Search

While the olfactory cue hypothesis has been proposed for spawning migration of silver eels, it has been shown that olfactory cells and associated mucus cells degenerate in male and female eels after hormonally induced sexual maturation. However, the degeneration of the olfactory organ could be a real event in the sequence of maturation, or may be an unnatural side effect of the hormone treatment itself. We morphologically and histologically examined the olfactory rosettes of hormone-untreated and hormone-treated (mixture of hCG and PG) giant mottled eel (Anguilla marmorata) and Japanese eel (A. japonica). The olfactory rosette from all the hormone-treated specimens significantly degenerated at various degeneration levels even in sexually immature specimens, indicating the side effect of the hormone-treatment. However, a sexually immature non-hormone treated female A. marmorata (87.4 cm TL, 199.4 g BW, at less advanced maturity) had slightly degenerated olfactory rosette. Further studies should focus on conducting natural degeneration of the olfactory rosette during the sexual maturation in tropical eels.

This study investigated whether irradiation of a specific light wavelength could affect the sex differentiation of fish. We first found that the photoreceptor genes responsible for receiving red, green, and ultraviolet light were expressed in the eyes of medaka during the sex differentiation period. Second, we revealed that testes developed in 15.9% of genotypic females reared under green light irradiation. These female-to-male sex-reversed fish (i.e. neo-males) showed male-specific secondary sexual characteristics and produced motile sperm. Finally, progeny tests using the sperm of neo-males (XX) and eggs of normal females (XX) revealed that all F1 offspring were female, indicating for the first time in animals that irradiation with light of a specific wavelength can trigger sex reversal.

Efficient production of beneficial metabolites by microalgae using light-emitting diodes (LED) is attracting more interest. In batch cultures, metabolic changes that occur with nutrient deficiency over time must be monitored to estimate the metabolite content. Our previous study showed that nutrient deficiency in Nannochloropsis oculata can be briefly evaluated by measuring the absorption ratio at 490 and 680 nm (Abs490/Abs680). However, little is known about the relation with this ratio and metabolic change, particularly in LED light-conditioned cultures. In this study, we investigate if Abs490/Abs680 can be an indicator of the biochemical status of N. oculata cultured under various LED color regimes. Three LED treatments were used: Blue (B), Blue + Red (BR), and Red (R). In all LED treatments, the Abs490/Abs680 decreased for several days and then increased when phosphate was limited or non-existent. The trends in the C16:0 and C20:5ɷ3 proportions and chlorophyll a content commonly changed at the turning points of the Abs490/Abs680. Furthermore, significant correlations were found among the metabolic state and absorption ratio, except in treatment R. We suggest that spectrophotometry can be used for monitoring metabolic changes in N. oculata cultures under various LED irradiance, unless there is excessive 630 nm-red light exposure.

Knowledge on the visual spectral sensitivity of a given fish is important for determi‐ nation of optimal light conditions for improvement of fish rearing in aquaculture. Sutchi catfish (Pangasianodon hypophthalmus Sauvage 1878) is an important freshwa‐ ter fish species in Southeast Asia. The present study aimed to understand the visual spectral sensitivity of juvenile sutchi catfish through spectrophotometric measure‐ ment of the spectral absorbance of wholemounts of retinae. The spectral absorbance curves obtained from the spectrophotometric measurement indicated a parabolic shape. The curves for retinae photo‐bleached with initial flash of blue, green and yel‐ low lights, respectively had a peak at approximately 560 nm, which were the same as the curve for retinae photo‐bleached with broad wavelength light. On the other hand, the curve for retinae photo‐bleached with initial flash of red light had a peak shifted prominently toward shorter light wavelength at approximately 540 nm. This prominent shift of peak implied that the retinae of juvenile sutchi catfish absorb light wavelength of red. Therefore, the present results clearly suggested that juvenile sutchi catfish utilises longer light wavelengths.

With New Washington-Batan estuary as study site, this study determined the impact of Typhoon Haiyan on capture fisheries through data that were collected before and after the typhoon event. To validate these results and to determine other related information (e.g., recovery of fishing after typhoon), key interviews and focus group discussions were conducted. The immediate impact of the typhoon event was disruption of fishing livelihood due to damage of fishing gears as about 94% of stationary fishing gears had considerable damage. Resumption of fishing operations varied largely among fishers depending on the degree of gear damage. Reconstruction of damaged stationary gears was hampered mainly by the financial capacity of fishers and the acute supply of bamboo which is the main component in the construction of these fishing gears. We also discuss typhoon impacts on other fishing gears such as line fishing, gillnets, and pots. These information are valuable in understanding impacts of extreme weather events on tropical small-scale fisheries so that managers may be able to devise measures to reduce vulnerabilities among coastal resource users.

We propose a new analytical method for determining the response threshold in electroretinogram (ERG) in which the wave shows a biphasic slow dc-potential shift. This method uses the recorded wave to the highest intensity stimuli in each wavelength tested as a template wave f(t), and it was compared with other recorded waves obtained under lower intensities g(t). Our test recordings in medaka Oryzias latipes were analogous between the template and the compared waveforms, although there were differences in amplitude and time lag (τ, peak time difference) which occurred as a result of the difference in stimulus intensity. Cross-correlation analysis was applied. Based on the obtained cross-correlation function Cfg(τ) in each comparison, τ was determined as the time lag at which the cross-correlation coefficient Rfg(τ) showed the maximum value. Determined thresholds that were based on both the experimenter's visual inspection and this new method agreed well when the adoption condition was set to satisfy R(τ) ≥ 0.7 and τ ≤ 150 ms in scotopic or τ ≤ 120 ms in photopic conditions. We concluded that this “template wave matching method” is a quick and reliable objective assessment that can be used to determine the threshold. This study analyzed ERG recordings in response to 6 kinds of wavelength light stimuli (380 nm to 620 nm) at different photon flux densities. We report the threshold levels and relative spectral sensitivities in scotopic and photopic vision of medaka.

Size-selective fishing operation types and skippers’ fishing strategies in operation type combinations were analyzed using fishing data from Thai tuna purse seiners in the Western Indian Ocean during 2005–2007. Catch species and size compositions of tropical tuna, i.e., skipjack, yellowfin and bigeye tunas, were compared among operation types, including free school (FS), fish aggregating device, natural log, and other floating objects operations. FS operation was found to be the most size-selective technique, and caught the fewest small-sized individuals, while the associated operations were less size-selective. Fishing strategy analysis showed that success rates and differences between optimistic and actual values represent economic risk. FS operation holds the highest risk; however, it represents potentially high-revenue fishing because of its ability to catch large-sized individuals and high-priced species. Skipper skills are believed to affect a skipper’s fishing strategy, and specialist and generalist skippers were both identified in this analysis. The specialists achieved high revenue by overcoming the risks of FS operation via their skills, while generalists distributed fishing efforts over operation types to avoid risks. Simulation results suggested that high- and moderate- skilled skippers can shift to FS operations with no revenue decline to respond to the policies of the Tuna Regional Fishery Management Organizations, which increasingly promote FS operation.

Authors would like to thank Southeast Asian Fisheries Development Center (SEAFDEC) for providing the fishing data. Kyushu Chuou Uoichi Co., Ltd., Kagoshima, Japan, is appreciated for supporting our fish measurement. This study is supported by a scholarship from the Agricultural Research Development Agency (ARDA), Thailand. Our sincere appreciation is extended to Dr. Shiela Villamor who kindly checked the English of this manuscript.

Hao-Yi Chang, Tzu-Hao Lin, Kazuhiko Anraku, and Yi Ta Shao (2018) Short-term exposure to strong underwater noise is known to seriously impact fish. However, the chronic physiological effects of continuous exposure to weak noise, i.e. the operation noise from offshore wind farms (OWF), remain unclear. Since more and more OWF will be built in the near future, their operation noise is an emerging ecological issue. To investigate the long-term physiological effects of such underwater noise on fish, black porgies (Acanthopagrus schlegelii) were exposed to two types of simulated wind farm noise—quiet (QC: 109 dB re 1 μPa / 125.4 Hz; approx. 100 m away from the wind turbine) and noisy (NC: 138 dB re 1 μPa / 125.4 Hz; near the turbine)—for up to 2 weeks. Measurement of auditory-evoked potentials showed that black porgies can hear sound stimuli under both NC and QC scenarios. Although no significant difference was found in plasma cortisol levels, the fish under NC conditions exhibited higher plasma reactive oxygen species (ROS) levels than the control group at week 2. Moreover, alterations were found in mRNA levels of hepatic antioxidant-related genes (sod1, cat and gpx), with cat downregulated and gpx upregulated after one week of QC exposure. Our results suggest that the black porgy may adapt to QC levels of noise by modulating the antioxidant system to keep ROS levels low. However, such antioxidant response was not observed under NC conditions; instead, ROS accumulated to measurably higher levels. This study suggests that continuous OWF operation noise represents a potential stressor to fish. Furthermore, this is the first study to demonstrate that chronic exposure to noise could induce ROS accumulation in fish plasma.

We hypothesized that fish with red-sensitive retina would be stressed by red light and thus inhibited in somatic growth. Red sea bream (Pagrus major) juveniles (total length =3 cm) with red-sensitive retina were chosen to test this hypothesis. We examined the effect of different color lights (red with λmax 605 nm; green with λmax 540 nm; blue with λmax at 435 nm; and white with full spectrum) on unfed juveniles in laboratory tanks. Stress level was measured by the plasma cortisol and glucose concentrations, and nutritional status by muscle RNA/DNA ratio. Under red light, plasma cortisol and glucose, and muscle RNA/DNA were significantly higher than under green, blue, or white light. Our hypothesis was partly supported by previous findings on the effects of the color environment and spectral sensitivity of reared fishes. However, the levels of cortisol, glucose, and RNA/DNA in this study were low compared to published values. It seems that hatchery-bred juvenile red sea bream have adapted to red-rich surface light and are able to cope with the stress of living in surface floating cages which is so different from their deep-water habitats.

To understand how early juvenile yellowfin tuna use the habitat and environment provided by fish aggregating devices (FADs), fish (19–31 cm FL) implanted with ultrasonic transmitters into their abdominal cavities were released in a network of payaos in Panay Gulf, the Philippines. Self-recording receivers were attached to the anchor ropes of the payaos to detect the presence of the fish. Some aspects of the behavior of juveniles were similar to those reported in adults. One juvenile showed a diurnal vertical swimming pattern, swam within a limited shallow range during the nighttime, and dived to deeper waters during the daytime. Two juveniles performed deep dives over 100 m during payao-to-payao excursion. Three juveniles showed a diurnal horizontal swimming pattern that was synchronized. In contrast, juveniles stayed

Larvae and juveniles of barramundi Lates calcarifer (Bloch) were examined for the development of the retina, occurrence of the retinomotor response and retinal tapetum and change in eye size with age in days. The barramundi hatched with unpigmented non-functional eyes in which retinal cells had not yet differentiated into the various elements. Soon it was followed by rapid changes in the histology of the retina. Two-day-old larvae had a well-pigmented retina with area temporalis which would allow acute vision and prey attack in the nasal direction. At 10 days, rod cells and the retinal tapetum first appeared in the retina and the retinomotor response first occurred; these would allow feeding in dim light. The retinal tapetum moved in unison with the cones and the pigment epithelium during the retinomotor response. At 26 days, the horizontal cells were divided into two layers and the twin cones appeared. These changes in the eyes occurred concurrently or in anticipation of behavioural changes, such as the ...

SUMMARYAntennules have been reported to influence localization of distant food odors, sex discrimination, and agonistic and social behaviors of decapod crustaceans. Although olfaction by the antennules is largely recognized, information on the sensitivity of antennules to hydrodynamic stimuli has been scant. In red swamp crayfish Procambarus clarkii antennules, mechanosensory setae outnumber the chemosensory setae. We studied the mechanosensitivity of crayfish antennules by recording neural activities from isolated antennules in response to sinusoidal dipole stimuli. Both the lateral and the medial flagellum of the antennules responded to hydrodynamic stimuli, although the medial flagellum showed more sensitivity at frequencies higher than 60 Hz. The most dominant setae present on the stimulated site were the simple setal type. Although both lateral and medial flagella are capable of detecting chemical and hydrodynamic cues, results from neural responses, morphological observations and antennular behavior observations indicate that the lateral flagellum of P. clarkii functions as an olfactory organ whereas the medial flagellum complements as a hydrodynamic receptor. It appears that in crayfish antennular sensory processing, crayfish simultaneously use chemical and hydrodynamic information. We have compared our data with the threshold of fish lateral line to the same stimuli and we discuss probable similarities in response properties.

To understand how early juvenile yellowfin tuna use the habitat and environment provided by fish aggregating devices (FADs), fish (19–31 cm FL) implanted with ultrasonic transmitters into their abdominal cavities were released in a network of payaos in Panay Gulf, the Philippines. Self-recording receivers were attached to the anchor ropes of the payaos to detect the presence of the fish. Some aspects of the behavior of juveniles were similar to those reported in adults. One juvenile showed a diurnal vertical swimming pattern, swam within a limited shallow range during the nighttime, and dived to deeper waters during the daytime. Two juveniles performed deep dives over 100 m during payao-to-payao excursion. Three juveniles showed a diurnal horizontal swimming pattern that was synchronized. In contrast, juveniles stayed

The food intake and prey composition of payao-associated Brama orcini were compared with individuals captured in open waters from February to May 2005 in Panay Gulf. An experimental multi-hooked handline was used to catch fish at the two sites. The food items of payao-associated and free-swimming fish in this fishing ground overlap; however, the total frequency of occurrence and abundance of all prey items were both higher in free-swimming fish than in payao-associated individuals. Invertebrates seemed to be preferred by this fish, and the ratio of prey weight to its body weight was significantly higher in unassociated fish than in fish caught near payaos. In open waters, B. orcini feeds predominantly on the sergestid shrimp Acetes sp., but it alters its diet by feeding on the small finfish that also aggregates near the payaos when the fish is associated with the floating structures. These results should be verified since they may be useful in managing the fishery resources aggregating near payao.

Hatchling sea turtles (Caretta caretta) emerge from their beach nests at night and crawl seaward immediately, even where the sea is not visible to them. This sea-finding ability of hatchlings is one of the outstanding phenomena of animal orientation. The primary sea-finding mechanism is an orientation towards light, and blindfolded hatchlings could not find the sea. Hatchlings of loggerhead turtles avoid yellow and orange light and are strongly attracted to light in the near-ultraviolet to green part of the spectrum. Here we demonstrate in experiments at a nesting beach that (1) loggerhead hatchlings orient to near-ultraviolet radiation, and (2) the intensity of near-ultraviolet radiation is always higher seaward than landward on all nights. These results are consistent with long-term monitoring data that show emergence of loggerhead hatchlings takes place during any phase and position of the moon. To prevent mis-orientation of hatchlings, roads, and human settlements fronting turtle nesting beaches shoul...

Sound generated by a payao, an anchored bamboo fish aggregating device, is believed to be attractive to fish; but until now, there is no available record of payao-generated sound. This study presents payao-generated sound recorded by a hydrophone at water depths of 5, 10 and 15 m from a fixed distance of 3 m relative to the payao, and compares the sound with the auditory sensitivity of jack mackerel Trachurus japonicus measured at discrete frequencies from 100 to 2000 Hz using the auditory brainstem response protocol. A consistent peak appeared in the sound spectrum at 49 Hz and showed an increasing sound pressure level with depth, which suggests that payao sound may come from the anchor rope. However, the contribution of the bamboo raft can not yet be discounted. The hearing threshold curve indicated that the most sensitive frequency range in jack mackerel is from 92.1 dB at 800 Hz to 111.0 dB at 200 Hz. These results show that the dominant frequency range of payao sound does not correspond with the high sensitivity frequency range of fish hearing.

Background Vision, an important sensory modality of many animals, exhibits plasticity in that it adapts to environmental conditions to maintain its sensory efficiency. Nuptial coloration is used to attract mates and hence should be tightly coupled to vision. In Taiwan, two closely related bitterlings (Paratanakia himantegus himantegus and Paratanakia himantegus chii) with different male nuptial colorations reside in different habitats. We compared the visual spectral sensitivities of these subspecies with the ambient light spectra of their habitats to determine whether their visual abilities correspond with photic parameters and correlate with nuptial colorations. Results The electroretinogram (ERG) results revealed that the relative spectral sensitivity of P. h. himantegus was higher at 670 nm, but lower at 370 nm, than the sensitivity of P. h. chii. Both bitterlings could perceive and reflect UV light, but the UV reflection patterns differed between genders. Furthermore, the relative irradiance intensity of the light spectra in the habitat of P. h. himantegus was higher at long wavelengths (480–700 nm), but lower at short wavelengths (350–450 nm), than the light spectra in the habitats of P. h. chii. Conclusions Two phylogenetically closely related bitterlings, P. h. himantegus and P. h. chii, dwell in different waters and exhibit different nuptial colorations and spectral sensitivities, which may be the results of speciation by sensory drive. Sensory ability and signal diversity accommodating photic environment may promote diversity of bitterling fishes. UV light was demonstrated to be a possible component of bitterling visual communication. The UV cue may assist bitterlings in gender identification.

ツキヒガイ外套眼の光受容特性の解明を目的として大小 2 種の外套眼を組織解剖学的に調べ，更に網膜電図（ERG）によって分光応答特性と臨界融合周波数（cff）を調べた。外套眼は細胞レンズや視細胞をもち，その構造はホタテガイのものと類似した。分光応答特性は，大小 2 種の外套眼ともに 470～520 nm の波長にピークがみられた。cff は 1.3 Hz～1.5 Hz の間にあり，魚類の cff と比較して極めて低かった。この cff から，ツキヒガイ外套眼はゆっくり動く物体や陰影の認識に関係すると推察された。

An underwater camera was used to record the behavior of the crab, Charybdis japonica, towards two baited pots. These were commercial collapsible pots commonly used by Japanese fishermen to catch crabs. One was box shaped with two slit entrances at the ends, while the other was dome shaped and had two open funnel entrances. The pots were placed on the bottom of a pond that was connected to Kagoshima Bay, southern Japan. Underwater video recordings were used to study the different behaviors of the crabs towards the two types of pot. Crabs approached the pot mostly by crawling up current (75%) following the bait odor trail. They made several attempts to enter the pot until they reached the entrance or otherwise they gave up. While the dome-shaped pot allowed the crabs to enter it easily by crawling sideways, the box-shaped pot's tight slit entrances and netting material prevented the crabs from getting in due to entanglement of their spines on the netting. Ingress could only be achieved after several trials and mostly by crawling backwards into the pots. The dome-shaped pot was more efficient (100%) than the box- shaped pot (31%) in catching crabs that came in contact with it.

The effects of exposing the taste receptors to two common aquaculture therapeutants, potassium permanganate (KMnO4) and formalin, on the gustatory responses in the Nile tilapia Oreochromis niloticus (Linnaeus) were studied using an electrophysiological approach. Electrical responses to the stimuli before and after perfusing the receptors with the toxicants were compared. Responses to 1.0 mM l-methionine (l-met) were significantly reduced when the receptors were perfused with 2.0 mg L−1 KMnO4 or 200.0 mg L−1 formalin. KMnO4 suppressed the responses to 56%, whereas formalin reduced them to 83%. Both toxicants reduced the responses to l-arginine to a similar extent to that of l-met, indicating that the action of the toxicants is not specific for the receptor sites for amino acids. On the other hand, the toxicants suppressed the responses to quinine significantly more than those to amino acids, which indicates that the transduction pathways for bitter substances are much more sensitive. The suppressions were reversible, suggesting that these toxicants do not cause any permanent damage to the physiological features of the taste receptors, but only interfere with their normal functioning. The possible mechanisms of suppression and their consequences on the feeding process are discussed.

The gustatory sensitivity of the Nile tilapia, Oreochromis niloticus L., to different amino acids was studied using an electrophysiological approach. The electrical responses were recorded from a branch of the facial nerve innervating the external taste buds of the upper lip. The relative stimulatory effectiveness (RSE) of nine amino acids and betaine were determined at a concentration of 1 mm and all of them elicited neural responses. This species responded well to the neutral, basic and acidic amino acids. The most stimulatory amino acids were L-histidine, L-arginine, L-serine, L-methionine and L-glutamine; L-proline and betaine were the least stimulatory. The results of this study suggest that the Nile tilapia has high external gustatory sensitivity to some amino acids as a physiological adaptation to search effectively for their sources. The effect of the pH, ranging from 4.0 to 9.0, on the RSE of three neutral amino acids and artificial pond water (APW) was also studied. The RSE increased below pH 6.0 and was relatively unaffected from 7.0 to 9.0, indicating that acidified stimulants are highly stimulatory in this species. Nile tilapia did not discriminate the pH of APW as effectively as some of the species studied earlier.

感光色素を一種類しかもたないタコ類は色盲とされる。これを行動実験で検証するために, スナダコ5個体とマダコ7個体を用いて色覚を確かめる学習実験を行った。供試個体を負刺激球(白球あるいは灰色球)と同時呈示した青球(直径25mm, 反射スペクトルのλmax=460nm)に触れてから餌を摂るよう条件付けた後, 負刺激球を明度が段階的に異なる灰色球に換えて移調試験を行った。移調試験では, スナダコは灰色球の明度にかかわらず有意に高頻度で青球を選択し, 色覚をもつ可能性が示された。マダコは灰色球の明度によって選択球が変わり, 色盲であると結論された。

タコが何色の隠れ場を好んで選択するか, また選択する色は背景色の違いによって変化するかを調べることを目的とし, 供試個体にマダコおよびスナダコを用いて水槽内行動実験を行った。高照度下で黒, 赤, 橙, 黄, 緑, 青, 白の7色, 低照度下で黒, 黄, 青の3色を背景色とし, 円筒形の隠れ場8色(黒, 赤, 橙, 黄, 緑, 青, 白および透明)を設置し, 30分おきのタコの状態を目視観察, 記録した。背景色にかかわらず黒, 赤, 橙の隠れ場が両種のタコに共通して高頻度で選択された。マダコとスナダコで異なる行動結果も得られたが, スペクトル感度の違いによるものと考えられ, 両種とも, 暗さを好む傾向があると結論された。

ツキヒガイを短時間のうちに開殻させ軟体部の手術が可能な方法として塩化マグネシウム溶液を閉殻筋に注射する方法を採用し, その確立を目的とした。注射液は自然海水および0.2M, 0.4M, 0.6Mの塩化マグネシウム溶液, 注射量は1ml, 3ml, 5mlとした。いずれの条件下でも, 注射直後腹縁中央が開殻度にして9-12度開いた。0.4M溶液5ml, 0.6M溶液3ml, 0.6M溶液5mlを注射した時は, 接触刺激によっても閉殻筋の収縮は起こらず, 軟体部の手術が可能であった。この方法は, 感覚閉塞等の種々の実験技術に応用できる。

As a part of a marine ranching project, this study examined responses to tone-bursts of different frequencies by flounder juveniles which had been conditioned to come to a sound source of 300Hz tone-bursts in a fish cage. After completion of conditioning, the flounders showed the conditioned responses to 1s tone-bursts of frequencies of 200-800Hz with a peak sensitivity at 300Hz, and a slight and short response to a continuous sound of 300Hz immediately after the sound projection, coinciding with the previous finding with res sea bream juveniles. The bimodal pattern of sound frequency-pressure threshold concluded that this conditioned response was mediated by the inner ear in response to particle displacement. This pattern, however, was different from a reported audiogram with a peak seak sensitivity at 100Hz, probably because of the effect of frequency of the conditioned sound.

In attempts to enthance fish stocks and increase the harvest of grown fish after release in Japanese coastal waters, classical conditioning of fish to sound before the release has been tried with red sea bream and some other species, The common sound used in the conditioning is a 300Hz, 1s tone burst, but this does not seem to be effective in attracting conditioned fish after release. This paper describes a key component of the sound to which red sea bream were conditioned. A group of one-year old and three groups of younger juvenile red sea bream were conditioned to the 300Hz sound during feeding in separate floating cages. Upon completion of the conditioning, the fish were exposed to 1s tone bursts of frequencies 100 to 5000Hz and of various sound pressures. The juveniles showed positive responses at 100 to 3000Hz and best responses at 300Hz and at 1500Hz, they were attracted to the sound origin upon projection but left the sound origin soon after. A similar response pattern was observed at 200 to 3000Hz in the one-year old sea bream, with best responses at 300Hz. The one-year old fish showed typical avoidance response to 100Hz, 1s tone bursts, which showed that the lateral line system mediated the response but that the lateral line is still poorly developed in the juveniles. When 300Hz, 1s tone bursts were applied at various pulse intervals, the juveniles responded positively to bursts at 0.04 to 5s intervals. These results imply that the key component of the sound is the rising pressure and thus the conditioned fish would be attracted to any intermittent sound after release.

One of the most commonly cited problems regarding age determination in crustaceans is the absence of any calcified structures containing growth rings. The question addressed by this study is: do the zygocardic, prepyloric and pyloric ossicles of the gastric mill of decapod crustaceans contain any record of growth? Answering this question is a rudimentary step to broaden the current understanding of calcified structures in reference to ageing crustaceans. Five species of decapod crustaceans are selected for cross section analysis. Transverse cross sections of the gastric ossicles from all species examined revealed the presence of alternating translucent and opaque growth rings, similar in appearance to those that are routinely examined in fish otoliths. Elucidation of the gastric ossicle growth record may present the opportunity to reduce the current uncertainties in modelling non-uniform growth in crustaceans, and provide greater compatibility across currently applied methods of age determination. Keywords:ageing crustaceans; calcified structures; decapod crustaceans; gastric mill; pyloric ossicles; zygocardic ossicles

This chapter talks about the incubation of the endangered Japanese crayfish ( Cambaroides japonicus ) eggs in vitro at different water conditions - pH and water temperature in order to understand the suitable egg rearing conditions. Crayfish eggs sampled just after spawning do not survive until they hatch out. This result strongly suggests that early stage of eggs effectively develop when attached to the pleopods of the mother. In contrast, crayfish eggs before hatching were able to survive in a wide range of water conditions. However, they were weak for acid condition. These findings suggest that acid conditions caused by human activities can spur the drastic decline of Japanese crayfish. It is estimated that the eggs of C. japonicus do not hatch in acidified water, and their optimal hatching temperature is different with each local population. Keywords: Cambaroides japonicus ; Japanese crayfish eggs; optimal hatching temperature; pH; water temperature

Three juvenile yellowfin tuna (22–26 cm FL) were monitored around a payao (FAD: Fish Aggregating Device) in Panay Gulf, the Philippines. A receiver was attached to the anchor line of the payao, and ultrasonic transmitters were implanted into the abdominal cavities of the fish. Juvenile yellowfin tuna swam within a limited shallow range during nighttime and dived to deeper waters, maximum 105 m, during daytime, then moved away from the payao at midnight. One juvenile yellowfin tuna was recaptured 2 days after release by handline in the same payao, and two juvenile yellowfin tuna were recaptured 12 days after release by ringnet in another payao over 3 km away. These recaptures indicate that the fish were active enough to feed and swim, and also show the feasibility of undertaking telemetry studies on juvenile yellowfin tuna.

Optomotor studies have shown that three-spined sticklebacks (Gasterosteus aculeatus) are more sensitive to red during summer than winter, which may be related to the need to detect the red breeding colour of males. This study aimed to determine whether this change of red light sensitivity is specifically related to reproductive physiology. The mRNA levels of opsin genes were examined in the retinae of sexually mature and immature fish, as well as in sham-operated males, castrated control males, or castrated males implanted with androgen 11-ketoandrostenedione (11 KA), maintained under stimulatory (L16:D8) or inhibitory (L8:D16) photoperiods. In both sexes, red-sensitive opsin gene (lws) mRNA levels were higher in sexually mature than in immature fish. Under L16:D8, lws mRNA levels were higher in intact than in castrated males, and were up-regulated by 11 KA treatment in castrated males. Moreover, electroretinogram data confirmed that sexual maturation resulted in higher relative red spectral sensitivity. Mature males under L16:D8 were more sensitive to red light than males under L8:D16. Red light sensitivity under L16:D8 was diminished by castration, but increased by 11 KA treatment. Thus, in sexually mature male sticklebacks, androgen is a key factor in enhancing sensitivity to red light via regulation of opsin gene expression. This is the first study to demonstrate that sex hormones can regulate spectral vision sensitivity.

The substance 2-methylisoborneol (MIB) often affects aquatic organisms and causes problem of off-flavours in fish. In order to know how fish become tainted with MIB, response and chemical sensitivity of three freshwater fishes to MIB were examined behaviorally and electrophysiologically. The electrocardiographic tests showed that the threshold of detection for this compound was 4.8 × 10−5 ngl−1 for the Nile tilapia and 2.1 × 10−5 ngl−1 for the rainbow trout. Fish whose olfactory rosettes were removed also showed the cardiac response to MIB, but the threshold increased by 3 and 5 orders of magnitude in the Nile tilapia and rainbow trout respectively. The recordings of neural response of the olfactory tract of the carp to MIB solutions showed the olfactory threshold at a concentration of 4 × 10−8 ngl−1. In behavioral tests in tanks, MIB solutions did not attract these fishes and evoked no avoidance in these fishes. It was concluded that, while freshwater fishes are extremely sensitive to MIB, they would not escape from waters contaminated with MIB and thus easily be tainted with MIB.

In his Correspondence article ([p. 871][1]), DeForest Mellon, Jr argues that the type of seta in our report ([Monteclaro et al., 2010][2]) was erroneously identified. In response, we would like to make the following remarks. Stimulation of an antennule that was either seta-less or without plumose

人工種苗のマダイの鼻孔形態をふ化から63日間観察し, 鼻孔隔離皮の形成過程を明らかにした。ふ化後26日以降では観察した全個体に鼻孔隔皮形成組織が出現したがその発達過程は個体によって異なった。最終的に4割の個体が鼻孔隔皮を形成し前・後鼻孔を完成した。その他の個体では隔皮形成組織に発達が認められないため, 鼻孔異常は隔皮形成組織の発達不良によると考えられた。ふ化後40日以降では鼻孔隔皮形成個体と未形成個体の出現頻度はほぼ一定するので, この段階で将来とも正常鼻孔または異常鼻孔個体となるかを識別できると考えられた。

Hydrodynamic static pressures on the body surface of fish generated by conspecifics parallely swimming were measured in a flume tank, and they were compared with those generated by changing the position of two individuals under different flow velocities. Two dead common carp (BL=20 cm), fixed in 20% of formalin, were used. Pressure was measured by a manometer connected to the ends of three aluminum pipes (inner diameter=3 mm), which were inserted perpendicularly to the body axis from right to left in the control fish. The openings of the pipes were located on head, trunk, and caudal regions, and each was on the infraorbital or trunk canal lateral lines. The target fish was moved on the horizontal XY plane using a traverse device. Although pressures changed depending on the regions measured, changes of pressure according to position and current velocity were relatively low in the caudal region. The absolute values of the pressure increased as flow velocity increased, and decreased with an increase in the d...