daily fluctuations in temperature were greatest for the southern-most coastal locations. Our results represent important findings when attempting to extrapolate incubation temperature from surface water temperature since even small differences in temperature have a cumulative effect in embryo and larval development.

Bonefish are typically thought of as ‘flats fish’ that reside in shallow, tropical and subtropical nearshore coastal waters. However, evidence from tagging and acoustic tracking studies indicate that bonefish migrate to staging areas, form large aggregations (>5000 individuals), and then move to deep-water drop-offs at dusk to spawn. Because the offshore spawning occurs under the cover of darkness, visual observations of the actual bonefish spawning events are not possible. Fortunately, behaviors during pre-spawning aggregations provide clues related to putative spawning bouts. For multiple locations in The Bahamas, we report on repeatable, predictable behaviors of bonefish in large prespawning aggregations. Just prior to moving from shallow to deeper waters, bonefish are observed breaking the water surface (‘porpoising’) and then returning to the aggregation. Bubbles are then observed emerging from the swirling aggregation; potentially gas being released from the bonefish. Ventral nudging, when one fish rubs its snout on the ventral region of another, has also been observed, but not as consistently as porpoising. Based on the depth profile of acoustically tagged fish, we hypothesize that porpoising is related to ‘pneumatic assist’ for egg release during spawning bouts. Although these observations provide circumstantial evidence that these behaviors are related to spawning, they are consistent with the prespawning behaviors of other marine fish that broadcast spawn. More research is needed to actually document a spawning bout; however, these clues in addition to other traits may be enough to encourage conservation measures to protect this important life history event for bonefish.

Este artículo contiene 15 páginas, 8 figuras, 4 tablas., Many grouper (Epinephelidae) species aggregate to spawn at specific times of year, at consistent locations, and at specific times of day and phases of the moon. The tiger grouper (Mycteroperca tigris) iswidely distributed in the Caribbean Sea and aggregates to spawn just after the full moon. In January and February 2003–2005, we conducted visual surveys of a tiger grouper spawning aggregation at Glover’s Reef, Belize. The primary objectives of this study were to describe grouper spawning activities with respect to the timing of the lunar cycle, identify and describe male and female spawning behaviors, and estimate the number of grouper spawning events each day. The peak number of both male and female tiger groupers counted each year occurred from 6 to 10 d after the fullmoon. The peak count of males was 1.6–2.2 times greater than the peak count of females. Six categories of male–male and six categories of male–female interactions were identified. All male tiger groupers displayed an ability to rapidly change color; this was often triggered by a close encounter with other male or female tiger groupers. The daily spawning activity was remarkably predictable. The first spawning occurred on average 8.1 min before sunset, and the last occurred 5.1 min after sunset. On average, less than half of the females at the spawning site spawned each day, but some females spawned more than once in a given day. Females appeared to choose their mates.

Many species of tropical marine fish aggregate to spawn, and the dynamics of these aggregations make them especially susceptible to overfishing and habitat loss. Spawning aggregations tend to attract reproductive adults from a large geographic area, sites are traditionally used across generations, and larval dispersal can help supply regional fish stocks. Thus, anthropogenic impacts to spawning sites can have population-level consequences over local and regional scales. A critical component in the challenge to conservation of aggregation-spawning species is identification and subsequent protection of spawning sites. Here we summarize fieldwork conducted to create a protocol for identification of pre-spawning aggregation sites for bonefish, Albula vulpes, in The Bahamas. The mixed-methods, field-based protocol includes Traditional Ecological Knowledge, assessment of spawning readiness, tracking using acoustic telemetry, behavioral observations, and mark-recapture, that combined meet the requirements for identifying pre-spawning aggregation sites. Pre-spawning site identification, in conjunction with information on other life stages and habitats, is essential for successful spatial management strategies. Since bonefish and many other tropical fishes that form spawning aggregation are ‘data poor’ and occur in regions where enforcement of fishery regulations is lacking, spatial management is often the best conservation strategy. This protocol builds upon similar previous efforts to identify spawning sites for groupers and snappers, and will contribute to information needs for conservation is an essential component in the conservation of aggregation-forming species such as bonefish across broad spatial scales.

Patagonian toothfish Dissostichus eleginoides Smitt 1898, is an important commercially targeted Notothenioid species in South-Atlantic waters. In this study we aimed to clarify several aspects of reproductive biology of Patagonian toothfish in the Falkland Islands waters. Histological examination of female gonads indicates that with the beginning of maturation females maintain at least two populations of oocytes, suggesting that toothfish requires up to two years for oocytes development. Females become mature at an average size of 79.1 cm indicating a decrease of first maturity size if toothfish females in the Falkland Island waters. The majority of females spawn at the size from 101 to 130 cm total length. Distribution of reproductive phases shows an increase of females at developing stage in December and March prior to the spawning peaks in May and August respectively. However, the majority of the toothfish population consist of non-spawning individuals remaining in regressing phase (55.8 to 85.6%) including the spawning period. The skip-spawning for toothfish has been defined as reabsorbing non-reproductive and resting types. The abbreviation of oocytes development in the gonads was observed from 1 to 22.1% of females which omitted the spawning season. Most likely females which remain in the spawning area have the opportunity to spawn more often, whereas females which undergo foraging migration toward Northern parts of the Falklands waters return to the spawning ground less often. Females remain Northern area longer to accumulate necessary amount of energy. This hypnotise is supported by the presence of females in immature, developing and regressing phase throughout surrounding Falkland Islands waters. Presence of post-spawning females in regressing stage throughout the Falklands waters suggest that toothfish may undertake irregular spawning/foraging migration when favourable for spawning condition occur.

Passive acoustic monitoring (PAM) of fish sounds has been used as a means of detecting the presence and abundance of fishes. Prior to PAM, bioacoustical analyses of sounds are needed to characterize species-specific characteristics of calls. With hydrophones placed in outdoor ponds, we recorded the mating calls of three species of prochilodontid fishes (Prochilodus argenteus, P. costatus, P. lineatus). Fish were induced to spawn and call by injection of carp (Cyprinus carpio) pituitary gland extract. We recorded a total of 394 pulse train calls and additional single pulse calls that were not associated with trains. The trains of all three species were similar in nature - series of low frequency pulses that lasted from 1 to 11 s, often with an initial rapid rise followed by a slow tapering of pulse amplitude. Dominant frequency of single pulses and trains was greatest in P. lineatus, with P. costatus and P. argenteus exhibiting lower single pulse dominant frequencies, and P. costatus having lower train dominant frequency. With data from the three species combined, the dominant frequency of pulses significantly increased with fish standard length. There was also a significant linear relationship between the dominant frequency of pulses and trains. Discriminant function analysis showed that differences in train dominant frequency, pulse duration, and pulse period between the three species were significant enough to discriminate between them. This study was the first to fully characterize the sounds of these three Prochilodus species, and should assist fisheries biologists monitoring spawning behavior in these species.

The potential effects of global warming on the allis shad population were tested by combining a time series of spawning acts with expected thermal survival rates for embryos and larvae until 14 days post hatching. The yearly mean survival of spawn for each reproductive season was calculated and an index of reproductive efficiency based on this survival rate was proposed. The randomness of the spawning tactics was evaluated by shuffling the spawn acts time series. This approach was applied to the Gironde-Garonne-Dordogne (south-west France) population, which recently collapsed. The yearly mean thermal survival of spawn is slightly variable at approximately 55% over 2003–2012 despite fluctuating temperatures. An especially low survival (35%) was recorded for the last season (2013). For eight of the 11 reproductive seasons, the index of reproductive efficiency was high (> 80%) and largely above indices obtained by a random spawning tactic. Therefore shad are able to adopt an efficient spawning tactic to anticipate favourable thermal conditions for survival of their offspring. However, thermal behavioural rules still need to be expanded to understand the failures in their reproduction efficiency.

The ayu (Plecoglossus altivelis) is an annual, amphidromous, plecoglossid fish, distributed in Vietnam, China, Taiwan, Korea, and Japan. To date, ayu have been found only in two rivers in northern Vietnam, where little is known about their life history. The Tien Yen River is believed to be the most southwestern habitat for this species. To determine whether newly hatched ayu larvae drift and to understand their downstream migration, intensive surveys were conducted in the Tien Yen River from October to March of 2013–2016. In total, 529 drifting ayu larvae were collected from four of six sampling stations along the river. Thus, ayu reproduction has been confirmed in this river for the first time, where only adult fish had been found previously. However, we did not successfully collect larvae in the eastern branch of the river, which has a hydroelectric dam, suggesting that ayu do not inhabit this branch or else do not reproduce there. The presence of drifting larvae in the western branch from mid-December to late January implies that they spawn from late November to mid-January. Drifting larvae were captured primarily at night, but peak occurrences varied depending upon the day and the sampling station. With the range of body sizes and variable diel abundance patterns, ayu in the Tien Yen River probably employ multiple spawning grounds. This study provides fundamental life history data for the vulnerable ayu populations in northern Vietnam.

Management and restoration planning for Pacific salmon is often characterized by efforts at broad multi-basin scales. However, finer-scale genetic and phenotypic variability may be present within individual basins and can be overlooked in such efforts, even though it may be a critical component for long-term viability. Here, we investigate Chinook salmon (Oncorhynchus tshawytscha) within the Siletz River, a small coastal watershed in Oregon, USA. Adult Chinook salmon were genotyped using neutral microsatellite markers, single nucleotide polymorphisms and “adaptive” loci, associated with temporal variation in migratory behavior in many salmon populations, to investigate genetic diversity based upon both spatial and temporal variation in migratory and reproductive behavior. Results from all three marker types identified two genetically distinct populations in the basin, corresponding to early returning fish that spawn above a waterfall, a spring-run population, and later returning fish spawning below the waterfall, a fall-run population. This finding is an important consideration for management of the species, as spring-run populations generally only have been recognized in large watersheds, and highlights the need to evaluate population structure of salmon within smaller watersheds, and thereby increase the probability of successful conservation of salmon species.

We studied the reproductive biology of Astyanax lacustris in the southern Pantanal, Brazil. A total of 382 fish were analyzed from February 2009 to January 2011. The sex ratio differed significantly from 1:1, with a larger proportion of females (χ2 = 27.24; p

Green Sturgeon (Acipenser medirostris) and White Sturgeon (A. transmontanus) are closely related species inhabiting the San Francisco Estuary (SFE) and Sacramento River. Both spawn in the Sacramento River. White Sturgeon typically remain within SFE throughout their lives while subadult and adult Green Sturgeon make marine migrations. These broad-scale patterns are known. However, the reach-specific timing of spawning migrations is not, and little is known about seasonal movements of juveniles and subadults. We tagged 41 Green and 160 White Sturgeon with acoustic transmitters (2010–2012). Analyses also included 167 previously tagged sturgeon. Over 300 receivers deployed throughout the Sacramento River, SFE, and nearshore Pacific Coast detected movements. Adult Green Sturgeon moved quickly though SFE to their spawning reach, using the mainstem through the Delta. 5% of spawning Green Sturgeon remained on the spawning reach for over 300 days. White Sturgeon spent significantly less time in their spawning reach before exiting (32 ± 48.2 days vs. 197 ± 97.3 days) and instead selected northern Delta sloughs over the mainstem for pre-spawning migrations. Even at earlier life stages, Green Sturgeon had more marine distributions than White Sturgeon. Juveniles and subadults of both species moved between the San Francisco Bay and Delta throughout the year, but only White Sturgeon overwintered in the Delta. Additionally, we refine several life history parameters for sturgeon in California. We provide a comprehensive characterization of Green and White Sturgeon movements within the SFE and Sacramento River across life stages. These analyses will inform reach-specific management of each species.

Body size at release for hatchery-reared steelhead is positively correlated with probability of survival to return as an adult. Although the relationship between body size and survival is well documented, little is known about what factors influence growth in the hatchery at the family level. We test if parent length, parent type (hatchery or natural), parent run date, or date of spawning correlate with among-family variation in offspring growth in the hatchery. Using Hood River winter steelhead (Oncorhynchus mykiss), two experiments were performed over two brood years. No effect of father length, parental type, or parental run date was found on offspring length in either year. Mother length was positively correlated with offspring length during both brood years and egg size data suggest this result occurs because longer females have larger eggs (i.e., it is a maternal effect). Although run date of parents was not correlated with offspring size, the date of spawning was negatively correlated with offspring size in a year with a protracted spawning season. Families spawned later in the season were smaller than those spawned earlier even though all fish began feeding on the same date. The spawn date effect lasted surprisingly long, being correlated with offspring size one year after spawning. A possible explanation for the spawn date effect is that eggs from early-spawned families were reared in chilled water to slow development so all families would begin feeding on the same date (a common hatchery practice). Colder water could have reduced metabolic costs and provided a surplus of energy to be used for somatic growth. This study highlights a little-studied environmental effect that could have large effects on long-term growth rates for hatchery-reared O. mykiss.

Numerous life histories have been documented for bull trout Salvelinus confluentus. Lacustrine-adfluvial bull trout populations that occupy small, headwater lake ecosystems and migrate short distances to natal tributaries to spawn are likely common; however, much of the research on potamodromous bull trout has focused on describing the spawning and rearing characteristics of bull trout populations that occupy large rivers and lakes and make long distance spawning migrations to natal headwater streams. This study describes the spawning and rearing characteristics of lacustrine-adfluvial bull trout in the Quartz Lake drainage, Glacier National Park, USA, a small headwater lake ecosystem. Many spawning and rearing characteristics of bull trout in the Quartz Lake drainage are similar to potamodromous bull trout that migrate long distances. For example, subadult bull trout distribution was positively associated with slow-water habitat unit types and maximum wetted width, and negatively associated with increased stream gradient. Bull trout spawning also occurred when water temperatures were between 5 and 9 °C, and redds were generally located in stream segments with low stream gradient and abundant gravel and cobble substrates. However, this study also elucidated characteristics of bull trout biology that are not well documented in the literature, but may be relatively widespread and have important implications regarding general characteristics of bull trout ecology, use of available habitat by bull trout, and persistence of lacustrine-adfluvial bull trout in small headwater lake ecosystems.

This is the first report on the fecundity in adults of two nonparasitic lamprey species at risk, the Vulnerable Kern Brook Lamprey, Lampetra hubbsi and the Critically Endangered Macedonia Brook Lamprey, Eudontomyzon hellenicus. The mean absolute fecundity of L. hubbsi was 1865 eggs and that of E. hellenicus was 994. The higher fecundity in L. hubbsi was directly related to its higher mean gonadal mass (0.90 g) relative to that in E. hellenicus (0.52 g). Based on preserved museum material possessing well-developed primary and secondary sexual characters, the spawning period for L. hubbsi was inferred to be February-March and for E. hellenicus to either extend from January to May or to occur as separate events; one in January and the other in May. Because metamorphosing ammocoetes of E. hellenicus have been collected in October and in January, it is hypothesized that those metamorphosing in October spawn in January and those metamorphosing in January spawn in May. These periods need to be corroborated with field observations. Evidence for E. hellenicus spawning in January is based on the presence of spent females of this species collected in that month.

Development on Grand Bahama in the Bahamian Archipelago during the 1950’s to 1970’s resulted in substantial changes to the island’s geography. Hawksbill Creek, which potentially served as a natural migration route for fish from the north side to the south side of the island, was severed and replaced by a man-made canal called the Grand Lucayan Waterway (GLW). Bonefish (Albula spp.), a sport-fish that contributes more than $141 million to the Bahamian economy annually, is one such species that may have been affected. The purpose of this study was to determine contemporary movement corridors of adult bonefish during their spawning season (October to May) in Grand Bahamian waters. This was accomplished by using a passive acoustic telemetry array of 17 receivers and 30 transmitter-implanted individuals. A total of 26,108 detections were logged from 20 of the fish. Eight bonefish tagged on the north side used the GLW to access waters on the south, whereas no transmitter-implanted fish tagged on the south side fully traversed the man-made canal, suggesting that primary spawning areas may be located on the south side of the island. This result is consistent with previous reports that bonefish spawn near deep water which is easier to access on the south side of Grand Bahama. Further supporting this finding, two other bonefish tagged on the north side forayed around the east end of the island and were detected on receivers approximately 88 km from their tagging locations. Additionally, two other bonefish tagged on the north side were detected at the west end of the island, with one individual continuing its movements along the south side of the island for an approximate straight-line distance of 80 km. Canal use typically corresponded to days immediately prior to or after new or full moons, indicating that movements were related to spawning. This study suggests that despite historical habitat modifications, bonefish today use the GLW as a movement corridor for migrations during spawning season, emphasizing the importance of protecting the canal from any activities that could impede connectivity.

The purpose of this study was to identify spawning habitat, determine home ranges, and examine movement patterns for a naturally reproducing population of Great Lakes muskellunge in the lower Antrim County chain of lakes, Michigan. Muskellunge spawning sites were identified by tracking of implanted muskellunge using a directional hydrophone and by nighttime spotlight surveys. All spawning fish tagged in Torch or Clam Lake spawned in Clam Lake, while most spawning fish tagged in Elk or Skegemog Lake spawned in the Torch River; one appeared to spawn in Lake Skegemog. Of the 32 potential spawning sites, 28 (87.5 %) contained submerged aquatic vegetation as the dominant habitat type, while the remaining 4 sites were divided equally between woody debris (6.25 %) and bare substrate. All but one implanted muskellunge returned from spawning sites to the same lake in which they were captured and implanted. Of the 24 tagged muskellunge, four were harvested via angling or spearing within 1 year after tagging, and two additional fish were assumed harvested when contact was lost. Implanted muskellunge tended to remain in the lakes during the winter, then move into spawning areas in spring, eventually returning to open lake sites where they resided over summer. Muskellunge movement behavior diverged after spawning each year, with 11 tagged fish (61.1 %) remaining in Skegemog or Clam Lake for the summer, and seven individuals traveling to Elk or Torch Lake. Muskellunge home ranges averaged 612 ha and ranged from 17 to 5,287 ha.

Accurate descriptions of reproductive profiles are important for effective conservation and stock assessment efforts. We examined the reproductive traits of an Okinawan population of western Pacific gizzard shad (Nematalosa come) using histological analyses. The observed lengths at 50 % maturity were approximately 180 mm standard length (SL) for females and 130 mm SL for males, which corresponded to 4-year-old fish for females and at least 2-year-old fish for males. The spawning season was estimated to occur from January to August, peaking from March to June, with active spawning occurring during an increase in seawater temperature. The lipidosomatic index of both sexes decreased until June, presumably as the fish expended energy to spawn. The fecundity (F) of females, tested using 62 ovaries, was related to SL: F = 3.471 × 10−2 × SL3.122. The Okinawan population of N. come had a longer spawning season and a higher fecundity than other populations for which these data are available. Such favorable traits may contribute to the persistence of this population at the species’ distributional margin. Our findings indicate that the spawning seasons of Okinawan populations of N. come and Nematalosa japonica overlapped, implying that hybrid production occurs under natural conditions. Around Okinawa Island, however, the extent of shallow waters is rapidly decreasing because of recent land reclamation. We suggest the diminution of suitable sites as a possible factor for narrowing spawning opportunities and promoting the recent appearance of natural hybrids. Shallow habitats should be conserved to preserve healthy populations of the species.

We used radio telemetry to investigate the freshwater biology of adult Pacific lampreys in the Smith River, a coastal Oregon watershed. We tagged 91 adults at a fish ladder trap (65 km from the ocean) in the spring of 2006–07 and 2009–10. We did not detect a radio-tagging effect on short-term survival and migration rate relative to a PIT-tagged cohort. Fish began migrating April–June and averaged 8.5 km/d. Most were holding by late June, which coincided with the onset of base flow and peak water temperatures. Summer holding locations were distributed 68–146 km from the ocean. Migration distance was inversely related to tagging date but was not related to fish length. Holding fish were strongly associated with glides and boulders as cover. Fish held for about 9 months prior to spawning, although 75 % made at least one upstream movement in winter coincident with high-water events. Individuals began their final migration/spawning phase in March and April, coinciding with increasing temperature and discharge, and were highly vulnerable to predation. Fish that were tagged during the initial migration and held in the upper basin mainly moved downstream to spawn, whereas fish that were tagged during the final migration moved upstream prior to spawning. Some spawned in multiple locations, separated by ≤16 km, and with 1–3 other spawners. The broad distribution of holding and spawning habitat of this population and the diverse needs of individuals suggest that conservation of coastal lamprey populations will require protection and restoration at the watershed level.

We used acoustic telemetry to study the post-spawn movement of Oncorhynchus mykiss kelts released in April 2005 and 2006 from the Coleman National Fish Hatchery, Anderson, CA. Following release, O. mykiss kelts demonstrated both anadro- mous and non-anadromous life histories, with some fish alternating life history strategies between years. Anadromy was most common, characterized by a short-term residence near the release site, followed by sustained downstream emigration once initiated. O. mykiss kelts demonstrating anadromy arrived at the Golden Gate Bridge from April to mid-July. Repeat spawning migrations of anadromous O. mykiss kelts began from late-September through October of the year of release. High fidelity back to Battle Creek was ob- served, occurring from late-September through Novem- ber. While most O. mykiss kelts were anadromous, at least 10 % remained in freshwater, or residualized. O. mykiss kelts that residualized demonstrated two distinct patterns of movement: 1) residency near the release location, and 2) potamodromy. Overall survival was high with 36 % and 48 % of O. mykiss kelts released making a repeat spawning migration and demonstrating iteroparity in 2005 and 2006, respectively. Increase in body lengths of O. mykiss kelts that returned to the Coleman NFH were significantly greater for anadro- mous fish, compared to fish that residualized, but sur- vival was higher for fish that residualized. Release of hatchery O. mykiss kelts could result in both positive and negative genetic and ecological effects to hatchery- and naturally-producing salmonids. We believe the ben- efits of releasing O. mykiss kelts at the Coleman NFH, including increased numbers and size of fish in the recreational fishery and genetic and demographic bene- fitstothe hatcherybrood stock outweighthe limitedrisk to natural populations that would result from predation and competition of the relatively small number of O. mykiss kelts that resided in fresh water.

We studied the efficacy of the process for capture and upstream relocation of 26 adult spring-run Chinook salmon in Butte Creek, California in 2009. These fish had ceased volitional upstream migration prior to reaching their summer holding habitat. The purpose of the relocation was to move fish upstream of two water diversion dams and release them in a part of the stream from which they could presumably swim to cool summer holding habitat, then spawn in the fall. Fish were netted, transported by truck, given an esophageal radio tag/temperature tag, and released. Radio tagging proved to be a useful technique for determining the survival and movement of relocated fish and temperature tags provide useful information to determine thermal exposure and time of death. Twenty-three tags (88 %) were recovered, compared with a 10 % tag recovery rate for an earlier study using fin clips. Most tags were recovered within 3.5 km upstream and 1 km downstream of the release site. A single tag was recovered 6 km upstream. No fish were determined to have survived to spawn. Temperature tag data indicate that most of the salmon died within 2–6 days after the relocation operation. After preventative measures have been exhausted, future relocations efforts, in any setting, should consider (1) intervention as soon as fish cease volitional migration but before they are exposed to further deleterious conditions (2) monitoring environmental conditions to choose appropriate release sites (3) evaluation of disease transmission risk, and (4) handling practices that minimize potential stress due to air immersion and thermal shock.

Patterns in the timing of spawning of the eastern Australian river garfish Hyporhamphus regularis ardelio were investigated by sampling fish throughout 24 h during their peak spawning period. Patterns in gonadosomatic indices, the presence of hydrated oocytes and post-ovulatory follicles in histological ovary sections, together with previously demonstrated polymodal distributions of oocytes undergoing final maturation, indicated that river garfish were capable of spawning at any time during the 24 h period. Spawning had either recently occurred or was imminent in all females sampled suggesting that river garfish could spawn multiple times in a given season. Although energy resources are used in the production of low numbers (

Atlantic sturgeon migrate between ocean and freshwater habitats to spawn, and juveniles spend several years in fresh/brackish water before returning to the ocean. Because strontium/calcium (Sr/Ca) ratios are diagnostic for freshwater and marine environments, we examined the utility of energy-dispersive x-ray fluorescence (EDXRF) to quantify Sr/Ca ratios of Atlantic sturgeon pectoral fin spines. Atlantic sturgeon spines from wild adults and experimental juveniles were analyzed along a linear transect from the primordium to the outermost point. To verify the technique hatchery juvenile Atlantic sturgeon were held in experimental tanks at

Across many fish species, large females tend to exhibit higher individual reproductive success due to elevated fecundity and the provisioning of better conditioned eggs and offspring compared to small females. By contrast, effects of paternal body size on reproductive success are less well understood. We disentangled the maternal- and paternal-size dependent effects on reproductive output and early life history in zebrafish (Danio rerio). In the laboratory, females and males from four size categories (small, medium-sized, large and very large) were allowed to spawn freely in a full factorial design with 10 replicates per size combination. As expected, larger females produced more eggs and better conditioned offspring compared to smaller females. Male body size further contributed to zebrafish reproductive success: offspring sired by large males exhibited higher hatching probability and these offspring also hatched earlier and larger than offspring fertilized by small males. However, the largest males experienced lower mating success and received fewer eggs than males of the smaller size classes. While male body size substantially affected reproductive success in zebrafish, it remained unclear whether and to what degree direct paternal effects (e.g., related to sperm quality) or indirect paternal effects stemming from differential allocation patterns by females were the mechanism behind our findings. Answering this question constitutes an important future research topic.

Various aspects of the reproductive biology of two archer fishes Toxotes chatareus and Toxotes jaculatrix were studied to describe gonad development, spawning season, sex ratio, and fecundity. Spawning season was assessed using monthly changes in gonadosomatic index (GSI) and histological inspection of the gonads. Both species exhibit two modes of oocytes; a mode of small primary growth oocytes and a single mode that increases with size as oocytes sequester vitellogenin and undergo maturation, showing the synchronous oocyte development typical of total spawners. Based on GSI values and advanced stages of oocyte maturity, T. chatareus and T. jaculatrix, females appear to spawn from November to December. The average fecundity of female T. chatareus was 55 000 ± 5538 eggs, and T. jaculatrix was 50 000 ± 3440 eggs; fecundity ranged from 20 000 to 150 000 eggs for both species, with relative fecundities of 600 to 1100 eggs/g body weight, and a mean value of 800 ± 32 for T. chatareus; relative fecundity ranged from 500 to 1100 with a mean value of 700 ± 23 for T. jaculatrix. Sex ratio, defined as the proportion of males to females, was 2.2 and 2.5 in T. chatareus and T. jaculatrix, respectively. The apparent abundance of males in samples could be due to females being positioned lower in the water column and therefore being sampled less frequently. Our results indicate that in both species, spawning occurs between the months of November and December during the monsoon season, which provides the mangrove coastal waters inhabited by these species with an abundance of food resources and additional floodplain nursery habitat for larvae and juveniles.

Many species of fishes along the east coast of the United States have complex life histories, especially those that move over hundreds of kilometers across ocean and estuarine habitats. To further unravel the life history of one of these, the speckled worm eel, Myrophis punctatus we examined samples from extensive time series and discrete samples collected in the ocean and estuaries between Florida and Massachusetts. We now surmise spawning occurs between fall and early winter in the ocean south of Cape Hatteras, North Carolina and in the vicinity of the Bahamas. The pelagic leptocephalus larvae (10–80 mm Total Length [TL]) are transported north in the Gulf Stream and across the continental shelf to arrive at estuarine inlets at ages of 53 – 110 days. Their estuarine immigration and abundance varies along the east coast, with higher levels occurring at inlets in South Carolina (North Inlet), and North Carolina (Beaufort Inlet), during the winter and early spring. Much lower abundances occur in New Jersey (Little Egg Inlet) in winter and spring and again in the summer. These ingressing individuals were euryodontic leptocephali and metamorphic stages and were shrinking to lengths of 76–52 mm TL as these stages progressed. Metamorphic individuals and glass eels subsequently settle and burrow in estuarine sediments, as do all subsequent stages, and thereby become relatively unavailable to many sampling gears. In estuaries they attained sizes up to 440 mm TL. Later, they presumably enter the ocean to spawn because that is where the smallest larvae are found.

The reproductive biology and spawning strategy of the iconic catadromous percichthyid, estuary perch Macquaria colonorum was examined from three coastal rivers of south-eastern (SE) Australia. Ovarian and testicular development followed a pattern similar to that of other percichthyids, world-wide. Females were collected in significantly larger sizes and greater numbers from all, and two of the three rivers, respectively. Mean size and age at maturity was greater for females (25.05 cm FL ± 0.85 and 3.75 yrs ± 0.08, respectively) than males (22.21 cm FL ± 0.50 and 3.28 yrs ± 0.08 respectively), with no significant difference between rivers. Trends in gonadosomatic indices indicated that M. colonorum spawn in the austral winter-spring in SE Australia. However, peak spawning occurred earlier (June-August) in the two most northern rivers (Hawkesbury and Clyde) compared with the Bemm River (September-November) further south. Ripe females were captured only in the lower reaches of estuaries throughout the spawning period in all three rivers. Mature M. colonorum females displayed a group synchronous pattern of oocyte development suggesting a multiple spawning strategy. Mean batch fecundity (F B ) was 266 583 ± 17 821 oocytes per female and relative fecundity was 377 ± 10 oocytes.g-1 body weight. There were significant power relationships between F B and fork length (FL), weight and age. Similar to other percichthyids, M. colonorum are long-lived, highly fecund and exhibit a flexible spawning strategy which is attuned to the highly variable environments in which they are found.

In most labrid fishes, large males with bright terminal phase (TP) coloration normally defend mating territories and pair spawn after following (i.e., courting) solitary females. It has also been reported that the TP males may abandon their territories and participate in group spawning when mating groups of small non-territorial males with drab initial phase (IP) coloration frequently intrude into the territories of TP males. In the similar situation of the present study, however, the territorial TP males of the threespot wrasse, Halichoeres trimaculatus, did not always participate in group spawning but continued pair spawning. Only the TP males that had few opportunities to encounter solitary IP individuals participated in group spawning, frequently following the mating groups of IP individuals. It is therefore suggested that group spawning of the territorial TP males is regarded as a tactic of making the best of the bad situation by the TP males with few opportunities to pair spawn in an area where group spawning dominates.

The sperm allocation pattern of a copulating marine cottid fish, Alcichthys alcicornis, was investigated. A total of 86 mating events using six males were conducted in aquarium tanks over 10 days, and in 36 of them, spermatozoa were collected using a false copulation method. Males released 3–8 × 108 spermatozoa in early events, with the number decreasing gradually during subsequent mating events. This sperm allocation was represented as an “early investment and tapering” pattern. It was discussed why males have significantly higher sperm release in early spawning events. The reproductive behavior consists of spawning and subsequent copulation. Spermatozoa have the ability to fertilize eggs from multiple clutches, and in earlier produced clutches the level of sperm competition should be relatively low. In addition, if early spawn happens to be the first spawn with a female, spermatozoa that are released into the water column after spawning are responsible for fertilizing the female’s first clutch. The probability of this occurring should decrease dramatically as the season progresses, due to the highly synchronous seasonal spawning of females. All of these factors should select for high sperm numbers in early ejaculates. Based on such reproductive ecology of A. alcicornis we hypothesize that this sperm allocation pattern is an adaptive reproductive strategy in response to egg availability and sperm competition occurring within the ovarian cavity.

Life history parameters associated with reproductive biology, age, and growth of the convict cichlid (also known as the zebra cichlid) Amatitlania nigrofasciata, which was introduced into the Haebaru Reservoir on Okinawa-jima Island, were estimated using 437 specimens that ranged from 13.7 to 82.9 mm standard length (SL). Lengths of females at first maturity (SL) and 50% maturity (L 50) were estimated to be 32.2 and 37.3 mm SL, respectively. The spawning period continued throughout the year, with a peak spawning cycle from March to May 2006–2007. Observations of postovulatory follicles and tertiary yolk stage oocytes indicate that convict cichlids spawn multiple times within a year. Female cichlids that hatched during the peak spawning seasons matured after October of the same year. Batch fecundity of females (32.2–61.2 mm SL) ranged from 65 to 345 (mean ± SD = 155 ± 63). Opaque zones along the outer margins of otoliths formed annually. The maximum age of male and female cichlids was 3 years. The von Bertalanffy growth formulae (VBGF) were expressed as $$ {{\hbox{L}}_{\rm{t}}}{ = 57}{.4}\left( {1 - {e^{ - 0.78\left( {t + 0.91} \right)}}} \right) $$ for females and $$ {{\hbox{L}}_{\rm{t}}}{ = 69}{.5}\left( {1 - {e^{ - 1.07\left( {t + 0.24} \right)}}} \right) $$ for males. Males grew larger than females beginning from the first year. Certain life history characteristics, such as year-round spawning and early maturation, probably contributed to the successful establishment of the convict cichlid, and this species in particular is thought to adapt and become established quickly upon introduction to freshwater systems on Okinawa-jima Island.

We used metadata on nine reproductive traits of 67 species of Brazilian iteroparous, oviparous, teleost freshwater fishes to test phenotypes associations to discriminate species that only spawn in large rivers (lotic fishes) from those capable to spawn in lentic habitats (lentic fishes). We tested the hypothesis that lotic fishes present spawning migration, shorter spawning season, single spawning, no parental care, free eggs, higher relative fecundity, faster embryogenesis, and larger size, while lentic fishes present no spawning migration, longer spawning season, multiple spawning, parental care, adhesive eggs, lower relative fecundity, slower embryogenesis, and smaller size. Our analyses supported the hypothesis but not all phenotypic associations satisfied it, specifically with regard to lentic fishes or to pairs of phenotypes typical of lentic fishes. We also concluded that spawning in large rivers is a better predictor of bionomic characters than spawning in lentic habitats, and lotic fishes are specialists compared to lentic fishes.

The ovaries of the studied 16 viviparous blenny species of the fish family Clinidae (Teleostei, Perciformes) from Australia and South Africa, are of the cystovarian type and bilobed, ending in a common short oviduct at the gonopore; they are elongated in juvenile fish, becoming bottle-shaped or oval with maturation and onset of embryogenesis, when they comprise 18–20% of the total body weight. The ovarian lumen is covered by the germinal epithelium, resting on a basal membrane. The primordial germ cells are situated along the inner side of each lobe, juxtaposed internally to the lumenal epithelium. Single primary oocytes or nests of such, each in a follicular envelope and covered externally by the lumenal epithelium forming clusters protruding into the lumen, along which the inoculated sperm settle. Two different types of reproductive strategies are demonstrated by the Australian species of Heteroclinus and Cristiceps and the South African species of Clinus and related forms. The Australian species produce high numbers of small (350 ± 50 µm in diameter) eggs that develop synchronously, while the South African species produce much fewer and larger (1.0 ± 0.1 mm) eggs, asynchronous in development. An exception in the latter group is Blennophis striatus, with eggs of ca.1.4 mm that develop synchronously. The Australian species are thus mass releasers that bear and release up to 1000 small (11 ± 1.5 mm in length) embryos/spawn, while the South African Clinus species are discrete releasers that bear eggs of various sizes and small numbers of mature for release embryos that reach up to 22 mm in length, and are released throughout the year. The cytogenesis of the oocytes and surrounding envelopes is discussed.

In many fishes, individuals prefer to associate with phenotypically similar or conspecific individuals (conspecific cueing). Such phenotypic segregation can be an important evolutionary driver, for example, in intralacustric sympatric speciation processes. I examined conspecific cueing in two species of sympatric pupfish from Laguna Chichancanab in southern Mexico: the little shoaling and highly territorial Cyprinodon beltrani and the highly shoaling but non-territorial C. simus. Females were tested for shoal species preferences in two testing scenarios: (1) a sequential choice test where shoals of four conspecific or four heterospecific (Cyprinodon sp. or Poecilia reticulata) females were presented in succession, and (2) a simultaneous choice test where female shoals of both Cyprindon species were presented concurrently. Overall, higher shoaling in C. simus was corroborated in this study. In the sequential test, no effect of the type of stimulus shoal (con- or heterospecific) on shoaling behavior was detected. In the simultaneous tests, C. beltrani, but not C. simus females showed a preference for the conspecific shoal. It seems possible that C. simus females did not evolve species recognition mechanisms because no other Cyprinodon species in the Laguna Chichancanab shows equally high shoaling, which automatically leads to the formation of single-species (i.e., C. simus-) shoals. C. simus males do not establish long-term territories, but rather spawn within shoals, whereas C. beltrani females approach males in their breeding territories to spawn. I discuss that this behavioral difference still provides a powerful reproductive isolation mechanism even in the absence of conspecific cueing in C. simus.

Results from previous research suggested that geomorphic characteristics may be important controlling factors among other microhabitat variables for spawning fish. We investigated the bedform morphology of seven spawning areas (five historic and two present spawning areas) of Chinese sturgeon (Acipenser sinensis) by analysis of relief maps of the riverbed and by field surveys. We conclude that the topographic characteristics of the spawning areas include rocky or gravelly substrate river bend, large variations in water depth and river width and a slope with moderate length and slope. The turning structure and the adverse slope may be the most important topographic characteristics for the spawning areas. Combined with the reproductive occurrence of the fish in these spawning areas, we tentatively propose a bedform morphology hypothesis for the spawning areas. We consider that a spawning area of A. sinensis should consist of three functional areas: Mating area (M), Dispersal area (D) and Incubation area (I). M, D and I are distributed along the water current and their bedform characteristics are clearly different. M is the place for mature fish to mate and spawn. It is usually below a riffle with rolling terrain. D is the place for fertilizing and dispersing fertilized eggs. It is usually in a river bend with sharp variations in terrain, such as deep pools or steep slopes. I is the place for dispersal of fertilized eggs. It is usually in long point bars or broad shallow areas with rocky substrate. This hypothesis could serve as a guideline for improving the present spawning areas or constructing new spawning areas, so as to rehabilitate the wild stock of the sturgeon.

A video camera inside an underwater housing was used to record the spawning activities of lake trout, Salvelinus namaycush, in Kushog Lake, Ontario (Canada). Contrary to the commonly accepted belief describing lake trout as the only salmonine to spawn exclusively at night, the recordings were taken during the day. Lake trout spawning behaviour is described in detail and compared with other salmonine species. The loss of female “nest-building” and assumption of a novel itinerant strategy during which females travel across the breeding grounds accompanied by a group of males, is considered to be an important change in the evolution of the lake trout’s unique mode of spawning.

The present study compares gonad structure and oogenesis in 30 species of cardinal fish (Apogonidae) from the Indo-Pacific region. In all of the species studied the ovaries are bilobed, with each lobe possessing ovigerous lamellae whose numbers and dimensions increase concomitantly with growth of the fish and reproductive stage, and correlate with the total dimensions of the particular species. In species of the genus Siphamia, the ovarian lobes are associated with a fat body that is not found in species of the other genera studied. Some of the species studied (Siphamia spp.; Archamia spp.) demonstrate group-synchronized maturation of eggs, possibly with only one spawn per reproduction season. However, most of the Apogon spp., and other genera, have unsynchronized cycles, a characteristic of multiple spawners. The various stages of previtellogenic and vitellogenic development are similar in the different species, but differ in timing and dimensions of the oocytes around which the morphogenesis of the egg envelope (chorion) and follicle begins. Differentiation of the egg envelope and follicle cells parallels the vitellogenic stages of egg development. The number of eggs was found to correlate positively with the length of the body and ovary of the fish, whereas egg diameter was found to correlate negatively with body length. The surface of the egg envelope bears ridges that form patterns of various types, whose structures and dimensions seem to be species-specific, and which in most species converge upon the single micropyle on the animal pole. The exposed ridge mazes include a special fibrous web that anchors in the micropyle. The production and importance of these ridges, as well as the correlations between egg numbers per spawn, egg dimensions, and the oral dimensions of the paternal male, are discussed.

The spotted flagtail, Kuhlia marginata (Kuhliidae) is commonly found in streams throughout the Ryukyu Archipelago, including Okinawa Island, Japan. Although it has been suggested that they spawn at sea, little is known about their migratory history. The aim of the study was to clarify their migration history based on otolith microchemistry analysis, size composition and the gonadal development of fish collected from the Genka River on Okinawa Island. All strontium/calcium (Sr/Ca) ratios of otoliths remained high around their cores, and then dropped rapidly at some distance from the core. The estimated standard length corresponding to decreases correlated with the size of new recruits collected in the river (ca. 20 mm in standard length: SL). Multiple increases, the sign for migrations into the high saline area, were recognized intermittently around the otolith margin. As the estimated SL at these increases in the Sr/Ca ratio occurred above the minimum maturation size (female: 95.5 mm SL; male: 83.5 mm SL), such multiple increases in Sr/Ca ratios were caused by spawning migration. Therefore, we conclude that the catadromous pattern of K. marginata is as follows; this species grows in the sea during the early life stage until ca. 20 mm SL and then grow in the freshwater area until maturation, before they migrate again to the sea for spawning. Sr/Ca ratio profiles also suggested that a large number of males did not return to the freshwater area after spawning, whereas females might spawn several times during their lives around the inshore area.

The green sturgeon, Acipenser medirostris, is one of two acipenserid fishes native to the temperate waters of the Pacific coast of North America. Originally, three species of sturgeon were described from this region, and this one named ‘‘medirostris’’ or ‘‘middle snout’’ based on the length of its rostrum relative to the other purported species (Ayers 1854), both of which were later determined to be white sturgeon, Acipenser transmontanus (Moyle 2002). The green sturgeon is similar in appearance to the congeneric white sturgeon, with which it cooccurs, except that its barbels are usually closer to the mouth than to the tip of the snout. Green sturgeon are heavily armored, possessing one dorsal, two lateral and two bottom rows of scutes or bony plates (Moyle 2002). In addition, there are often one or two large scutes behind the dorsal fin, as well as one behind the anal fin, which are both lacking in the white sturgeon. The common name of the species is apt due its distinctly olive-green body color, with olivaceous stripes usually present on its sides and ventral surface. Green sturgeon are currently thought to be comprised of two genetically distinct breeding populations (Israel et al. 2004): a northern distinct population segment (DPS) consisting of fish that spawn in the Rogue River, Oregon (Erickson et al. 2002), and the Klamath River, California (Van Eenennaam et al. 2001), and a southern DPS that spawns in the Sacramento River, California. Increasingly, many fish species are being recognized as consisting of multiple, genetically distinct stocks. In many cases, these stocks are managed separately because of distinctive phenotypic, physiological, and behavioral characteristics representative of the unique adaptations each stock has to the environmental conditions in a particular habitat (Waples 1995). Although little is known about what distinguishes these green sturgeon populations biologically, several unique physical characteristics differentiate the river systems in which they occur. Tidal flows in an expansive estuary, voluminous flows, long river length, and multiple tributaries in an extensive watershed distinguish the Sacramento River from the Rogue and Klamath Rivers with their small estuaries, relatively short length, and smaller watersheds. Based on the best information available to the National Marine Fisheries Service (Adams et al. in press), the southern DPS was A. P. Klimley (&) P. J. Allen J. T. Kelly Department of Wildlife, Fish & Conservation Biology, University of California, One Shields Avenue, Davis, CA 95616, USA e-mail: apklimley@ucdavis.edu

Interspecific interactions can determine the abundance and distributions of animals. Seaweed blennies, Parablennius marmoreus, and tesselated blennies, Hypsoblennius invemar, are found in barnacle cavities on offshore petroleum platforms in the northern Gulf of Mexico. I measured the interspecific resource defense interactions between these fishes in aquaria. Seaweed blennies were dominant over tesselated blennies when equal-sized fishes were tested. No difference in dominance was found when tesselated blennies had a 10% advantage in size. However, tesselated blennies were able to successfully defend cavities against equal-sized competitors when given the advantage of prior residence. This prior residence advantage persisted despite seaweed blennies having the advantage of past experience. Seaweed blennies attain a larger size on petroleum platforms, but empty barnacle cavities are common in this environment. Tesselated blennies are able to colonize and successfully spawn because they can enter an empty barnacle cavity, gain the advantage of prior residence, and successfully defend this cavity.

Surubim, Pseudoplatystoma corruscans, is the most valuable commercial and recreational fish in the Sao Francisco River, but little is known about adult migration and spawning. Movements of 24 females (9.5–29.0 kg), which were radio-tagged just downstream of Tres Marias Dam (TMD) at river kilometer 2,109 and at Pirapora Rapids (PR) 129 km downstream of TMD, suggest the following conceptual model of adult female migration and spawning. The tagged surubims used only 274 km of the main stem downstream of TMD and two tributaries, the Velhas and Abaete rivers. Migration style was dualistic with non-migratory (resident) and migratory fish. Pre-spawning females swam at ground speeds of up to 31 km day-1 in late September–December to pre-spawning staging sites located 0–11 km from the spawning ground. In the spawning season (November–March), pre-spawning females migrated back and forth from nearby pre-spawning staging sites to PR for short visits to spawn, mostly during floods. Multiple visits to the spawning site suggest surubim is a multiple spawner. Most post-spawning surubims left the spawning ground to forage elsewhere, but some stayed at the spawning site until the next spawning season. Post-spawning migrants swam up or downstream at ground speeds up to 29 km day-1 during January–March. Construction of proposed dams in the main stem and tributaries downstream of TMD will greatly reduce surubim abundance by blocking migrations and changing the river into reservoirs that eliminate riverine spawning and non-spawning habitats, and possibly, cause extirpation of populations.

Three Acipenseridae species live in the rivers and marine waters of the Khabarovsk Territory, Russia: Sakhalin sturgeon, Acipenser mikadoi, Amur sturgeon, A. schrenckii, and kaluga, Huso dauricus. We review the general biology and life history of each species, including their historic and current distributions, and examine current paleogeographic theories to outline the possible origin and evolution of these three species in the Amur River, Sea of Okhotsk, and Sea of Japan biogeographic province. Apparently, these species have evolved during distinct geologic time periods, which has reinforced the reproductive isolation of these species although hybridization does occur. They have convergently adapted to the unique environmental conditions of the Amur River and Russian Maritime regions, and yet developed behavioral adaptations to reduce competition between species. Sakhalin sturgeon is the least studied species among anadromous sturgeon in the world. This species is highly migratory and spends the majority of its life in the ocean only returning to natal rivers to spawn. Amur sturgeon and kaluga are distributed throughout the Amur River basin and the estuary and share many life history traits. They are both represented by distinct morphs. Additionally, we present size and weight relationships to estimate the growth of Amur sturgeon and kaluga. All three species have suffered declines in abundance due to over fishing and their contemporary distributions have contracted compared to their historic ranges. We identify gaps in knowledge and suggest further research useful for guiding management of each species.