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The endangered twoline skiffia Neotoca bilineata, a viviparous fish of the subfamily Goodeinae, endemic to central Mexico (inhabiting two basins, Cuitzeo and Lerma-Santiago) was evaluated using genetic and habitat information. The genetic variation of all remaining populations of the species was analysed using both mitochondrial and microsatellite markers and their habitat conditions were assessed using a water quality index ( IWQ). An 80% local extinction was found across the distribution of N. bilineata. The species was found in three of the 16 historical localities plus one previously unreported site. Most areas inhabited by the remaining populations had IWQ scores unsuitable for the conservation of freshwater biodiversity. Populations showed low but significant genetic differentiation with both markers (mtDNA φST = 0·076, P < 0·001; microsatellite FST = 0·314, P < 0·001). Borbollon, in the Cuitzeo Basin, showed the highest level of differentiation and was identified as a single genetic unit by Bayesian assignment methods. Rio Grande de Morelia and Salamanca populations showed the highest genetic diversity and also a high migration rate facilitated by an artificial channel that connected the two basins. Overall, high genetic diversity values were observed compared with other freshwater fishes (average Na = 16 alleles and loci and mean ± s.d. Ho = 0·63 ± 0·10 and nucleotide diversity π = 0·006). This suggests that the observed genetic diversity has not diminished as rapidly as the species' habitat destruction. No evidence of correlation between habitat conditions and genetic diversity was found. The current pattern of genetic diversity may be the result of both historical factors and recent modifications of the hydrological system. The main threat to the species may be the rapid habitat deterioration and associated demographic stochasticity rather than genetic factors. [ABSTRACT FROM AUTHOR]

Abstract: Interbrood period, gonad development, and total lipid content throughout the oogenesis and spermatogenesis processes of the subtropical euphausiid Nyctiphanes simplex were studied. Specimens were collected during six oceanographic cruises in Bahía Magdalena (March, July, and December 2004) and in the Gulf of California (November 2005 and January and July 2007). Females attained first spawning when ∼7.5mm total length (>52 days old). Histological evidence indicates that N. simplex females have group-synchronous ovaries, able to produce four broods per gonadic cycle, since ovigerous females develop simultaneously in three and four distinct substages (Oc1, Oc2, Oc3, and Oc4) in their gonads. Once females mature, as shown by pale pink gonads, they may reabsorb their gonads in <4 days. Direct observations indicate that after a variable resting period, the formation of oogonia to vitellogenesis takes ∼3 days, investing ∼8% (4–14%) of weight-specific carbon body weight to reproduction (lipid approach) with an average interbrood period of 10 days (range: 7–26 days, estimated by three distinct methods). About 22% of the ovigerous females in the metanauplius stage show gonad development in vitellogenesis, likely spawning between 7 and 9 days. The rest of the female population have an interbrood period that is considerably >10 days. Embryonic development in the ovigerous sac last <3 days (16°C), hatching always as nauplius (usually 100% hatching success); the metanauplii are released from the ovigerous sac in a median of 5 days after spawning. Although sac-spawning euphausiid species may have comparatively lower total fecundity than broadcast-spawning species, they seem to have relatively similar reproductive effort and higher hatching success that increases larval recruitment rates, compared to similar size temperate broadcast-spawners. This partially explains why sac-spawners of the genera Nyctiphanes, Nematoscelis, and Pseudeuphausia are numerically dominant euphausiids in several highly eutrophic temperate, subtropical, and tropical ecosystems. N. simplex males have a continuous spermatogenesis after they attain size at first maturity; continuously allocating ∼5.4% of weight-specific carbon to reproduction, results that are significantly different than previous assumptions that euphausiid male spermatogenesis is energetically insignificant. [Copyright &y& Elsevier]

The California butterfly ray Gymnura marmorata is frequently caught by artisanal fisheries in north-western Mexico (Baja California Sur; BCS). The aim of this study was to estimate reproductive characteristics and describe the micro and macroscopic reproductive structures of female and male G. marmorata. Sampling was carried out at two fisheries landing sites located on the west coast BCS, from 2008 to 2012. The largest disc width (W D ) ever recorded for this species was 131.0 cm and females were larger than males. The male sample was composed exclusively of adult specimens, with a median size at 50% maturity (W D50 ) estimated at 44.9 cm W D . For females, size at onset of maturity was estimated at 63.0 cm W D ; W D50 , at 64.7 cm W D ; and size at pregnancy at 80.1 cm W D . Gonadal asymmetry was observed for the first time in this species. Indeed, in males only the left testis was functional (testicular asymmetry), while in females, only the left ovary was functional (ovarian asymmetry)., (© 2019 The Fisheries Society of the British Isles.)

This study found that the reef stingray Urobatis concentricus presents a matrotrophic aplacental viviparous reproduction with yolk sac and trophonemata formation. Growth of ovarian follicles occurs asynchronously and continuously with fecundity of three embryos per female. A maximum size of 58·4 cm total length and 37·6 cm disc width was recorded, corresponding to a mature female of 3 or 4 years of age., (© 2017 The Fisheries Society of the British Isles.)