Reproductive biology of albacore Thunnus alalunga

Reproductive variables in albacore Thunnus alalunga were evaluated by gonad histology in samples of 132 males (58–118 cm fork length, L_F) and 112 females (59–101 cm L_F) that were collected from the western North Pacific Ocean from 2001 to 2006. In the sex ratio examination, males greatly outnumbered females in large adult fish (L_F > 100 cm). Thunnus alalunga exhibited a protracted spawning period from March to September in the waters off eastern Taiwan and the Philippines, and the peak spawning activity occurred in March and April. Minimum sizes associated with the classification of mature fish were 78 and 83 cm L_F for males and females, respectively. In addition, the largest L_F of immature fish were 93 cm for males and 94 cm for females. The spawning frequency estimate in April was 1·7 days. Batch‐fecundity estimates of 21 females (89–99 cm L_F) ranged between 0·17 and 1·66 million eggs (mean ±s.d . = 0·94 ± 0·43). The relative fecundity estimates of the 21 females ranged between 9·2 and 92·4 oocytes g^?1 body mass (mean ±s.d . = 50·5 ± 22·8). The results presented in this study provide increased information regarding this species' reproductive‐related characteristics than are currently available in stock status determinations.     

Timecourse of oocyte development in saithe Pollachius virens

Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre‐spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October–early November, at a leading cohort size (C_L) of c. 250 µm, after which oocytes grew rapidly in size until spawning started in February. Notably, a distinct cortical alveoli stage was virtually absent with yolk granules observed in developing oocytes at the very beginning of vitellogenesis. Little atresia was observed pre‐spawning, but atretic re‐absorption of remnant oocytes containing yolk granules was found in all females immediately post‐spawning. As expected, concentrations of sex steroids, oestradiol‐17β (females), testosterone (both sexes) and 11‐ketotestosterone (both sexes), increased pre‐spawning before dropping post‐spawning. The present experiment provides the first validation of sex steroid levels in P. virens. Post‐ovulatory follicles were visible in histological sections from female gonads 9–11 months post‐spawning, but then disappeared. Spawning commenced around a C_L of c. 750 µm (700–800 µm). Hydrated oocytes (eggs) measured between 1·04 and 1·31 mm (mean = 1·18 mm) with decreasing sizes towards the end of spawning. The average estimated realized fecundity was c. 0·84 million eggs (median female total length, L_T = 60 cm). Spawning lasted from 13 February to 29 March.     

Life‐history traits of the long‐nosed skate Dipturus oxyrinchus

This work investigates life‐history traits of the long‐nosed skate Dipturus oxyrinchus, which is a common by‐catch in Sardinian waters. The reproductive variables were analysed from 979 specimens sampled during scientific and commercial hauls. Females (10·4–117·5 cm total length, L_T) attained larger sizes than males (14·5–99·5 cm L_T). To evaluate age and growth, a sub‐sample of 130 individuals (76 females and 54 males) were used. The age was estimated by annuli counts of sectioned vertebral centra. Four models were used for the length‐at‐age data: the von Bertalanffy, the exponential, the Gompertz and the logistic functions. According to the Akaike's information criterion, the Gompertz model seemed to provide the best fitting curve (L_∞ mean ± s.e. : 127·55 ± 4·90 cm, k: 0·14 ± 0·09, IP: 3·97 ± 0·90 years). The oldest female and male were aged 17 (115·5 cm L_T) and 15 years (96·0 cm L_T), respectively. Lengths at maturity were 103·5 cm for females and 91·0 cm for males, corresponding to 90% of the maximum observed length in both sexes. The monthly distribution of maturity stages highlighted an extended reproductive cycle, with spawning females and active males being present almost throughout the year, as confirmed by the gonado‐somatic index. Ovarian fecundity reached a maximum of 26 yolked follicles with a mean ± s.e. size of 19·7 ± 6·5 mm.     

Reproductive aspects of the Atlantic angel shark Squatina dumeril in the southern Caribbean Sea

The maturity and reproduction of the Atlantic angel shark Squatina dumeril were assessed using 77 females (29·2–110·4 cm total length; L_T) and 269 males (58·7–108·2 cm L_T) harvested by artisanal gillnetters off Venezuela. The biased sex ratio implied segregation or sex‐specific gear selectivity. Based on the development of the reproductive tract, 50% L_T at sexual maturity (L_T50, mean ± s.e .) for females and males were estimated at 86·14 ± 0·64 and 81·55 ± 0·12 cm, respectively. Uterine fecundity ranged between one and six and with a maximum embryo size of 25·7 cm L_T. Gravid females were observed from August to December, including those close to parturition and while the gestation period was not confirmed, the size of ovarian follicles among some specimens implied protraction. The low fecundity of the species supports close monitoring of catches.     

Reproductive biology of female bigeye tuna Thunnus obesus in the western Pacific Ocean

The reproductive biology of female bigeye tuna Thunnus obesus was assessed by examining 888 fish (ranging from 84·9 to 174·4 cm fork length, L_F) caught by Taiwanese offshore longliners in the western Pacific Ocean from November 1997 to November 1998 and November to December 1999 and 258 gonad samples from these fish. The overall sex ratio of the catch during the sampling differed significantly from 0·5, but males were predominant in sizes >140 cm L_F. Reproductive activity (assessed by histology), a gonado‐somatic index, and the size‐frequency distributions of whole oocytes indicated that spawning occurred throughout the year and the major spawning season appeared to be from February to September. The estimated sizes at 50% maturity (L_F50) of females was 102·85 cm (95% c.i .: 90·79–110·21 cm) and the smallest mature female was 99·7 cm L_F. They are multiple spawners and oocytes develop asynchronously. The proportion of mature (0·63) and reproductively active (0·70) females with ovaries containing postovulatory follicles indicated that they spawn almost daily. Batch fecundity for 15 females with the most advanced oocytes (>730 µm) ranged from 0·84 to 8·56 million eggs (mean ± s.d . = 3·06 ± 2·09). The relationships between batch fecundity (F_B, in millions of eggs) and L_F (cm) and round mass (M_R, kg) were (r² = 0·84) and (r² = 0·80), respectively. The parameters estimated in this study are key information for stock assessments of T. obesus in the western Pacific Ocean and will contribute to the conservation and sustainable yield of this species.     

Reproductive parameters of the Pacific angel shark Squatina californica (Selachii: Squatinidae)

Reproductive characteristics of the Pacific angel shark, Squatina californica, were evaluated from 420 specimens obtained from the artisanal fishery in La Paz Bay, Gulf of California, Mexico. Females (99 cm, 6000 g) were larger than males (95 cm, 5000 g) in terms of both total length (L_T) and body mass (M_T). The overall sex ratio was significantly different from the expected 1:1, suggesting sexual segregation of mature individuals in La Paz Bay. Males had developed reproductive organs and calcified claspers from 72 cm L_T; the median size at maturity (L_T50) was 75·6 cm. In females, only the left ovary was functional and mature ovarian follicles were present from 77 cm L_T; the estimated L_T50 was 77·7 cm. For the 10 gravid females sampled, uterine fecundity was between two and 10 embryos. Mature, non‐gravid females with small and large ovarian follicles appeared simultaneously with gravid females with follicles that did not exceed 1·9 cm diameter.     

Reproductive biology and spatiotemporal patterns of spawning in striped marlin Kajikia audax

This study presents the first histology‐based assessment of the reproductive dynamics of south‐west Pacific striped marlin Kajikia audax. Maturity and reproductive status were assessed from histological sections of ovaries (n = 234) and testes (n = 243) of fish caught in commercial longline and recreational fisheries between 2006 and 2009. Spawning peaked in the Coral Sea during November and December at sea surface temperatures between 24·8 and 28·3° C. Lower jaw fork length (L_LJF) at 50% maturity (L_LJF50), a key variable for stock assessment, was estimated to be 2100 ± 102 mm (mean + s.e .) for females and 1668 ± 18 mm for males. Unlike large pelagic tunas Thunnus spp., the proportion of females increased with length and spawning fish formed multiple large‐scale aggregations within a broad latitudinal band. This study provides a starting point for biological parameters needed for stock assessment and conservation of K. audax and introduces the multiple aggregation spawning concept as a reproductive mechanism to explain genetic heterogeneity observed in some highly migratory species.     

Some observations on the biology of two rarely seen deep‐sea chimaerids,Chimaera carophila and Hydrolagus homonycteris

Chimaera carophila (n = 45) and Hydrolagus homonycteris (n = 11), two deep‐sea chimaerids rarely caught in the waters off New Zealand, were collected from research trawl catches and commercial fishery catches around New Zealand at depths between 400 and 1300 m, between 2014 and 2016. Additional preserved specimens of both species (n = 58) from museum collections were analysed for size, sex and maturity. External assessment of male claspers and a combination of internal assessments of female gonad mass and oviducal gland width, were used to determine maturity. For both species, length at first maturity was 0·70–0·82 of their maximum observed chimaera length (L_C), with females maturing at a larger size. Length at maturity for C. carophila (L_C range: 28·7–103·9 cm) was estimated at 72·5 cm L_C for males (n = 163) and 82·5 L_C for females (n = 58). In H. homonycteris, length at maturity (length range: 78·6–99·8 cm L_C) was estimated at 79·1 cm L_C for males (n = 51) and 80·1 cm L_C for females (n = 17). Ovarian fecundity was up to 31 for C. carophila and sperm storage was confirmed in the oviducal gland of this species. Both species preyed on benthic invertebrates. Some C. carophila and H. homonycteris inhabit depths beyond most current fisheries, but both species appear to be relatively rare and have reproductive parameters characteristic of low productivity, which may make these species vulnerable to population decline if mortality was to increase in the future.     

Fecundity regulation by atresia in turbot Scophthalmus maximus in the Baltic Sea

Down‐regulation of fecundity through oocyte resorption was assessed in Baltic Sea turbot Scophthalmus maximus at three locations in the period from late vitellogenesis in April to spawning during June to July. The mean ± s.d . total length of the sampled fish was 32·7 ± 3·1 cm and mean ± s.d . age was 6·2 ± 1·5 years. Measurements of atresia were performed using the ‘profile method’ with the intensity of atresia adjusted according to the ‘dissector method’ (10·6% adjustment; coefficient of determination was 0·675 between methods). Both prevalence (portion of fish with atresia) and intensity (calculated as the average proportion of atretic cells in fish displaying atresia) of atresia were low in prespawning fish, but high from onset of spawning throughout the spawning period. Atretic oocytes categorized as in early alpha and in late alpha state occurred irrespective of maturity stage from late prespawning individuals up to late spawning fish, showing that oocytes may become atretic throughout the spawning period. Observed prevalence of atresia throughout the spawning period was almost 40% with an intensity of c. 20%. This indicates extensive down‐regulation, i.e. considerably lower realized (number of eggs spawned) v. potential fecundity (number of developing oocytes), suggesting significant variability in reproductive potential. The extent of fecundity regulation in relation to fish condition (Fulton's condition factor) is discussed, suggesting an association between levels of atresia and fish condition.     

Life‐history characteristics of the large Amazonian migratory catfish Brachyplatystoma rousseauxii in the Iquitos region,Peru

The main life‐history traits of the dorado Brachyplatystoma rousseauxii, a large Amazonian catfish undertaking the largest migration known for a freshwater fish species (from the nursery area in the estuary of the Amazon to the breeding zones in the head waters of the western Amazon basin close to the Andes), were determined from a 5 year sampling of >15 000 specimens in the Peruvian Amazon. The breeding season occurred during the falling and low‐water periods, which is hypothesized to be an adaptation to maximize the chances of young stages to reach the estuary. The size at first sexual maturity was slightly larger for females than males, c. 91 and 83 cm standard length (L_S), respectively. Both males and females reproduce for the first time at >3 years old. The fecundity per spawning event ranged from 481 734 to 1 045 284 oocytes for females weighing 25 and 34 kg, respectively. Seasonal variations of body condition were similar among sexes, but differed between immature specimens that had a higher condition during the low‐water period and lower condition during rising waters, and mature individuals that showed the opposite pattern. The growth characteristics were estimated by L_S frequency analysis. For females, the best fitting models gave a mean birth date in August, during the height of the breeding cycle, with the following von Bertalanffy growth function parameters: L_S∞ = 153·3, K = 0·29 and t₀ =– 0·37 years. For males, the best fitting model gave a mean birth date in July, also during the height of the breeding period, with L_S∞ = 142, K = 0·30 and t₀ =– 0·36 years. At a given age, females were systematically larger than males and the size difference increased with age. The largest females sampled (148 cm L_S) was 11 years old and the largest male (134 cm L_S) was 9 years old. The mortality estimates were higher for males total (Z) = 1·34, natural (M) = 0·52 and fishing (F) = 0·82 than for females (Z = 0·98, M = 0·50, F = 0·48). The life‐history patterns of B. rousseauxii are discussed in light of the available knowledge about this species and the understanding of its complex life cycle.     

Population structure and reproductive biology of Schilbe intermedius (Teleostei: Schilbeidae) in the Pendjari River,Benin

This study, the first on fish reproduction in the Pendjari River, investigated aspects of the reproductive biology of Schilbe intermedius. A total of 429 females and 239 males were collected from March 2007 to February 2008. Females were larger than males and the sex ratio was 1:1.8 in favour of females. Size at first maturity was estimated to be 14.9 cm and 16.1 cm for males and females, respectively. Absolute fecundity ranged from 1 006 to 83 980 (22 421 ± 16 083) oocytes, and mean relative fecundity was 201 ± 162 oocytes g^?1 of total body mass. Frequency distributions of oocyte diameter suggested synchronous development, with total spawning. Spawning lasted from June to November, coinciding with peaks in rainfall and flooding. Larger females began spawning about two months before smaller ones.     

Length‐weight relationship and reproductive parameters of Botia dario (Hamilton, 1822) in Assam,India

The length‐weight relationships, spawning season, sex ratio, size at first maturity and fecundity of Botia dario (Hamilton, 1822), also known as the Bengal loach, were analyzed based on 556 specimens collected from the wetlands of Majuli Island, Assam between June 2012 and May 2013. The sex ratio (M : F) was 1 : 0.68, differing significantly (P < 0.05) from a 1 : 1 ratio. Size at first maturity (L_m50) was estimated as 6.8 cm for males and 7.4 cm for females. Analysis of monthly variations in the gonado‐somatic index (GSI), the monthly proportions of macroscopic gonadal maturity, and the ova diameter suggest a prolonged spawning season of B. dario from May to August, with a peak in July for both males and females (GSI = 15.0 in females; 7.0 in males). Absolute fecundity varied from 2523 to 51 377, with a mean of 18 367 ± 1254 oocytes per ovary. A positive correlation was recorded between total fecundity and body weight (r² = 0.678).     

Reproductive biology of Bagrus docmak in the Victoria Nile,Uganda

Aspects of the reproductive biology of Bagrus docmak in the Victoria Nile were investigated between November 2005 and October 2006. Macroscopic and histological analysis of the gonads confirmed it as an asynchronous batch spawner which spawns throughout the year with bimodal spawning peaks coinciding with rainfall seasons. The first spawning peak occurred from March to May, the second from September to November. The sex ratio did not significantly deviate from 1:1. Length at sexual maturity was 33.6 cm and 31.6 cm fork length (FL) for females and males, respectively. Batch fecundity ranged from 1 000 eggs in 34 cm FL fish to 43 000 eggs in 79 cm FL fish, and correlated linearly with FL (r = 0.72) and body weight (r = 0.79). Mean relative batch fecundity was 6 eggs g^?1 (SE 2). These results could guide research into the possibility of artificially inducing the fish to spawn, and its subsequent culture.     

Reproductive biology of the crocodile shark Pseudocarcharias kamoharai

From February 2005 to September 2007, a total of 490 crocodile sharks Pseudocarcharias kamoharai, caught as by‐catch in the swordfish and tuna longline fishery that operates in the tropical western Atlantic Ocean, was studied in regard to their reproductive biology. Maximum observed total lengths (L_T) were 1220 and 1090 mm for females and males respectively, with a high proportion of the catch being composed of mature specimens. Sexual maturity was attained at 760–810 mm L_T for males (L_T50 = 800 mm) and 870–980 mm L_T for females (L_T50 = 916 mm). The size at birth was estimated at 415 mm L_T. Temporal variation in gonad morphology and mass suggests that in this region P. kamoharai, an aplacental viviparous species with oophagy, does not show a well‐defined reproductive seasonality, with mating and parturition occurring possibly over an extended period of the year. Mean ±s.d . fecundity was estimated to be 3·9 (± 0·6) pups per reproductive cycle.     

Length‐weight relationships,condition factor,gonadosomatic index‐based size at first sexual maturity,spawning season and fecundity of Aspidoparia morar (Cyprinidae) in the Jamuna River (Brahmaputra River distributary), northern Bangladesh

The present study describes the length‐weight relationships (LWRs), length‐length relationships (LLRs), Fulton's condition factor (K_F), size at first sexual maturity, spawning season, sex ratio and fecundity of the Morari Aspidoparia morar (Hamilton, 1822) (Cyprinidae). Sampling was done using traditional fishing gear jhaki jal (cast net) from July 2010 to June 2011. Total length (TL), fork length (FL) and standard length (SL) were measured with digital slide calipers. Individual body weight (BW) and gonad weight (GW) were determined to an accuracy of 0.01 g for all specimens. The gonadosomatic index (GSI) was calculated and size at first maturity for males and females estimated using GSI and TL as indicators. Female ≥ size at first maturity was used to determine fecundity. A total of 1200 specimens (males = 552, females = 648) ranging from 4.06–12.84 cm TL and 0.53–16.75 g BW were analyzed. The overall coefficient b for the LWR indicated positive allometric growth (>3.00) in males and isometric growth in females (~ 3.00). ancova (analysis of covariance) revealed significant differences between males and females (P < 0.001). All LLRs were highly correlated (r² > 0.973, P < 0.001). Sizes at first sexual maturity for males and females were 6.0 and 7.0 cm TL, respectively. K_F changed little throughout the year and GSI peaked in November to April, indicating the spawning season (GSImax = 15.0 in females, 2.0 in males). Mature females were dominant during the entire spawning season except in April. Mean total fecundity was 6700 ± 3500, ranging from 1860 to 19680. In addition, relative fecundity ranged from 190 to 1200 (mean 560 ± 235) in the Jamuna River. To ensure sustainable management of this species, the protection of mature individuals during the peak spawning season is highly recommended.     

Life‐history strategies of the rock hind grouper Epinephelus adscensionis at Ascension Island

Epinephelus adscensionis sampled from Ascension Island, South Atlantic Ocean, exhibits distinct life‐history traits, including larger maximum size and size at sexual maturity than previous studies have demonstrated for this species in other locations. Otolith analysis yielded a maximum estimated age of 25 years, with calculated von Bertalanffy growth parameters of: L_∞ = 55·14, K = 0·19, t₀ = ?0·88. Monthly gonad staging and analysis of gonad‐somatic index (I_G) provide evidence for spawning from July to November with an I_G peak in August (austral winter), during which time somatic growth is also suppressed. Observed patterns of sexual development were supportive of protogyny, although further work is needed to confirm this. Mean size at sexual maturity for females was 28·9 cm total length (L_T; 95% C.I. 27·1–30·7 cm) and no females were found >12 years and 48·0 cm L_T, whereas all confirmed males sampled were mature, >35·1 cm L_T with an age range from 3 to 18 years. The modelled size at which 50% of individuals were male was 41·8 cm (95% C.I. 40·4–43·2 cm). As far as is known, this study represents the first comprehensive investigation into the growth and reproduction of E. adscensionis at its type locality of Ascension Island and suggests that the population may be affected less by fisheries than elsewhere in its range. Nevertheless, improved regulation of the recreational fishery and sustained monitoring of abundance, length frequencies and life‐history parameters are needed to inform long‐term management measures, which could include the creation of marine reserves, size or temporal catch limits and stricter export controls.     

On reproduction of longfin thornyhead <Emphasis Type="Italic">Sebastolobus macrochir</Emphasis> (Scorpaeniformes: Sebastidae) in waters off the eastern coast of the Kurils

According to data obtained off the eastern coast of the Northern Kurils in October–December 1998, the body length of spawning females of the longfin thornyhead Sebastolobus macrochir is 26–41 cm (on average, 31.5 ± 0.27). Mass spawning is recorded in females 28 cm in length and longer. The individual absolute fecundity of females is 69355-411710 (on average, 189086 ± 13662) eggs. The reproductive potential of females of the longfin thornyhead is estimated as 189 million eggs. It is supposed that all females participate in spawning.     

Age, growth, and sexual maturity of the yellownose skate Dipturus chilensis in the south‐eastern Pacific

The age and growth parameters of Dipturus chilensis were estimated by counting growth rings from thin sections of vertebral centra from 400 fish (246 females and 154 males), ranging from 23 to 124 cm total length (L_T), and backcalculating fish lengths at previous ages. Marginal increment analysis lent support to the hypothesis of annual deposition of band‐pairs, which formed during the winter months. The oldest female D. chilensis aged in this study was 21 years and 117 cm L_T, whereas the oldest male was 18 years and 93 cm L_T. A 4·7% index of average per cent error (I_APE) suggested that this is a precise method for calculating the age of D. chilensis. Observed L_T were lower than backcalculated L_T, which implies the influence of Lee's phenomenon. The von Bertalanffy growth equations, based on mean length‐at‐age data, were estimated as L_t = 128·3 (1 ? e^{?0·112 (t + 0·514)}) for females and L_t = 107·8 (1 ? e^{?0·134 (t + 0·862)}) for males where t is age (years). Growth was significantly different between sexes: females reached a larger adult size. Ages and lengths at 50% maturity were estimated at 14 years of age and 106 cm L_T for females and 11 years of age and 86 cm L_T for males. At c. 14 years, there was a decline in growth rates in females. The factor most likely responsible for this was sexual maturity, which caused a discontinuity in growth of female fish. These results show that this species is slow‐growing, long‐lived, relatively large and of delayed maturity, characteristics that make it vulnerable to exploitation.     

Gonad maturation and spawning of cobia,Rachycentron canadum (Linnaeus, 1766) off the Dungun coast,Malaysia

The reproductive biology of cobia, Rachycentron canadum, from the coastal waters of Dungun, Malaysia was studied from June 2014 to May 2015. From commercial trawls, a total of 201 samples (combined sexes) were collected (fork lengths [FL] 37.5–124.0 cm; body weights 0.5–20.4 g). The overall sex ratio of females to males was 1:0.9, which was not significantly different (χ² = 2.12, df = 1; p < .05). Estimations of length at 50% maturity (L₅₀) showed that both sexes matured at approximately 75 cm FL; estimated spawning frequency was 6 days. Mean batch fecundity (BF) ranged from 0.55 to 4.32 million eggs. The average number of eggs per gram of ovary was from 2,100 to 5,400 eggs, and relative fecundity 147 eggs/g. There was a weak positive correlation (r² = .48) between BF and female FL as well as BF with an ovary‐free body weight (r² = .56), possibly due to females being in a continuous spawning condition and some possibly half‐spent, based on the histological examination of the female gonads. Despite cobia being asynchronous spawners, the gonadosomatic index in both males and females showed peaks in June, November, and particularly March. Based on histological examination, spawning‐capable males were encountered throughout the study period, whereas spawning‐capable females in the late developing subphase were found mostly in March and April. This is the first study on the reproductive aspects of cobia in Malaysian waters.