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This study evaluated the influence of rearing system (cultured vs. wild rearing systems), and fish sex on carcass and flesh traits of A. rivulatus, raised in Ecuador. Three hundred mature specimens from A. rivulatus were captured, 150 from each origin. Slaughter yield and dress-out resulted similar for both rearing system, and average fillet yield for cultured fish was significantly higher than for wild fish, while cooking loss was significantly lower. Dress-out was significantly higher in females. Significant differences were found in wet percentage, ash, fat and protein content in both rearing systems, but only wet percentage was significantly affected by sex. Palmitic, oleic and arachidonic acids had the maximum percentage of saturated (SFA) and mono/poly unsaturated (MUFA/PUFA) fatty acids, respectively. In cultured and wild fish, differentiations were also found in PUFA/SFA, docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA), atherogenicity (IA), and thrombogenicity (IT) indices, along with P, K, Mg, Cu and Fe. Sex and rearing system significantly influenced most of the analyzed characteristics of carcass and flesh of A. rivulatus. Fillet high yield and its proximate composition categorize A. rivulatus as a suitable food. These results provide valuable nutritional information about native species for consumers in Ecuador. [ABSTRACT FROM AUTHOR]

Highlights • Markedly seasonal cuttlefish trap fishery performed in southern Portugal. • Locally important socio-economic activity during spring and summer. • Catches with male-biased sex ratios and females larger and heavier than males. • Most catches accomplishing the minimum conservation reference size (MCRS). • Highly sustainable small-scale fishery and low impacting artisanal fishing gear. Abstract The present study reports a detailed description of the catches of cuttlefish (Sepia officinalis) in the trap fishery performed seasonally off the Algarve coast (southern Portugal). A total of 86 fishing surveys were performed during the fishing season (May–September) from 2009 to 2014, on sandy bottoms at bathymetrics ranging from 8 to 10 m depth. During the whole study period, fishing operations involved 6311 cuttlefish traps with a gear catch rate of 37% (frequency of traps with cuttlefish) and a mean of 0.9 S. officinalis caught per trap. A total of 5883 S. officinalis (1424.0 kg) were caught, being only recorded 282 dead individuals (mortality rate of 4.6%). The mean fishing yield (standardised CPUE's in number and weight) was 46.6 individuals and 11.3 kg 50 traps−1. Overall, males (n = 3188) outnumbered females (n = 2695), producing a significant male-biased (1 M: 0.85 F) sex ratio. On average, females were significantly larger and heavier (124.4 ± 22.9 mm ML; 253.1 ± 148.8 g TW) than males (121.9 ± 24.0 mm ML; 230.7 ± 143.1 g TW). Accordingly, the length-frequency distributions displayed significant gender differences, with 89.6% of females and 85.8% of males accomplishing the MCRS (100 mm ML). This markedly seasonal, highly sustainable and low impacting small-scale fishery constitutes a locally important socio-economic activity during spring and summer. Undamaged catches and highly fresh individuals further contribute to the considerable price reached by S. officinalis caught using this artisanal fishing gear. [ABSTRACT FROM AUTHOR]

The parameters of length-weight relationship Labeo fimbriatus were estimated from Vani Vilasa Sagara Reservoir, Chitradurga district, Karnataka. The regression co-efficient of male was found to be lower than female. From this observation it may be opined that female gained more weight in length compared to male. Even though 'b' values are around '3', it was found that there was significant difference between sex. Hence, separate equations for both the sex were derived. During 2013-14 the equations were for male 0.0182 L2.9427 and for females 0.0158 L2.9808 likewise, during 2014-15, the equations were W = 0.0197L2.8782 and 0.0161L2.9857 for male and female, respectively. Data on seasonal variation in condition factor (Kn) of both male and female during both the years of the study showed that the values were more or less similar in both the sex, indicating almost identical metabolic activity in male and female which may be attributed to gonadal development and high feeding intensity. The Kn values were observed in the range of 0.9902 to 1.0653 for males and 0.9996 to 1.0686 for female in different seasons. These parameters are useful to evaluate the wellbeing population, their biology for scientific management of fisheries and stock assessment. [ABSTRACT FROM AUTHOR]

Highlights • Greater amberjack sex ratio in the Gulf of Mexico may differ from 1:1. • Sex-specific fishing mortality rates can theoretically alter amberjack sex ratios. • Altered sex ratios influence could influence population dynamics of amberjack. • Incorrect sex ratio assumptions could lead to management issues. • Should incorporate a range of realistic sex ratios into future stock assessments. Abstract The US Gulf of Mexico stock assessment of greater amberjack Seriola dumerili assumes a 1:1 male:female sex ratio. However, the observed sex ratio in the landed catch is 1:1.8, and for fish >1 m fork length is 1:2.4. To theoretically explore whether this female-skewed sex ratio may arise due to differential fishing mortality between the sexes, we used a sex-specific age- and size-based model to investigate how different fishing mortality rates could create a female-skew in the landed catch as well as its subsequent effects on reproductive potential. When fishing mortality rates in the model were equal between the sexes, the sex ratio of the landed catch was approximately 1:1 for all legal-sized fish, and approximately 1:2.4 for fish >1 m FL. However, reproductive potential decreased in comparison to the corresponding scenario with equal fishing mortality rates when fishing mortality rates between the sexes were changed to create the 1:1.8 sex ratio observed in the landed catch. This modeling study demonstrates one possible route that could explain the female-skewed sex ratios observed in the landed catch, and indicates that sex ratio values other than 1:1 should be considered in future stock assessments for Gulf of Mexico greater amberjack. [ABSTRACT FROM AUTHOR]

Intraspecific genetic admixture occurs when previously separated populations within a species start interbreeding, and it can have either positive, negative, or neutral effects on reproductive performance. As there currently is no reliable predictor for the outcome of admixture, an increased knowledge about admixture effects in different species and populations is important to increase the understanding about what determines the response to admixture. We tested for effects of admixture on F1 offspring quality in three subpopulations of pike (Esox lucius). Gametes were collected in the field, and eggs from each female were experimentally fertilized with milt from a male from each population (one "pure" and two "admixed" treatments). Three offspring quality measures (hatching success, fry survival, and fry length) were determined and compared between (a) pure and admixed population combinations and (b) the sex‐specific treatments within each admixed population combination (based on the origin of the male and female, respectively). The results suggested that although there were no overall effects of admixture on offspring quality, the consequences for a given population combination could be sex‐specific and thus differ depending on which of the parents originated from one or the other population. All offspring quality traits were influenced by both maternal ID and paternal ID. Sex‐ and individual‐specific effects can have implications for dispersal behavior and gene flow between natural populations, and are important to consider in conservation efforts. We tested for effects of genetic admixture on offspring quality in three natural subpopulations of pike (Esox lucius) in an artificial fertilization experiment with a common garden setup. The results revealed that although there were no overall effects on offspring quality on the population level, the effects for a given combination of populations could differ depending on which of the parents originated from one or the other population. Such sex‐specific effects have implications for dispersal behavior and gene flow between natural populations, and are important to consider in conservation efforts. [ABSTRACT FROM AUTHOR]

Abstract: Culture of the Chinese mitten crab Eriocheir japonica sinensis has become a large industry in China because of improved hatchery techniques in the past two decades. In this study, we investigated the reproductive potential of individual male crabs in a local pond‐reared breeding stock [with a 2.5:1 female‐biased sex ratio] to assess the current broodstock management. Relative to virgin (unmated) males, vasa deferentia of the removed pond males markedly changed and some even showed extremely sperm‐depleted conditions, such as wizened tube and accessory gland mass and no spermatophores and/or a small quantity of seminal fluid in the lumen. According to calculating individual VSIs, these males could be divided into two groups as small (≤139 g/ind., mean VSI = 2.82%) and large males (>139 g/ind., 1.70%). Combined with the baseline value (2.08%), approximately 50% male (more than 90% from large males) could be graded as “depleted.” These findings strongly indicated that the current broodstock management had a risk of sperm limitation. However, given that “depleted” large males had a relatively high seminal replenishing capacity, and posthatch females always retained a certain amount of sperm load, we could further postulate that other ways should be adopted to offset party of individuals excessive consumption of sperm load at a broodstock level. Thus, we might optimize such an artificial breeding stock and adjust a female‐biased sex ratio to 4:1–5:1 by selecting a large male broodstock (>150 g/ind.) to reduce the number of male and increase female to change the entire broodstock structure while maintaining its density. [ABSTRACT FROM AUTHOR]

A wide range of ecological and environmental factors influence metal bioaccumulation in fish. Studies of mercury and other metal contaminants in invasive Indo-Pacific lionfish are limited, yet consumption of the invasive predator is increasingly utilized as a management strategy. In this study, we examined the effects of body size, body condition, sex, trophic level, carbon source, diet, depth and capture location on mercury concentrations in lionfish collected from Curaçao. In addition, we examined whether or not a local petroleum refinery is the source of metal contamination in lionfish. Mercury concentrations ranged from 0.008 to 0.106 mg/kg and we found no effect of the petroleum refinery on metal bioaccumulation in lionfish. Low concentrations of metal contaminants indicate lionfish from Curaçao are safe for human consumption. [ABSTRACT FROM AUTHOR]

This study presents data and estimates reproductive parameters of the sailfish Istiophorus platypterus (Shaw, 1792) in the western Atlantic, useful for future stock assessments of the species in the Atlantic Ocean. During the period 2006-2011, a total of 1132 fish were sampled by scientific observers on board Venezuelan and Brazilian longline vessels and from artisanal fisheries based out of Cumaná, Puerto La Cruz and Playa Verde, Venezuela and Cabo Frio, Rio de Janeiro, Brazil. The ovaries of 543 females were classified into five ovarian development phases based on microscopic analysis of the most advanced group of oocytes. Generalized additive models were applied to the gonadal index and sex ratio data in order to assess spatio-temporal trends of the reproductive activity and identify the spawning areas. Space-time effect was a significant factor contributing to changes in sex ratio and reproductive activity. Spawning activity was observed in two distinct areas. On the south-east Brazilian coast spawning peaked during December-February, while in the south-eastern Caribbean Sea spawning occurred between March and September, with its peak in March and April. Using a Bayesian approach, size at 50% maturity was estimated to be 146.12 cm (credibility interval of 95%, 138.45-152.09 cm). Batch fecundity ranged from 436,800 to 2,492,500 hydrated oocytes per female. This study confirms multiple aggregation spawning for this species in the western Atlantic Ocean. [ABSTRACT FROM AUTHOR]

The paper presents the results of research on the reproductive biology of Syngnathus abaster - a species distributed in Çandarlı Bay. For this purpose, seine nets were collected from a depth of 0.5-2 m in 15 minute periods between April 2013 and March 2014, and a total of 185 individuals were sampled. It has been determined that 94 individuals (50.81%) were females, 79 were males (42.70%) and 12 were immature (6.49%). The sex ratio was 1:0.84. The average length values in female, male and immature individuals were 111.5±7.35, 109.9±11.08 and 79.8 ± 5.30 mm, respectively. The maximum mean surface water temperature is in spring and summer seasons. When Gonadosomatic Index (GSI%) values were examined, the spawning period of the species was indicated as spring and summer. Three groups of species were identified as maturing (diameter: 0.61-1.20 mm), mature (diameter: 1.21-1.70 mm) and hydrated oocytes (diameter: 1.71-2.10 mm) in ovaries of female individuals. The number of eggs in the brood pouch of pregnant male shes was on average 48 (mean ± SD = 48 ± 14.09 eggs, range: 23-78 eggs). The hydrated oocyte/total length relationship was: y = 0.8651x - 84.332 (n = 14, r² = 0.64) and the number of eggs/total length relationship in the brood pouch of pregnant males was: y=1.0168x - 67.715 (n=33, r2=0.58). [ABSTRACT FROM AUTHOR]

We applied essential fatty acids as a biomarker to experimentally test the effects of a fish-mediated trophic cascade on calanoid copepod nutritional state and functional traits in north-temperate freshwater ponds. A whole-pond experiment was conducted where young-of-the-year brook trout (Salvelinus fontinalis) were introduced into three natural, fishless ponds with no previous history of fish introduction, and compared with four similar naturally fishless ponds. We unexpectedly found no effect of the fish-mediated trophic cascade on copepod population nutritional state and abundance, despite enhanced phytoplankton resources in fish-stocked ponds. While salmonids increased individual female copepod fecundity, the fish also reduced gravid copepod female abundance and altered copepod population sex ratios in favour of males. Fish predation likely influenced the overall nutritional state of calanoid copepod populations by expenditure of key lipids in male copepods through increased activity linked to female mate limitation, and selective predation on gravid female copepods. Therefore, the positive effects of the fish in enhancing the essential fatty acid content of phytoplankton communities via nutrient additions were not sufficient to over-ride the negative effects of fish predation on copepod population nutritional state and abundance. [ABSTRACT FROM AUTHOR]

Abstract: Most behavioral studies on hermaphroditic fishes have focused on small‐sized species, which are tractable for research. Although many species of large hermaphroditic fishes are important fishery resources, their proximate mechanisms (visual, chemical and/or behavioral cues) in the social regulation of sex change have not been determined. Determination of these would inform resource management and aquaculture. In order to get closer to understanding the proximate mechanisms underlying the social regulation of female‐to‐male sex change in large hermaphroditic fishes, this study reports situations that induced female‐to‐male sex change in black‐spot tuskfish, Choerodon schoenleinii, a species of large protogynous fish, in massive laboratory tanks. The situations differed in the possibility of male‐to‐female tactile contact and in the group sex ratio, enabling us to infer plausible proximate mechanisms underlying sex change induction. Tactile contact between individuals is suspected to be closely related to the incidence of female‐to‐male sex change in C. schoenleinii. Visual and chemical cues alone may be insufficient to inhibit such sex changes. Male‐to‐female tactile contact may have an important influence on female‐to‐male sex change, i.e., inhibition of this sex change, in this species. The effect of sex ratio of a social group on the incidence of sex change may be due to the relative frequency and intensity of male tactile contact with each female, which may vary with the number of females. In the absence of a dominant male, tactile contact among females may affect the incidence of sex change, as well as determine which individuals change sex. [ABSTRACT FROM AUTHOR]

The aim of the present study is to provide morphometric relationships for the Mediterranean wide-eyed flounder Bothus podas (Delaroche, 1809), to identify possible sexual dimorphism, and to determine the feeding habits and the functional role of the species in the ecosystem. Sampling was carried out during a trawl survey off the coast of northern Crete in early May of 2015. A total of 425 specimens were examined (175 males and 250 females; total length (TL) range: 6.2-13.5 cm and 6.0-15.1 cm, respectively). The relationships between TL and weight, interorbital space (IO), body height (BH), and mouth dimensions (horizontal mouth opening: HMO, vertical: VMO mouth opening, and mouth area: MA) were all significant (P < 0.05) and of power types. The estimated value of the exponent b of the length-weight relationship (LWR) for sexes combined was 2.923. Sexual dimorphism was exhibited for the relationships between TL and IO, BH, VMO, HMO, and MA, whereas this was not true for the LWR. The diet spectrum of B. podas includes mainly benthic invertebrates and to a lesser extent small benthic fishes. On one occasion, an individual larva of Fistularia commersonii was recorded in the stomach contents of a male, and this is the first report of any predator of this Lessepsian invader in the Mediterranean. [ABSTRACT FROM AUTHOR]

Sex differentiation is a profitable technique in crayfish aquaculture. Most of the studies have focused on sex differentiation in crayfish by ablation or implantation of androgenic glands. There is no research on sex differentiation using hormones in crayfish. In the present study, the effects of 17β-estradiol (E2) injections (10−7 mol/crayfish) to females and baths (50 μg 17β-estradiol/L) to pleopodal eggs and stage1, 2, and 3 juveniles on the feminization of freshwater crayfish,Astacus leptodactyluswere investigated. Results showed that E2 injection to females, bath to pleopodal eggs and bath to stage 1, 2, and 3 juveniles increased feminization rate significantly (p < 0.05) in comparison to the control inA. leptodactylus. Best feminization rate (male to female, 0.25:1) was observed after hormonal injection to the females combined with application of both for their both pleopodal eggs and stage 1, 2, and 3 juveniles. In conclusion, it is possible to obtain 75% femalesA. leptodactylusby E2 injection to females and bath to pleopodal eggs and stage 1, 2, and 3 juveniles. However, future studies are needed to investigate the mechanism of E2 in crayfish feminization and the sexual development of juveniles obtained from feminization. [ABSTRACT FROM AUTHOR]

For the first time, the present study reports the life-history traits, comprising length-frequency distribution (LFD), sex ratio (SR), length-weight relationships (LWRs), condition factors (CFs), and relative growth ( W ), of Clupisoma garua in the coastal waters of Bangladesh. A total of 150 specimens ranging from 8.60 to 25.20 cm total length (TL) and 4.26 to 128.80 g body weight (BW) were collected using traditional fishing gear from August 2013 to July 2014. The overall sex ratio of males to females in the study did not differ significantly from the expected value of 1:1 (χ =0.96, P <0.05) but there were significant sex differences ( P <0.05) in the intercepts and slopes of graphs characterizing traits in C. garua. The calculated b values for the LWRs were 2.955, 2.893 and 2.927 for males, females and combined sexes, respectively, and there was negative allometric growth in all cases ( b <3). The condition factors ( K , K , K ) and relative growth ( W ) also did not differ significantly ( P <0.05) between the sexes. This study provides a useful tool for fishery specialists to evaluate the relative condition of fish and to initiate early management strategies and regulations for the sustainable management of the remaining stocks of this species in the entire coastal region of southern Bangladesh. [ABSTRACT FROM AUTHOR]

Samples (6404) of Nile perch were collected monthly from commercial catches between June 2014 and June 2015. The total length (cm), weight (g) and sex of fish were all determined in the field, with 3771 (59%) being male and 2059 (32%) being female fish, for an overall sex ratio of 1.83:1.00 (male: female). The average length and weight for all fish were 55.38 ± 0.14 cm TL and 2355.10 ± 22.30 g, respectively. The size of male fish ranged from 15.5 to 128.5 cm TL and weighed between 190 and 25 000 g, whereas that of female ranged from 21.0 to 130.0 cm TL and weighed between 124 and 25 800 g. The value of the regression slope b of the length-weight relationship was equal to 3.04. The mean (± SD) condition factor for all fish was 1.23 ± 0.13. The condition factor was different in the length groups, with the highest (1.32 ± 0.13) and lowest (1.12 ± 0.20) values recorded in length groups 100-110 and <30 cm TL, respectively. The highest and lowest condition factors were recorded between January and March, respectively. The length-weight relationship and condition of Nile perch in Lake Victoria have deteriorated greatly, this finding being linked to the reduction of its prey species in the lake. [ABSTRACT FROM AUTHOR]

Background. We present length-weight relations (LWR) and describe the reproductive biology of five species of coral reef fishes from Papua New Guinea (PNG). Each of these species are targeted by artisanal- and smallscale commercial fisheries throughout the country. As such the purpose of this study was to provide baseline reproductive information that can be used for future evaluation and management of the fishery. Materials and methods. We used recently developed methods for rapid, low-cost, on-site, histology-based reproductive analysis that requires minimal research infrastructure. These methods use standard techniques (e.g., plastic embedding) that have been modified such that work can be conducted in remote field settings without electrical service. We studied the following fish species: the teardrop threadfin bream, Nemipterus isacanthus (Bleeker, 1873); the dash-and-dot goatfish, Parupeneus barberinus (Lacepède, 1801); the blue sea chub, Kyphosus cinerascens (Forsskål, 1775); the striated surgeonfish, Ctenochaetus striatus (Quoy et Gaimard, 1825); and the orange-lined triggerfish, Balistapus undulatus (Park, 1797). Results. In all species, length was an approximately cubic function of weight. Female B. undulatus mature at a smaller size than males; in the other four species males mature at a smaller size. Nemipterus isacanthus, K. cinerascens, C. striatus, and B. undulatus are gonochores. Females are rare or absent in the largest size classes of N. isacanthus, P. barberinus, C. striatus, and B. undulatus. For P. barberinus and B. undulatus, size classes well below maximum observed size are responsible for the majority of egg production. Conclusion. Our results differed markedly from those of macroscopic and data-deficient approaches and may help to avoid unnecessary management actions. Further, an emergent pattern challenges a current paradigm in reef-fish conservation and management; contrary to a general assumption for many reef-fish species, the largest size classes of at least three species did not have the highest per-capita fecundity. Because females were rare or absent in the largest size classes, smaller fish are responsible for the majority of egg production. Thus, for coastal communities dependent upon reef fishes for sustenance, our results suggest it may be easier to balance food needs and conservation by fishing across a broad size range. Further, because of diminished concern about targeting the larger size classes commonly assumed to be responsible for the majority of egg production, doing so will simultaneously promote adequate reproductive output. [ABSTRACT FROM AUTHOR]

Fishing pressure is a significant driver of the demography of exploited fish populations. Here, we examine temporal patterns in the demography of king threadfin ( Polydactylus macrochir ), a large, protandrous teleost, in Queensland’s south-eastern Gulf of Carpentaria, Australia, between two periods: 1986–1990 (Period 1) and 2007–2009 (Period 2). Significant age truncation was evident from Period 1 (max age = 14 years, modal age = 5 years) to Period 2 (max age = 8 years, modal age = 3 years). Fish >5 years constituted 58% of the catch in Period 1, and less than 4% of the catch in Period 2. Length and age at sex change differed considerably between periods. In Period 1, the relationships between length and sex ratio and age and sex ratio were best described by a logistic model with 50% of the population changing sex to female at 889 mm fork length and at 6.3 years of age. In Period 2, there were substantially more females in small length and younger age classes with no obvious length or age at which sex change occurred. The predicted mean asymptotic length ( L ∞ ) from the best-fit models of growth was 361 mm greater in Period 1 than in Period 2, while the growth rate ( K ) was more than twice as high in Period 2 than in Period 1. Fishing mortality during Period 2 was estimated to be 2–3.5 times higher than that of natural mortality ( M ) and 2.6–5.4 times higher than that of Period 1, depending on the maximum age used to calculate M . No significant trends were evident in total annual rainfall or air temperature in the region over the study period, suggesting the observed changes in demography were not related to contrasting patterns in rainfall or temperature between sampling periods. These results suggest that heavy fishing pressure has likely had a profound effect on the demography of P . macrochir in the study region over a period of approximately 20 years, with the use of gillnets resulting in the selective removal of larger, older, female P . macrochir and subsequent reductions in age structures and sex change schedules. Accordingly, management intervention is urgently required to reduce fishing pressure and restore the natural demography of the population. [ABSTRACT FROM AUTHOR]

This osteological survey of 249 specimens of Brevimyrus niger ranging in size from 44 to 137 mm standard length ( LS) demonstrated that developmental changes in anal-fin morphology can serve as a predictor of sexual maturity in this species. Anal-fin ray bases begin to expand when fish reach c. 90 mm LS at which size and above there were roughly equal numbers of individuals observed with expanded and unmodified anal-fin bases, reflecting a 1:1 sex ratio. [ABSTRACT FROM AUTHOR]

To assess the repeatability of an ecological study, this study both partially replicates and extends a previous study on the site fidelity and homing ability of two abundant and ecologically important species of rocky intertidal sculpin fishes, Oligocottus maculosus and Oligocottus snyderi. A traditional mark and recapture approach was utilized and found that both of these species display high site fidelity to a home range of tidepools and homing ability to these pools, confirming the findings of previous work. Unlike the previous study, however, there was no effect of body size on homing ability and a modelling approach that incorporates encounter probability provided evidence for a sex effect on homing ability. In addition, this study extends the maximum homing ability of O. snyderi to 179 m and O. maculosus to 218 m, which were the maximum displacement distances for each species in this study, suggesting they may be capable of even greater homing distances. This work, however, finds that homing success was negatively related to displacement distance. These findings suggest adult sculpin populations are likely to be highly sub-structured geographically, possibly contributing to the exceptionally high species richness of the group. [ABSTRACT FROM AUTHOR]

The sex ratio is an important trait of natural populations and a key parameter for assessing the reproductive potential and stock status of exploited fish populations. In fisheries research, knowledge on spatial and temporal sex ratio variation can inform on the capacity of a population to support exploitation and environmental changes. Blue whiting (Micromesistius poutassou) shows sexual growth dimorphism after maturation, with females achieving greater lengths than males. The main goal of this work was to investigate seasonal patterns in the blue whiting sex distribution, size structure and condition in three areas along the Portuguese coast (north, southwest and south), based on bottom trawl surveys performed in autumn and winter between 1998 and 2015. Smaller blue whiting (12-24 cm) were found in shallow areas down to 250-300m while larger individuals (>24 cm) were spread deeper down to 400-500 m. Condition factor Fulton K differed significantly between seasons in all the areas (F = 11.72; p-value <0.001) and between sexes (F = 6.14; p-value <0.05). The proportion of females changed between autumn and winter (x²(1) = 4.38, p = 0.03) and across depths (x²(1) = 4.73, p = 0.03). Thus, this study revealed seasonal and depth variations in the blue whiting sex ratio along the Portuguese coast. [ABSTRACT FROM AUTHOR]

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Assortative mating based on ecologically divergent traits is a major driver of speciation among three-spined sticklebacks, however, little is known about reproductive isolation and variations in courtship behaviour among nine-spined sticklebacks. Here we demonstrate assortative mating and divergent courtship behaviours between two cryptic species of nine-spined sticklebacks using nochoice mate trials and kinematic analyses. Strong assortative mating was demonstrated in our tank experiments, highlighting the importance of prezygotic reproductive isolation in these species. Kinematic analyses showed that the freshwater type exhibited aggressive courtship behaviour with frequent 'Attacking' and spent more time exhibiting displacement activities. In contrast, the brackish-water type demonstrated a higher frequency of the 'Zigzag-dance' and 'Nest-showing'. Our study highlights the value of nine-spined sticklebacks as a comparative system for the study of speciation and paves the way for future studies on the role of courtship behaviours and assortative mating in the evolution of sticklebacks. [ABSTRACT FROM AUTHOR]

Stock-specific migration-timing and relative abundance of exploited fish species are critical parameters to estimate for management of mixed stock fisheries. Here, we used parentage-based tagging (PBT) together with mixed stock analyses (MSA) to estimate stock-specific abundance and migration-timing in anadromous adult steelhead (Oncorhynchus mykiss) sampled at Bonneville Dam in the lower Columbia River. Results indicate that natural-origin steelhead was represented by 11 of 13 possible stocks found throughout the Columbia-Snake river basins, while hatchery-origin steelhead was primarily composed of five stocks from the Snake River drainage. Further, migration-timing differentiated stocks and allowed categorization of early, intermediate, and late migrating stocks. Analyses of age and length data for these stocks also showed that late-arriving fish were larger due to older age and originated primarily from the Clearwater River, South Fork Salmon River, and Dworshak Hatchery, all from the Snake River drainage. Sex ratios tended to be skewed towards females and ranged from 51.5 to 68.9% for hatchery stocks and 60.5-71.8% for natural-origin stocks. This suggests that anadromous migration is favored by females while males are more likely to residualize in freshwater. Overall, this study demonstrates how the use of PBT in MSA can reveal important stock-specific differences in migration-timing and relative abundance and provides critical information for management of mixed stock fisheries. [ABSTRACT FROM AUTHOR]

In salmonids with partial migration, females are more likely than males to undergo smoltification and migrate to the ocean (vs. maturing in freshwater). However, it is not known whether sex affects survivorship during smolt migration (from fresh water to entry into the ocean). We captured wild steelhead ( Oncorhynchus mykiss) smolts in two coastal Oregon rivers ( USA) and collected fin tissue samples for genetic sex determination (2009; N = 70 in the Alsea and N = 69 in the Nehalem, 2010; N = 25 in the Alsea). We implanted acoustic tags and monitored downstream migration and survival until entry in to the Pacific Ocean. Survival was defined as detection at an estuary/ocean transition array. We found no effect of sex on smolt survivorship in the Nehalem River in 2009, or in the Alsea River in 2010. However, males exhibited significantly lower survival than females in the Alsea River during 2009. Residency did not influence this result as an equal proportion of males and females did not reach the estuary entrance (11% of males, 9% of females). The sexes did not differ in timing or duration of migration, so those variables seem unlikely to explain sex-biased survivorship. Larger males had higher odds of survival than smaller males in 2009, but the body size of females did not affect survivorship. The difference in survivorship between years in the Alsea River could be due to flow conditions, which were higher in 2010 than in 2009. Our findings suggest that sex may affect steelhead smolt survival during migration, but that the difference in survivorship may be weak and not a strong factor influencing adult sex ratios. [ABSTRACT FROM AUTHOR]

When competing for mates, males typically exhibit higher rates of intrasexual aggression and courtship than females. Operational sex ratio, represented here by adult sex ratio (ASR) as a proxy, is likely the best predictor of this competition, which typically increases between members of one sex as members of the opposite sex become rarer. Moreover, in populations subject to high predation, males often decrease mating competitive behaviour due to predation risk. We explored the combined effects of ASR and population of origin (low vs. high ambient predation risk) on mating competition in male and female wild-caught Trinidadian guppies. Both male and female aggression rates increased with ASR, but the increase for males was only significant in the low-predation population. In regard to male mating tactics, courtship propensity was unaffected by ASR, while the propensity to sneak increased at male-biased ASRs. Guppies from a high predation population had lower aggression rates than their low predation counterpart, but male courtship and sneaking attempts did not differ between populations. Surprisingly, females were just as aggressive as males when competing for mates. These results highlight the trade-offs between antipredator and agonistic behaviour, which may affect sexual selection pressures in wild populations. [ABSTRACT FROM AUTHOR]

Two key elements in the adequate, sustained exploitation of any fishery should be considered; the biological attributes of the species and how these vary over time and space. Research is needed to obtain a more thorough understanding of these effects, how they vary, and how they relate to environmental factors. For 17 years, biological information has been collected for Heterocarpus reedi (nylon shrimp) caught off central Chile (25–37 °S). Here, we analyze these data using generalized linear models and determine the factors responsible for changes in carapace length, body weight, maturity, and sex ratio. The environmental and alimentary conditions are better south of 32 °S, and this is probably associated with the better physical condition and reproductive attributes of H. reedi there. For example, individuals are larger, females are longer at first maturity (CL 50% ), and mature females are less prevalent. We outline a theoretical foundation that can guide future research on H. reedi . We also suggest that future conservation measures consider biological attributes within a spatial context. [ABSTRACT FROM AUTHOR]

Parrotfishes are an ecologically and commercially important teleost group whose grazing contributes to maintaining coral-dominated states on hermatypic reefs. However, overfishing has skewed sex ratios of Atlantic parrotfishes because fishing has disproportionate impacts on larger individuals, and males are generally larger than females. Whether protection from fishing may allow sex ratios to return to equilibrium is unknown, as fishing can induce irreversible ecological and/or evolutionary shifts. Bermuda banned trap fishing in 1990, creating a unique opportunity to analyse long-term responses of Atlantic parrotfishes to release from fishing. We found that sex ratios of four common parrotfishes were initially skewed, with male proportions ranging from 0.04 to 0.18. However, male proportions rebounded within 3-4 yr, equilibrating at values ranging from 0.36 to 0.54, similar to those reported at unfished sites in the region. Our results are encouraging for regional efforts to recover lost grazing function by restoring overfished herbivore populations. [ABSTRACT FROM AUTHOR]

Growth variability within individuals and among groups and locations and the phenomenon of summer growth reduction has been described for juvenile flatfish in a variety of European coastal areas whereby the underlying causes still remain elusive. Potential mechanisms were tested for juvenile plaice Pleuronectes platessa L. in the western Dutch Wadden Sea, by analysing published and unpublished information from long-term investigations (1986–present). Growth variability did occur and could be explained by differences induced by environmental variability (water temperature), and by non-genetic irreversible adaptation and sex. Dynamic Energy Budget analysis indicated that especially sexually-dimorphic growth in combination with variability in sex ratio could explain most of the variability in growth and the increase in the range of the size of individuals within the population over time. Summer growth reduction was not only observed among 0-group plaice in the intertidal, but also in the subtidal and tidal gullies as well as among I- and II-group plaice. Intraspecific competition for food was not detected but some support for interspecific competition with other predators was found. Also resource competition (due to crowding) with the other abundant epibenthic species (0-, I- and II-group flounder Platichthys flesus ; the brown shrimp Crangon crangon ; the shore crab Carcinus maenas ; the goby species Pomatoschistus minutus and Pomatoschistus microps ) could not explain the summer growth reduction. The observed growth reduction coincided with a decrease in stomach content, especially of regenerating body parts of benthic prey items. It is hypothesised that macrozoobenthos becomes less active after the spring phytoplankton bloom, reducing prey availability for juvenile plaice in summer, causing a reduction in food intake and hence in growth. [ABSTRACT FROM AUTHOR]

The evaluation of the growth patterns and reproductive strategies of fish species are vitally important for the understanding of their biology and the management of stocks. The present study focused on the Amazonian electric eel ( Electrophorus electricus), which is capable of producing an electrical discharge of up to 800 V. Specimens were collected on a monthly schedule from a floodplain in the eastern Amazon basin. The gonads of these specimens were examined, and the sex ratio, growth parameters, population structure, body size at first gonadal maturation, and the gonadosomatic index were determined. A balanced sex ratio was found. Males were larger than females, and both sexes presented isometric growth, which is unusual in species with an elongated anatomy. This isometry may be related to the reduction of the coelomic cavity, and its position near the head. The spawning period coincided with the start of the rainy season, and continued until high water, with the variation in gonadal development following the fluctuations in precipitation and river water levels. The asymptotic body length in both sexes was relatively large, and was inversely related to the growth coefficient ( k), with a slower growth rate being recorded in the males. Mortality rates were relatively low in comparison with most species of tropical fish. The larger size of the male may be related to their role in parental care, and sexual selection on the part of the females. These findings may be important for the management of wild stocks, as well as captive rearing. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine whether the timing of elevated cortisol levels in adult female rainbow trout Oncorhynchus mykiss, achieved by silastic implants within the body cavity, had an effect on embryo viability. Cortisol-implanted fish experienced a significant increase in circulating levels of plasma cortisol compared with sham-implanted fish, and plasma cortisol remained elevated relative to sham-implanted fish for 4 months in each of the three treatment groups (0-4, 4-8 and 8-12 months). There were no significant differences in embryo viability, egg diameters or plasma 17β-oestradiol levels between the cortisol and sham-implanted treatments in any of the groups. There was a significant difference in the number of subfertile females (<80% embryo viability) when the three treatments were compared. The majority of the females (75%) implanted immediately postspawn (0-4 months) produced subfertile eggs, which was significantly higher than those treated 4-8 (33%) or 8-12 (17%) months postspawn. These results imply that silastic implantation can affect oocyte development, independent of plasma cortisol levels, leading to a reduction in embryo viability. [ABSTRACT FROM AUTHOR]

Using treatments that mimic high and low availability of reproductive males, it was found that female three-spined sticklebacks Gasterosteus aculeatus, previously shown to adjust their mate choices when male mates were rare, did not alter their reproductive investment strategies. These results suggest that plasticity in investment is perhaps limited by physiological requirements or dependent on relatively extreme mate availability regimes. The probability of becoming reproductive, number of clutches per season (per female), initial clutch size and mass and the timing of reproduction were all independent of the experience a female had with mate availability. This suggests that pre-copulatory plasticity in reproductive strategies may contribute more to variation in the strength and direction of sexual selection than reproductive investment in offspring. [ABSTRACT FROM AUTHOR]

In this study, two parthenogenetic events within a family of the whitespotted bambooshark Chiloscyllium plagiosum are reported. A captive female produced multiple parthenogens. Unexpectedly, a single specimen of a total of nine parthenogens displayed external claspers characterizing the male sex in chondrichthyans. Upon dissection, internal sexual organs of this specimen were malformed or absent; however, the presence of claspers in this study challenges the as yet assumed sex determination system in this shark species. Even more remarkable was that one of the female parthenogens reproduced asexually again producing viable offspring. As far as is known, this is the first genetically confirmed evidence for second-generation facultative parthenogenesis in vertebrates. These results support the evolutionary significance of parthenogenesis as an alternative to sexual reproduction. [ABSTRACT FROM AUTHOR]

Sex-biased dispersal is expected to homogenize nuclear genetic variation relative to variation in genetic material inherited through the philopatric sex. When site fidelity occurs across a heterogeneous environment, local selective regimes may alter this pattern. We assessed spatial patterns of variation in nuclear-encoded, single nucleotide polymorphisms ( SNPs) and sequences of the mitochondrial control region in bonnethead sharks ( Sphyrna tiburo), a species thought to exhibit female philopatry, collected from summer habitats used for gestation. Geographic patterns of mt DNA haplotypes and putatively neutral SNPs confirmed female philopatry and male-mediated gene flow along the northeastern coast of the Gulf of Mexico. A total of 30 outlier SNP loci were identified; alleles at over half of these loci exhibited signatures of latitude-associated selection. Our results indicate that in species with sex-biased dispersal, philopatry can facilitate sorting of locally adaptive variation, with the dispersing sex facilitating movement of potentially adaptive variation among locations and environments. [ABSTRACT FROM AUTHOR]

Growth, sex ratio, and reproduction of striped red mullet (Mullus surmuletus L.) were determined from 520 specimens collected in the northwestern Aegean coast of Turkey from September 2009 to July 2010. Total length ranged from 7.7 to 17.0 cm while weight varied between 3.50 and 58.9 g. According to the length-weight relationship, positive allometry was confirmed for both sexes. The sex ratio was skewed in favour of males (1:1.73). The monthly values of gonadosomatic index (GSI) of females indicated that spawning occurred mainly between April and September with a peak in July. Values of Condition factor (CF) and Hepatosomatic index (HSI) varied between 0.71-1.57 and 0.10-1.43, respectively. [ABSTRACT FROM AUTHOR]

Background: The role of microRNAs in gene regulation has been well established. The extent of miRNA regulation also increases with increasing genome complexity. Though the number of genes appear to be equal between human and zebrafish, substantially less microRNAs have been discovered in zebrafish compared to human (miRBase Release 19). It appears that most of the miRNAs in zebrafish are yet to be discovered. Results: We sequenced small RNAs from brain, gut, liver, ovary, testis, eye, heart and embryo of zebrafish. In brain, gut and liver sequencing was done sex specifically. Majority of the sequenced reads (16–62 %) mapped to known miRNAs, with the exception of ovary (5.7 %) and testis (7.8 %). Using the miRNA discovery tool (miRDeep2), we discovered novel miRNAs from the unannotated reads that ranged from 7.6 to 23.0 %, with exceptions of ovary (51.4 %) and testis (55.2 %). The prediction tool identified a total of 459 novel pre-miRNAs. We compared expression of miRNAs between different tissues and between males and females to identify tissue associated and sex associated miRNAs respectively. These miRNAs could serve as putative biomarkers for these tissues. The brain and liver had highest number of tissue associated (22) and sex associated (34) miRNAs, respectively. Conclusions: This study comprehensively identifies tissue and sex associated miRNAs in zebrafish. Further, we have discovered 459 novel pre-miRNAs (~30 % seed homology to human miRNA) as a genomic resource which can facilitate further investigations to understand miRNA-mRNA gene regulatory networks in zebrafish which will have implications in understanding the function of human homologs. [ABSTRACT FROM AUTHOR]

Squalus acanthias has been poorly studied in Uruguay, though reproductive studies have been carried out in Argentina in the decades of 1970-1980. The aim of this work was to analyze the population structure and the reproductive biology of S. acanthias along the Uruguayan continental shelf (south-western Atlantic Ocean) between 1995 and 2010. Total length (TL) ranged from 30-95 cm for females ( n = 1,323) and 25-81 cm for males ( n = 999). Significant differences in the TL frequency distributions between sexes and among seasons were detected, with abundances in the magnitude of up to 5,000 individuals/nm. Length at first maturity (TL) was 58.3 cm in males and 70.4 cm in females. Ovarian and uterine fecundity were 2-14 and 1-14, respectively, and both were positively correlated with maternal TL. Females with candled embryos were recorded in autumn. Embryo TL was significantly greater in winter, which is when parturition is likely occurring. Full-term embryos had a TL of 22-25 cm. Sex ratio of embryos was close to parity. Ovarian vitellogenesis was observed to be occurring concomitantly with gestation. [ABSTRACT FROM AUTHOR]

The influence of hatching date on the sex ratio of wild Gnathopogon caerulescens was examined. Cohorts reared from eggs collected in the early and middle parts of the spawning season showed almost balanced sex ratios, with female bias in some cohorts. Cohorts born later in the season mostly displayed male bias, and the mean proportion of males later in the season was significantly higher than in early- and mid-season cohorts. These results indicate that the sex ratio of G. caerulescens changes with the time of breeding, increasing along with the ambient water temperature of the lake. [ABSTRACT FROM AUTHOR]

Deania calcea ( n = 420) were collected from the catch of deep-water trawlers in the southern and eastern scalefish and shark fishery in southern Australia during the years 2008-2011. The total length ( LT) range varied between sexes, females being larger ( n = 264; 280-1530 mm) than males ( n = 156; 310-921 mm). The reproductive cycle in this population is non-continuous and asynchronous. The estimated LT at which 50% of males are mature is 807 mm and is 914 mm for females. Populations of D. calcea in higher latitudes appear to mature at a larger size than conspecifics in lower latitudes, in both the northern and southern hemispheres. Litters ranged from three to 10 embryos with a 1:1 sex ratio, but litter size does not increase with maternal LT. Deania calcea shows geographical variability in its biological parameters and gathering information on life-history traits of populations is vital to understand the trade-offs made by this species in response to environmental conditions and to predict intraspecific spatial differences. Such information is a basis for specific spatial management to protect populations from excessive fishing. [ABSTRACT FROM AUTHOR]

Sepia officinalis egg protection is ensured by a complex capsule produced by the female accessory genital glands and the ink bag. Our study is focused on the proteins constituting the main egg case. De novo transcriptomes from female genital glands provided essential databases for protein identification. A proteomic approach in SDS-PAGE coupled with MS unveiled a new egg case protein family: SepECPs, for ia officinalis gg ase roteins. N-glycosylation was demonstrated by PAS staining SDS-PAGE gels. These glycoproteins are mainly produced in the main nidamental glands. SepECPs share high sequence homology, especially in the signal peptide and the three cysteine-rich domains. SepECPs have a high number of cysteines, with conserved motifs involved in 3D-structure. SDS-PAGE showed that SepECPs could form dimers; this result was confirmed by TEM observations, which also revealed a protein network. This network is similar to the capsule network, and it associates these structural proteins with polysaccharides, melanin and bacteria to form a tight mesh. Its hardness and elasticity provide physical protection to the embryo. In addition, SepECPs also have bacteriostatic antimicrobial activity on GRAM- bacteria. By observing the SepECP / Vibrio aestuarianus complex in SEM, we demonstrated the ability of these proteins to agglomerate bacteria and thus inhibit their growth. These original proteins identified from the outer egg case ensure the survival of the species by providing physical and chemical protection to the embryos released in the environment without any maternal protection. [ABSTRACT FROM AUTHOR]

The reproductive biology of Caranx rhonchus (Geoffroy Saint-Hilaire, 1817) (Pisces, Carangidae) was studied in the Gulf of Gabès (Mediterranean Sea) from June 2004 to May 2006. Of 1313 individuals examined, 668 were females (50.9%) and 645 were males (49.1%). The overall sex ratio did not deviate significantly in favour of females (♀ : ♂ = 1.04 : 1). Monthly changes in the Gonado-Somatic Index ( GSI) showed a rapid increase from May to June and an extended very high level from June to September (4.43-3.47% for females and 3.35-2.61% for males), before declining sharply in October (down to 2.02% for females and 0.57% for males). The gametogenesis activity began with a pre-maturation phase from March to May, followed by a ripe-spawning phase from June to September. From the last days of July to the end of October, the gonads were in the spent and post-spawning stages. From November to early May, gonads were in the resting stages. The size at which 50% of the population reached sexual maturity was not significantly different between males and females : males attained sexual maturity at fork length FL50 = 161.20 ± 0.37 mm (n = 262), whereas females attained maturity at FL50 = 160.70 ± 0.23 mm (n = 296). The age of maturity for both sexes occurred at 2.1 years. [ABSTRACT FROM AUTHOR]

Examination of differences in contaminant concentrations between the sexes of fish, across several fish species, may show clues for important behavioral and physiological differences between the sexes. We determined whole-fish total mercury (Hg) concentrations of 25 male and 25 female adult burbot Lota lota captured in Lake Erie during summer 2011 and of 14 male and 18 female adult burbot captured in Great Slave Lake (Northwest Territories, Canada) during winter 2013. On average, females had 22 % greater Hg concentrations than males. This difference was probably not due to a greater feeding rate by females because results from previous studies based on polychlorinated biphenyl determinations of these same burbot indicated that males fed at a substantially greater rate than females. Based on our determinations of Hg concentrations in the gonads and somatic tissue of 5 ripe females and 5 ripe males, this difference was not attributable to changes in Hg concentration immediately after spawning due to the release of gametes. Furthermore, bioenergetics modeling results from previous studies indicated that growth dilution would not explain any portion of this observed difference in Hg concentrations between the sexes. We therefore conclude that this difference was most likely due to a substantially faster rate of Hg elimination by males compared with females. Male burbot exhibit among the greatest gonadosomatic indices (GSIs) of all male fishes, with their testes accounting for between 10 and 15 % of their body weight when the fish are in ripe condition. Androgens have been linked to enhanced Hg-elimination rates in other vertebrates. If androgen production is positively related to GSI, then male burbot would be expected to have among the greatest androgen levels of all fishes. Thus, we hypothesize that male burbot eliminate Hg from their bodies faster than most other male fishes and that this explains the greater Hg concentration in females compared with males. [ABSTRACT FROM AUTHOR]

Background. The turbot, Scophthalmus maximus (Linnaeus, 1758), is of high economical value in Turkey and its biological characteristics have hitherto not been studied in the South-western Black Sea. The purpose of this study was to determine the age and growth, length-weight relation, condition factor, sex ratio, age and length at fi rst maturity, and reproduction period of the turbot in the south-western Black Sea coast of Turkey. Materials and methods. Turbots were collected monthly in the south-western Black Sea coast of Turkey using bottom trawl and turbot gillnets. The fi sh samples were obtained between October 2004 and September 2005. Results. A total of 264 turbots were sampled and the age groups ranged from I to X (no individuals found at age group IX). Total lengths were between 14.0 and 70.0 cm, while weights varied from 34 to 5550 g. The length-weight relation for combined sexes was determined as W = 0.0085L3.1581. The von Bertalanffy growth equation parameters were: L∞ = 73.55 cm, k = 0.17 year-1, t0 = -0.12 year. The observed sex ratio (female : male) was 1 : 0.35. The length at fi rst maturity (L50) of the species was 20.38 cm for females and 24.68 cm for males (both at two years old). Monthly gonadosomatic index (GSI) values suggest the spawning activity extends from 15 April to late June. Conclusion. The legal fi shing season of the turbot, imposed in 2012, begins on 15 June. We recommend that this date should be postponed to 30 of June due to turbot's reproduction extending to late June. [ABSTRACT FROM AUTHOR]

Effects of dietary modified palm kernel meal (PKM) were investigated on growth performance, feed utilization, digestive enzyme specific activities, radical scavenging activity, carcass and muscle compositions, and muscle quality in sex reversed Nile tilapia ( Oreochromis niloticus ). The experiment was conducted in a completely randomized design with triplicate observations (4 treatments × 3 replicates × 8 fish per aquarium) during ten weeks of duration. The Nile tilapia (20.61 ± 0.15 g initial body weight and 10.45 ± 0.03 cm initial length) were fed with four isonitrogenous, isolipidic and isoenergetic diets containing 20% PKM, the treatments differing only in the nature of the PKM. It was either unprocessed (UPKM), water-soaked (SPKM), microwave-irradiated (MPKM), or water-soaked and microwave-irradiated (SMPKM). The fish fed with SPKM and SMPKM diets were superior in specific growth rate ( P < 0.05) and feed conversion ratio ( P > 0.05) when compared with the UPKM treatment. The digestion capacity of fish also slightly improved with both these dietary treatments, as indicated by the specific activities of trypsin and amylase ( P > 0.05). Only the fish fed with SPKM were adapted to digest lipids as compared to the control. Significant improvements in the radical scavenging activity of stomach were observed with MPKM and SMPKM treatments, but the levels were unaffected in the liver and intestine. No negative effects were found on scavenging activity in the three organs, in fish fed SPKM diet as compared to the control. The carcass and muscle compositions were closely similar across the four dietary treatments, with only small improvements from the SPKM and the SMPKM diets in terms of carcass moisture and ash, and muscle protein and RNA/protein ratio. No differences were observed in the enthalpy responses of muscle actin and myosin between the four dietary treatments, but an inducible protein peak was found only in the fish fed with SPKM. Overall, these findings indicate that water soaking or soaking followed by microwave irradiation improved the nutritional quality of the PKM-containing diet. Practically, the simple low-cost modification by water soaking has wide application potential in the administration of aquafeed. [ABSTRACT FROM AUTHOR]

Freshwater eelsAnguillaspp. are declining worldwide, and a major challenge is understanding why these panmictic species show contrasting patterns of intraspecific phenotypic variation and recruitment. We present results on studies of the American EelA. rostratato understand and discriminate the effects of origin and plasticity on growth and sex determination. We considered two separate growth and one length-at-age data sets. The first growth data set originated from a 34-month rearing experiment starting from the glass eel life stage to test the effects of origin, salinity, and density on growth and sex determination. The second growth data set originated from a shorter rearing experiment of 18 months starting at the yellow eel stage (around 3 years old) and compared transplanted individuals in Lake Ontario (LO) with natural migrants to the LO area. The third data set compared transplanted individuals in LO sampled by electrofishing with naturally migrating individuals. Sex ratios were identical for all origins and treatments in the long-term growth experiment (34–35% females). While male size distribution had little variability, certain female groups had a large variation in growth and presented fast- and slow-growing clusters. On the other hand, both cases of natural migrants to the LO area were consistent with being only slow-growing females. We found that wild individuals rearing in the LO area were nearly exclusively transplanted individuals and that males, as well as fast-growing females, were present. Even though the entire species is panmictic, these results support a role for spatially varying selection in explaining the phenotypic variation observed among regions and among individuals of the same region, and such factors must be considered for any successful management strategies of American Eel. Received December 17, 2013; accepted September 29, 2014 [ABSTRACT FROM AUTHOR]

In many species of Neotropical fishes, reproductive patterns are influenced by fluctuations in abiotic factors such as the flood pulse, temperature, and the physical-chemical characteristics of the aquatic environment. The present study describes the reproductive biology of the piranha, Serrasalmus gouldingi, in 'drowned' rivers of the region of the lower Anapu River in the eastern Brazilian Amazon basin. A total of 262 specimens were collected between July, 2010, and May, 2011, of which 113 were male and 149 female. The sex and maturity of these specimens were characterized histologically, and the sex ratio, gonadosomatic index, relative frequency of the different stages of maturity, size at first sexual maturation, and condition factor were determined and analyzed in the context of seasonal variation in river levels. Two major reproductive peaks were observed during the transitional flood and ebb periods, coinciding with a predominance of female specimens and higher frequencies of the mature, spawned, spent, and resting gonadal stages. Sexual maturity began at 12.24 cm in males and 16.33 cm in females. Positive allometric growth was associated with a decrease in the condition factor during the peaks of reproductive activity, which occurred prior to the principal fluctuations in local river levels. [ABSTRACT FROM AUTHOR]

The article discusses a study on zebrafish Danio rerio, and evaluating the influence of stocking density on fish sex and it induces masculinization. Topics include impact of evaluating breeding pair with female-biased sex ratios; effect of stocking density on sex ratio; and influence of density on sex in some genetically distinct families.

The sexual pattern ofDiplodus cervinus hottentotuswas investigated in southern Angola. Females were significantly smaller and found in greater numbers, with an adult sex ratio of 1.0:0.7, F:M. Histological observations of preserved gonads indicated that the species is a rudimentary hermaphrodite, possessing a non-functional bisexual ovotestis before maturation. Histological examination of five macroscopically staged ‘bisexual’ individuals revealed that they were functional males with residual ovarian tissue in the gonad, which had persisted from a juvenile bisexual stage. Although empirical population structure and macroscopic observations suggested protogyny, histological evidence suggested otherwise, confirming the need for the use of histology when diagnosing the sexual pattern of sparid fishes. [ABSTRACT FROM AUTHOR]

Individual growth is one of the main processes which drive the population dynamic and stock productivity. Many fish have differential individual growth by sex. Growth is affected by sexual development, which is frequently reached at different sizes in males and females. Differences in growth per sex after maturity produce different patterns in sex proportions-at-length in the population. If these patterns are the consequence of changes in life history parameters, sex ratio-at-length data can be expected to contain significant information on the population life history. In this paper I first explore how post-maturity changes in life history may shape these patterns in sex ratio-at-length; secondly I explore how these data may be used to estimate growth parameters and finally I discuss how this information may be useful for stock assessment purposes. I use European hake data and life history parameters to model expected sex ratios. The results suggest that reproductive energy allocation leads to a lower growth rate in male hakes than in females. Moreover the sex ratio-at-length may provide useful information for estimating growth parameters in dimorphic species if additional information from other sources is available. Finally, these data can easily be factored into stock assessment models to help provide a better estimation of growth parameters and mortality rates. This valuable, accurate and cheap biological information (sex ratio-at-length) may play an important role in population dynamic models and stock assessment for species with sexual size dimorphism. [ABSTRACT FROM AUTHOR]

Many populations have consistently biased adult sex ratios with important demographic and evolutionary consequences. However, geographical variation, the mechanisms, temporal dynamics and predictors of biased sex ratios are notoriously difficult to explain. We studied 334 wild populations of four species of African annual fish ( Nothobranchius furzeri, N. kadleci, N. orthonotus, N. rachovii) across their ranges to compare their adult sex ratio, its seasonal dynamics, interpopulation variation and environmental predictors. Nothobranchius populations comprise a single age cohort and inhabit discrete isolated pools, with wide-ranging environmental conditions (habitat size, water turbidity, structural complexity, predators), making them ideal to study adult sex ratio variation. In captivity adult sex ratios were equal. In natural populations, adult sex ratios were biased 1:2 toward females in three study species while N. kadleci had sex ratios at unity. There was a decline in the proportion of males with age in one species, but not in the other species, implying most severe male mortality early after maturation, declining later perhaps with a decrease in male abundance. In general, the populations at vegetated sites had relatively more males than populations at sites with turbid water and little vegetation. Selective avian predation on brightly coloured male fish likely contributed to female dominance and vegetation cover may have protected males from birds. In addition, an aquatic predator, a large belastomid hemipteran, decreased the proportion of males in populations, possibly due to greater male activity rather than conspicuous colouration. Alternative explanations for a sex ratio bias, stemming from male-male contests for matings, are discussed. We conclude that the effect of environmental conditions on adult sex ratio varies dramatically even in closely related and ecologically similar sympatric species. Therefore, difficulties in explaining the ecological predictors of sex ratio biases are likely due to high stochasticity rather than limited sample size. [ABSTRACT FROM AUTHOR]

The present study was carried out to assess the population structure, growth and condition factor of tench, between June 2012 and June 2013, in Mogan Lake. The age of T. tinca caught from Mogan Lake ranged between I to VII years. The sex percentage was determined as 50 % males, 42.92 % females and 7.08 % immature. Fork length of fish ranged from 9.2 cm to 36.5 cm and body weight of fish ranged from 9.4 g to 740 g. The von Bertalanffy growth equations were: Lt = 412.141 [1 - e-0.211 (t+1.82)] for females, Lt = 397.517[1 - e-0.174 (t+2.89)] for males and Lt = 384,001 [1 - e-0,235 (t+0,88)] for all individual; Wt = 1247.25 [1 - e-0.211 (t+1.82)] 3.1232 for females, Wt = 1208.94 [1 - e-0.174 (t+2.89)] 3.0293 for males and Wt = 1365,52 [1 - e-0,235 (t+0,88)] 3,1217 for for all individual. The condition factor was calculated as 1.69, 1.68 and 1.67 for females, males and for all individual, respectively. [ABSTRACT FROM AUTHOR]