Biology of santer seabream Cheimerius nufar (Val. 1830) from the Arabian Sea off Oman

The declining trend in the catches of santer seabream, Cheimerius nufar (Val. 1830), and sizable capture of immature and mature fish from the Arabian Sea at the coast of Oman have led to questioning the hypothesis that the fishery is in a state of decline due to inappropriate management. The lack of data on the basic biology and landing statistics for exploited fish species have made the management of fish resources in western Indian Ocean complicated. This paper presents data on the population biology of C. nufar in the Arabian Sea, with a view to contributing towards the development of management plans for a sustainable exploitation. A total of 4132 fish were obtained from the artisanal hand‐line fishery catch at the Lakbi and Salalah landing sites from April 2005 to March 2007. Size distribution ranged from 16 to 64 cm [total length (TL)]. About 67.5% of the catch was composed of fish measuring <32 cm TL. Neither sex dominated the population nor were there significant differences in the monthly and annual sex‐ratios tested by chi‐squared. Spawning is from May to October. The declining trend in the hepatosomatic indice (HPI) values from September to February was almost identical to the declining trend in the gonado‐somatic indice (GSI) values. The rise and fall in the condition factor (CF) values could not be related to the spawning period. Females and males mature at 31.9 and 33.7 cm TL, respectively. Otolith readings indicated the life span to be about 13 years. The instantaneous rate of natural mortality was estimated with M  = 0.62 year^?1.     

Sex‐specific prey partitioning in breeding piscivorous birds examined via a novel,noninvasive approach

Piscivorous birds frequently display sex‐specific differences in their hunting and feeding behavior, which lead to diverging impacts on prey populations. Cormorants (Phalacrocoracidae), for example, were previously studied to examine dietary differences between the sexes and males were found to consume larger fish in coastal areas during autumn and winter. However, information on prey partitioning during breeding and generally on sex‐specific foraging in inland waters is missing. Here, we assess sex‐specific prey choice of Great Cormorants (Phalacrocorax carbo) during two subsequent breeding seasons in the Central European Alpine foreland, an area characterized by numerous stagnant and flowing waters in close proximity to each other. We developed a unique, noninvasive approach and applied it to regurgitated pellets: molecular cormorant sexing combined with molecular fish identification and fish‐length regression analysis performed on prey hard parts. Altogether, 364 pellets delivered information on both, bird sex, and consumed prey. The sexes differed significantly in their overall prey composition, even though Perca fluviatilis, Rutilus rutilus, and Coregonus spp. represented the main food source for both. Albeit prey composition did not indicate the use of different water bodies by the sexes, male diet was characterized by higher prey diversity within a pellet and the consumption of larger fish. The current findings show that female and male cormorants to some extent target the available prey spectrum at different levels. Finally, the comprehensive and noninvasive approach has great potential for application in studies of other piscivorous bird species.     

Factors affecting estimates of size at age and growth in grey triggerfish Balistes capriscus from the northern Gulf of Mexico

Growth zones in dorsal spines of grey triggerfish Balistes capriscus from the northern Gulf of Mexico were utilized to estimate growth and examine factors that may affect estimates of size at age. Age was estimated from dorsal‐spine sections of 4687 individuals sampled from U.S. waters during 2003–2013, including both fishery‐independent (n = 1312) and fishery‐dependent (n = 3375) samples. Ninety‐six per cent (n = 4498) of these sections were deemed suitable for ageing; average per cent error between two independent readers was 10·8%. Fork length (L_F) ranged from 65 to 697 mm and age estimates from 0 to 14 years. Both sex and sample source (fishery‐independent v. recreational) significantly affected estimated size at age for 2–6 year‐old fish. Data were pooled between sources to fit sex‐specific von Bertalanffy growth functions. Results for the female model were L_∞ = 387 mm L_F, k = 0·52 year^?1 and t₀ = 0·01 year, while for males L_∞ = 405 mm L_F, k = 0·55 year^?1 and t₀ = 0·02 year. These results were significantly different between sexes and indicate clear sexual dimorphism. Thus, growth should be modelled separately by sex when examining population parameters or conducting stock assessment modelling. The positive bias in estimates of size at age computed for recreational v. fishery‐independent samples also has clear implications for stock assessment as growth functions computed with fishery‐dependent samples would tend to overestimate stock productivity.     

Length–weight and length–length relationships and length at first maturity for freshwater fish species of the Salto Santiago Reservoir,Iguaçu River Basin,Brazil

Length‐weight (LWR) and length‐length (LLR) relationships were estimated for 20 species and lengths at first maturity (L₅₀) for six species of freshwater fishes caught in the Salto Santiago Reservoir, Iguaçu River Basin, Brazil. In nine species significant differences were found in the LWR between sexes. Average b‐value for species with no differences between sexes in LWR was 3.12 (SE = ±0.05). Average b‐value in LLR was 0.823. First references on LWRs and L₅₀ are presented for 13 and four fish species, respectively, as well as the new maximum total lengths for eight species.     

Length-weight relationship of three commercially important fish species from Mocka water,southern Red Sea,Yemen

Length-weight relationship was estimated for three fish species, including: Lethrinus microdon (Valenciennes, 1,830), Sphyraena jello (Cuvier, 1829) and Euthynnus affinis (Cantor, 1849). Specimens were sampled between May 2014 and June 2015 from the fish caught by the local artisanal fishery and landed in main fishing landing site of Mocka city. Values of b for fish ranged from 2.644 for S. jello to 2.706 for E. affinis and 3.187 for L. microdon. The determination coefficient (r²) between total length and total body weight ranged from .952 in E. affinis to 0.957 in S. jello and 0.960 in L. microdon.     

Length–weight relationships of five fish species from the Nujiang River (Salween basin), southwest China

This study provides the total length–weight relationships (LWRs) for five fish species collected from the Nujiang River, southwest China. Samples were obtained in May 2015 and May 2016 using drift net and electroshock fishing techniques. A total of 502 specimens belonging to five fish species were analyzed; their LWRs were calculated. The five fish were Schizothorax nukiangensis, Akrokolioplax bicornis, Creteuchiloglanis kamengensis, Channa gachua and Glyptothorax trilineatus. Prior to this study, the length‐weight relationship for S. nukiangensis is unknown to FishBase and new maximum lengths are recorded for A. bicornis and C. kamengensis.These results are useful for fishery research, conservation and management in the Nujiang River.     

Growth and maturation of roker Raja clavata L. in the Solway Firth

Two hundred and seventy-one Raja clavata taken by otter trawl from the Solway Firth were examined for size, sex and state of maturity. Size relationships for both sexes were similar. Total length and disc width were linearly related as were disc width with wing width. Males and females appear to mature at 42 and 45 cm disc width respectively. The Solway population is heavily exploited by an unrestricted commercial fishery and a considerable proportion (48·6%) of the presently retained catch is immature. It is suggested that fishing pressure has brought about a reduction in the size at which female fish mature.     

Length–weight relationships of six tropical fish species from Chilika Lagoon,India

The length weight relationships (LWRs) of six tropical fish species from Chilika Lagoon, India were studied. Specimens were caught using a wide range of fishing gear operated in the lagoon from January to December 2014. The fresh specimens were measured for total length and weight, then dissected and the sex confirmed. Previously unavailable in FishBase, the detailed LWRs of Daysciaena albida, Eleutheronema tetradactylum, Etroplus suratensis and Mystus gulio are reported for the first time. Maximum total lengths reported for Nematalosa nasus and Osteogeneiosus militaris in this study are new records for these species. The existence of a differential growth between male and female O. militaris was confirmed, which was not known earlier.     

Length–weight relationships and length at first maturity for nine fish species of floodplain lakes in Central Amazon (Amazon Basin,Brazil)

Length–weight relationships are presented for nine fish species from the floodplain lakes in the Central Amazon (Amazon Basin, Brazil). The parameter slope b values in the length–weight relationships ranged from 2.33 to 3.28 for grouped sexes, and from 2.7 to 3.61 for separated sexes. Differences between sexes were verified in three species. Sizes at first sexual maturation ranged from 9.14 to 23.97. This study provides a new reference for the length–weight relationships of six species.     

The evolution of gonad expenditure and gonadosomatic index (GSI) in male and female broadcast‐spawning invertebrates

Sedentary broadcast‐spawning marine invertebrates, which release both eggs and sperm into the water for fertilization, are of special interest for sexual selection studies. They provide unique insight into the early stages of the evolutionary succession leading to the often‐intense operation of both pre‐ and post‐mating sexual selection in mobile gonochorists. Since they are sessile or only weakly mobile, adults can interact only to a limited extent with other adults and with their own fertilized offspring. They are consequently subject mainly to selection on gamete production and gamete success, and so high gonad expenditure is expected in both sexes. We review literature on gonadosomatic index (GSI; the proportion of body tissue devoted to gamete production) of gonochoristic broadcast spawners, which we use as a proxy for gonad expenditure. We show that such taxa most often have a high GSI that is approximately equal in both sexes. When GSI is asymmetric, female GSI usually exceeds male GSI, at least in echinoderms (the majority of species recorded). Intriguingly, though, higher male GSI also occurs in some species and appears more common than female‐biased GSI in certain orders of gastropod molluscs. Our limited data also suggest that higher male GSI may be the prevalent pattern in sperm casters (where only males release gametes). We explore how selection might have shaped these patterns using game theoretic models for gonad expenditure that consider possible trade‐offs with (i) somatic maintenance or (ii) growth, while also considering sperm competition, sperm limitation, and polyspermy. Our models of the trade‐off between somatic tissue (which increases survival) and gonad (which increases reproductive success) predict that GSI should be equal for the two sexes when sperm competition is intense, as is probably common in broadcast spawners due to synchronous spawning in aggregations. Higher female GSI occurs under low sperm competition. Sperm limitation appears unlikely to alter these conclusions qualitatively, but can also act as a force to keep male GSI high, and close to that of females. Polyspermy can act to reduce male GSI. Higher male than female GSI is predicted to be less common (as observed in the data), but can occur when ova/ovaries are sufficiently more resource‐intensive to produce than sperm/testes, for which some evidence exists. We also show that sex‐specific trade‐offs between gonads and growth can generate different life‐history strategies for males and females, with males beginning reproduction earlier. This could lead to apparently higher male GSI in empirical studies if immature females are included in calculations of mean GSI. The existence of higher male GSI nonetheless remains somewhat problematic and requires further investigation. When sperm limitation is low, we suggest that the natural logarithm of the male/female GSI ratio may be a suitable index for sperm competition level in broadcast spawners, and that this may also be considered as an index for internally fertilizing taxa.     

Length–weight relationships of six fish species from the Coastal Waters of Jask,Iran

The length–weight relationships (LWRs) for six species were determined, namely Carangoides chrysophrys (Cuvier, 1833), Drepane longimana (Bloch & Schneider, 1801), Euthynnus affinis (Cantor, 1849), Polydactylus plebeius (Broussonet, 1782), Pomadasys kaakan (Cuvier, 1830) and Pseudorhombus elevatus (Ogilby, 1912). Fish was sampled from the Coastal Waters of Jask, Iran (located in Hormozgan Provinces) between October 2011 and March 2012. This work revises previous literature in the Jask and provides the first reference on weight–length parameters for two fish species worldwide and for six species of the Coastal Waters of Jask, Iran.     

Genomic characterization of sex‐identification markers in Sebastes carnatus and Sebastes chrysomelas rockfishes

Fish have evolved a variety of sex‐determining (SD) systems including male heterogamy (XY), female heterogamy (ZW) and environmental SD. Little is known about SD mechanisms of Sebastes rockfishes, a highly speciose genus of importance to evolutionary and conservation biology. Here, we characterize the sex determination system in the sympatrically distributed sister species Sebastes chrysomelas and Sebastes carnatus. To identify sex‐specific genotypic markers, double digest restriction site – associated DNA sequencing (ddRAD‐seq) of genomic DNA from 40 sexed individuals of both species was performed. Loci were filtered for presence in all of the individuals of one sex, absence in the other sex and no heterozygosity. Of the 74 965 loci present in all males, 33 male‐specific loci met the criteria in at least one species and 17 in both. Conversely, no female‐specific loci were detected, together providing evidence of an XY sex determination system in both species. When aligned to a draft reference genome from Sebastes aleutianus, 26 sex‐specific loci were interspersed among 1168 loci that were identical between sexes. The nascent Y chromosome averaged 5% divergence from the X chromosome and mapped to reference Sebastes genome scaffolds totalling 6.9Mbp in length. These scaffolds aligned to a single chromosome in three model fish genomes. Read coverage differences were also detected between sex‐specific and autosomal loci. A PCR‐RFLP assay validated the bioinformatic results and correctly identified sex of five additional individuals of known sex. A sex‐determining gene in other teleosts gonadal soma‐derived factor (gsdf) was present in the model fish chromosomes that spanned our sex‐specific markers.     

Biometric relationships between body and otolith measurements in nine demersal fishes from north‐eastern Tasmanian waters,Australia

Relationships between fish and otolith measurements were analyzed in nine demersal fishes from the north‐eastern Tasmanian waters: Foetorepus calauropomus, Trachurus declivis, Parequula melbournensis, Neosebastes scorpaenoides, Platycephalus aurimaculatus, Platycephalus bassensis, Platycephalus conatus, Lepidotrigla mulhalli and Lepidotrigla vanessa. The values of exponent b from the relationships between fish weight and fish total length, total length and otolith length, total length and otolith width, and fish weight and otolith length were estimated. All above relationships were statistically significant. The analysis of covariance (ANCOVA) was used to test the effect of the categorical factor of species in the fish length and otolith length relationship. Significant differences in fish length and otolith length relationship between species were highlighted in both gurnards and flatheads. Results from this study will provide novel information on quantitative biometric relationships between body and otolith measurements of fish species in Australian waters.     

Morphometric relationships for four Scombridae fish species in Australian waters

Morphometric relationships (length–weight and fork length–total length) were estimated for four scombrid species (Thunnus tonggol, Euthynnus affinis, Cybiosarda elegans, and Rastrelliger kanagurta) that are of growing importance to fisheries, but are also important predators representing different trophic levels in the neritic regime of Australian waters. The sample of 1,137 fish representing a broad size range for each species produced highly significant model fits (r² > .95) that provide researchers with reliable information for future biological studies, stock assessment, and ecosystem models.     

A genetic linkage map of red drum,Sciaenops ocellatus

Second‐generation, sex‐specific genetic linkage maps were generated for the economically important estuarine‐dependent marine fish Sciaenops ocellatus (red drum). The maps were based on F₁ progeny from each of two single‐pair mating families. A total of 237 nuclear‐encoded microsatellite markers were mapped to 25 linkage groups. The female map contained 226 markers, with a total length of 1270.9 centiMorgans (cM) and an average inter‐marker interval of 6.53 cM; the male map contained 201 markers, with a total length of 1122.9 cM and an average inter‐marker interval of 6.03 cM. The overall recombination rate was approximately equal in the two sexes (♀:♂ = 1.03:1). Recombination rates in a number of linkage intervals, however, differed significantly between the same sex in both families and between sexes within families. The former occurred in 2.4% of mapped intervals, while the latter occurred in 51.2% of mapped intervals. Sex‐specific recombination rates varied within chromosomes, with regions of both female‐biased and male‐biased recombination. Original clones from which the microsatellite markers were generated were compared with genome sequence data for the spotted green puffer, Tetraodon nigroviridis; a total of 43 matches were located in 17 of 21 chromosomes of T. nigroviridis, while seven matches were in unknown portions of the T. nigroviridis genome. The map for red drum provides a new, useful tool for aquaculture, population genetics, and comparative genomics of this economically important marine species.     

Length–weight relationships of two schizothoracinae fish species from the Maquan River,the upper reaches of the Yarlung Zangbo River,Tibet, China

Length‐weight relationships (LWRs) were determined for two endemic fish species from the Maquan River, the upper of the Yarlung Zangbo River: (Ptychobarbus dipogon Regan, 1905, Schizothorax waltoni Regan, 1905). All the specimens were collected between May and September of 2014. Length–weight relationships for these two fish species were determined for the first time, and new maximum body weights were recorded for these two species. These results will be useful for fishery research, management and conservation of the Yarlung Zangbo River.     

Mosquito female response to the presence of larvivorous fish does not match threat to larvae

1. Several species with complex life‐history traits such as amphibians and insects with aquatic immature stages and terrestrial adults avoid ovipositing in pools containing larvivorous fish. This avoidance response was assumed to be a general one for most fish species. 2. The generality of ovipositing Culex to the presence of three, widespread larvivorous fish species was tested in a set of field experiments with artificial oviposition pools using caged fish. 3. Larval performance was further examined under actual predation by these three fish species. 4. Results show that ovipositing females responded strongly to the presence of caged mosquitofish, Gambusia affinis, while showing no significant response to the presence of caged green sunfish, Lepomis cyanellus, or the pirate perch, Aphredoderus sayanus. All three fish species consumed similar amounts of larvae. 5. This is the first example of species‐specific response differences to predators during mosquito oviposition habitat selection. These results point to the existence of predator‐released kairomones affecting mosquito behaviour. These kairomones may either be species‐specific or vary in concentration among fish, and probably have an important role in the understanding of mosquito spatial distribution.     

Gonadal development and spawning cycle in the digynic hermaphrodite sharpsnout seabream Diplodus puntazzo (Sparidae) off the Canary Islands, northwest of Africa

Diplodus puntazzo is a species characterized by a rudimentary hermaphroditism, with a low level of protandry. The study found that the overall sex ratio was one male to 2.03 females, diverging significantly from 1 : 1, and that there was a ratio of one male to 0.11 transitional fish. The sex ratio varied with season: during the reproductive period the ratio was 1 : 1.86 (male : female), significantly lower than in the non‐reproductive period in which the sex ratio was approximately 1 : 2.26. Both sexes had similar size distributions; however, females were predominant in all size intervals, especially in the larger ones. No significant difference in mean total length (TL) between females (330 mm), males (319 mm) or transitionals (321 mm) was found. The smallest functional female and male analysed were 159 and 157 mm TL, and the largest were 520 and 510 mm TL, respectively. No significant difference in length at first level of maturity, attained at the second year of life, was found between males (281 mm) and females (292 mm), respectively. A protracted spawning season was identified for the species: from September to February, with a peak in November. GSI values followed the same pattern for males and females, with values of females being similar to those of males; the highest values occurred between September and December, with a maximum in November. Occurrence of transitional fish was significantly higher during the month with highest values of GSI than in the resting period. The study found that vitellogenesis did not begin synchronously for all females, and the simultaneous presence of oocytes in all stages of development indicated an asynchronous mode of ovarian development. The presence of postovulatory, together with tertiary yolk vesicle oocytes, indicated that the species is a multiple spawner.     

Length‐weight relationships of six fishes from intertidal and coastal waters in the northern Persian Gulf

The length–weight relationships (LWRs) for six little‐known fish species collected in the northern Persian Gulf (south of Iran) are presented, namely, Plicofollis dussumieri, Pseudotriacanthus strigilifer, Cynoglossus bilineatus, Cynoglossus arel, Solea elongata, and Pseudorhombus elevates.     

Ecology of Allis Shad Alosa alosa and Twaite Shad Alosa fallax in the Solway Firth, Scotland

The basis of this study were 132 adult Allis Shad and 150 Twaite Shad collected as bycatches from salmon stake nets in Scotland on the north side of the Solway Firth. Most (60%) of the Allis Shad were immature fish 2–3 years of age (mean length 305 mm). Mature males were younger (3–5 years) and smaller (mean length 421 mm) than females (4–6 years and 481 mm mean length). The largest Allis Shad was a female of 515 mm and 2183 g. In contrast, almost all the Twaite Shad were mature, the males younger (3–5 years) and smaller (mean length 341 mm) than the females (4–6 years and 364 mm mean length). The largest Twaite Shad was a female of 400 mm and 1213 g. The food of Allis Shad consisted mainly of small zooplankton with some fish and larger Crustacea. Fine vegetable fragments were common in the stomachs and attributed to filter feeding. The food of Twaite Shad was mainly small fish with some Crustacea. Mature Allis Shad of both sexes with large gonads (maximum female GSI: 20.63) were found throughout the spring and summer but no definite evidence of local spawning was obtained. Mature Twaite Shad of both sexes with large gonads (maximum female GSI: 23.32) were found until early July, thereafter most of the fish were spent. It appears that Twaite Shad spawn locally in June. Some hybrids between the two species were found.