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.     

Reproductive biology of Rioraja agassizi from the coastal southwestern Atlantic ecosystem between northern Uruguay (34°S) and northern Argentina (42°S)

A total of 552 individuals of Rioraja agassizi (257 females and 295 males) were collected by bottom-trawl during research cruises. Sexual dimorphism was observed with females are heavier than males for a given total length (TL). Using logistic regression, it was determined that TL at 50% maturity of males was 475 mm TL and of females 520 mm TL. This estimation agrees with the morphological parameters measured. Although not statistically significant, a peak in reproductive activity was observed in males during late spring and summer. The monthly variation in the gonadosomatic index and oviducal gland width, together with the largest diameter of ovarian follicles, suggests that R. agassizi females have a partially defined annual reproductive cycle with two peaks, one from November (spring) to February (summer) and another in July (winter).     

Reproductive biology of the Brazilian guitarfish,Pseudobatos horkelii (Müller & Henle, 1841) from southeastern Brazil,western South Atlantic

This study provides information on the seasonal occurrence, length‐width relationship, sexual development and size at first maturity of the critically endangered Brazilian guitarfish Pseudobatos horkelii in southeastern Brazil. Samples were obtained from September 2007 to August 2009 from commercial fisheries off São Paulo State coast at depths of 10–50 m, with net mesh sizes of 150 mm in the main net and 100 mm in the cod end. A total of 143 specimens (71 males, 72 females) were analyzed. Total length (TL), disc width (DW), sex and reproductive variables were recorded for each individual. Pseudobatos horkelii presents sexual dimorphism in length‐width relationships, with females attaining larger TL and DW. Females also mature at a larger TL, at 81.1% of the maximum TL, while males mature at 67.8% of the maximum TL. No specimens were captured in winter, and only a small sample size was observed in autumn. Males captured in spring and summer presented semen in the seminal vesicle, indicating that this species may reproduce in the warmer months, as already observed for other Rhinobatidae as well as for P. horkelii in southern Brazil.     

Reproductive biology of deep-sea catsharks (Chondrichthyes: Scyliorhinidae) in the eastern North Pacific

Apristurus brunneus, A. kampae, and Parmaturus xaniurus were caught by trawl and longline between Washington and southern California (48°N to 32°N latitude) from June 2001 through October 2004. In females, oviducal gland width increased with TL in all three species but remained within 4 to 6% of TL. Oocyte diameter increased with TL during reproductive development in all species, and continued to increase with size after reproductive maturity was reached. The weight-length relationships differed significantly among species but not between sexes of any species from the eastern North Pacific combined. Using logistic regression, it was determined that total length at 50% maturity (TL₅₀) of A. brunneus males was 514 mm TL and all A. brunneus males were mature at 547 mm TL. Female A. brunneus reached TL₅₀ at 501 mm TL and all female A. brunneus were mature at 581 mm TL. Apristurus kampae males and females reached TL₅₀ at approximately 485 mm TL and 490 mm TL, respectively. Parmaturus xaniurus males reached TL₅₀ at 444 mm TL and females at 501 mm TL. Gravid female A. brunneus were found in all months of the year, but gravid P. xaniurus were found primarily June through September. Adult A. kampae females were found only in July through November and there were gravid females in all these months. Based upon gonadosomatic indices, I _G, these species may mate within a defined period of time (April through June); however, A. brunneus appear to reproduce throughout the year and P. xaniurus reproduce within a defined season (approximately July through September).     

Hermaphroditism in the lantern sharkEtmopterus unicolor (Squalidae,chondrichthyes)

Of the 70 specimens of the lantern shark,Etmopterus unicolor, collected in Suruga Bay and adjacent waters 22.9% were abnormal hermaphrodites, 30.0% normal males, and 47.1% normal females. Fifteen hermaphrodites had female reproductive organs composed of normal ovaries, oviducts, nidamentai glands and uteri as well as claspers. The clasper lengths of these hermaphrodites increased rapidly after the sharks reached 510 mm TL, the length about equal to the size at maturity for normal females. The ovary and uterus of abnormal females became mature at a total length greater than 500 mm, whereas the size at maturity was about 500 mm TL for normal females compared to 460 mm TL for normal males. In one specimen, the left gonad contained both ovarian and testicular tissues, the bulk of which was testicular.     

Reproductive biology of the skate, Rioraja agassizii (Müller and Henle, 1841), off Puerto Quequén, Argentina

A total of 230 specimens of the skate, Rioraja agassizii, was collected from the commercial bottom trawl fishery of Puerto Quequén, Argentina. During the warmer seasons greater proportions of females were sampled. The largest male and female sampled were 629 and 698 mm total length (TL), respectively. Sexual dimorphism was detected in the relationship between weight ( W )−TL and disc width (DW)−TL, in that females were heavier and wider than males. The smallest mature male and female were 485 and 530 mm TL, respectively. TL at 50% maturity (TL_50%) was estimated at 504 and 570 mm for males and females, respectively. Females exhibited heavier livers than males throughout their lifetimes. Seasonal variations in the gonadosomatic (GSI) and hepatosomatic (HSI) indices, and in the width of the left oviducal gland (OG), along with the greater number of pregnant females sampled during spring, suggested that the peak of the egg laying season could be during this season. The egg cases presented a mean length of 69.01 ± 5.53 mm, mean width of 43.40 ± 1.86 mm and mean weight of 17.00 ± 4.59 g. According to these results specimens from Puerto Quequén and southern Brazil appeared to differ in size, the peak of the egg-laying season and in egg dimensions.     

Reproductive biology of the fanray, <Emphasis Type="Italic">Platyrhina sinensis</Emphasis> (Batoidea: Platyrhinidae) in Ariake Bay,Japan

The reproductive biology of the fanray, Platyrhina sinensis, was examined in Ariake Bay, Japan, from May 2002 until December 2006. Females reached sexual maturity at a larger size than males [total length (TL) at 50% sexual maturity: male, 393 mm; female, 421 mm]. The present data support a distinct annual reproductive cycle for P. sinensis. The gonadosomatic index (GSI) for mature males showed a clear seasonal trend, declining from August to November. Histological observations showed that mature sperm in the testes occurred from August to November when monthly GSI declined. Concomitantly, pre-ovulatory ova were observed in females collected from August to November. These data indicate that mating, ovulation and fertilization occurred from August to November. Near-term embryos, neonates and recent post-partum females also occurred from August to November. Additionally, all post-partum females possessed large pre-ovulatory ova. Parturition occurred from August to November followed immediately by mating, ovulation and fertilization. Mature females become pregnant every year, and the gestation period is almost 1 year. Fertilized uterine eggs without macroscopic embryonic development were present throughout the annual reproductive cycle, indicating that P. sinensis utilizes embryonic diapause as its reproductive strategy. Both reproductive tracts of females were functional, and fecundity ranged from 1 to 12 with a mean of 6.0, increasing with TL.     

New data on sexual dimorphism and reproductive biology of Alaska skate <Emphasis Type="Italic">Bathyraja parmifera</Emphasis> from the northwestern Pacific Ocean

New data on sexual dimorphism and features of reproductive biology of Alaska skate Bathyraja parmifera from the western Bering Sea and the northern Sea of Okhotsk are presented. Based on comparative analysis of 11 external morphological characters, the males differ from the females in the length of the disc and snout length (to the eyes, to the mouth, and to the nostrils). In the western Bering Sea, 50% of the females and 50% of the males reach the first sexual maturity at 84.5 cm TL and 85.2–90.2 cm TL, respectively; in the Sea of Okhotsk, 50% of the males reach their first sexual maturity at 80.8–83.8 cm TL (the assessment depends on the features of the method). Among smaller skates (less than 45 cm TL), the males prevail, but the proportion of the females increases in larger size groups; the sex ratio becomes equal in the exemplars 60–80 cm TL, but the males prevail again among the largest fishes (more than 80 cm TL).     

Reproductive biology of the marine catfish,Genidens genidens (Siluriformes,Ariidae), in the Jacarepaguá Lagoon system,Rio de Janeiro,Brazil

Synopsis Genidens genidens was sampled at the Jacarepaguá Lagoon system (23° S, 43° W), Rio de Janeiro State, Brazil, using cast nets and beach seines, to study its reproductive biology. Spawning period extended from October to February, but was more intense from December to January, coinciding with high surface water temperature and low salinity in the area. After spawning, males mouthbrood the eggs for two to three months until development is completed. Mean length at first maturity for females was approximately 180 mm TL, and at 250 mm TL, all females were mature. Batch fecundity was very low, ranging from 7 to 30 eggs for fish with 170 mm TL (37.0 g TW) to 228 mm TL (104.0 g TW), respectively, and was linearly related to fish total length and total weight. Sexual dimorphism starts after sexual maturity, with females having relatively longer pelvic fins than males. Both sexes exhibited very low condition during the spawning season, probably due to changes in feeding activity related to the reproductive cycle. A strong predominance of males during the main spawning/brooding period suggests that females migrate from the area after spawning is completed.Present address: Virginia Institute of Marine Science, School of Marine Science, The College of William and MaryGloucester Point, VA 23062, U.S.A.     

Reproductive biology of the guitarfish <Emphasis Type="Italic">Rhinobatos hynnicephalus</Emphasis> (Batoidea: Rhinobatidae) in Ariake Bay,Japan

Size at sexual maturity, reproductive cycle, and fecundity of the guitarfish, Rhinobatos hynnicephalus, were examined in Ariake Bay, Japan. Females reached sexual maturity at a larger size than males [total length (TL) at 50% sexual maturity: males, 431 mm; females, 476 mm]. Monthly gonadosomatic indices of males decreased abruptly from July to August. Histological examinations confirmed the presence of mature spermatozoa in the testes in July, with semen in seminal vesicles in July and August. Preovulatory ova were observed in females with near-term embryos in August. Parturition occurred in August, immediately followed by mating, ovulation, and fertilization. Gestation period is approximately 1 year. Fertilized uterine eggs without embryonic development were present throughout the annual reproductive cycle. Embryonic development began in June and ended in August, indicating that R. hynnicephalus undergoes embryonic diapause (9 months). Fecundity increased with TL and ranged from 1 to 9 (mean, 4.4) embryos per litter.     

Reproductive biology of the endemic cyprinid fish Hypselobarbus thomassi (Day, 1874) from Kallada River in the Western Ghats,India

The study provides new information on the reproductive biology of Hypselobarbus thomassi (Day, 1874) an endemic cyprinid fish in the Western Ghats–a biodiversity hotspot of India. A total of 384 specimens (males = 244 and females = 140) were collected monthly from April 2009 to March 2011 from Kallada River of Southern part of Western Ghats, India. Monthly sex ratio indicated that males predominated in the fishery, and an overall sex ratio was significantly different from the expected value of 1:1 (male:female = 1:0.57, x² = 28.17, p < .01). Based on the monthly analysis of gonadosomatic index (GSI) and the proportion of mature individuals, the spawning season of H. thomassi occurred between May to October with a peak in June to August. The length at first maturity (L₅₀) recorded was 290 mm TL in males and 330 mm TL in females. The absolute fecundity ranged between 305 (234 mm TL) to 1,089 (414 mm TL) and relative fecundity oscillated between 77.3–220.69 oocytes/g of fish. The fecundity established a linear relationship with total length, body weight and ovary weight. The findings of this study would be very effective to impose sustainable conservation plan for this threatened species in Kallada River and other Western Ghats river systems.     

Length–weight and length–length relationships,gonadosomatic indices and size at first maturity of Eugerres mexicanus (Steindachner, 1863) (Percoidei: Gerreidae) from the Usumacinta River,Mexico

This study examines the length‐weight (L‐W) and length‐length (L‐L) relationships, gonadosomatic indices, and size at sexual maturity for individuals of the endemic Mexican mojarra, Eugerres mexicanus (Steindachner, 1863) from the Usumacinta River Basin, Tabasco, Mexico. From April 2008 to January 2010, 360 specimens were examined, including 151 (41.9%) male, 179 (49.7%) female and 30 unsexed (8.3%) individuals. Overall female:male ratio was 1.2 : 1. Gonadosomatic index (GSI) values indicate increased reproductive activity during February, with significant differences between males (GSI = 2.07) and females (GSI = 5.48). The mean size at first maturity (L₅₀) was 17.3 cm TL for males and 20.5 cm TL for females.     

Reproductive biology of Psammobatis extenta

Psammobatis extenta collected from the commercial bottom trawl fishery operating in Puerto Quequén, Argentina, between 2000 and 2001, had a sex ratio of 1:1 (535 specimens). Both the largest male and female measured 313 mm total length ( L _T). The relationship between total body mass and L _T was significantly different between sexes; mature females weighed more than mature males for a given L _T. The size at which 50% of males were sexually mature was 262 mm L _T (83·6% of the maximum size), whereas 50% of females were mature at 249 mm L _T (80·0% of the maximum size). The gonadosomatic index in mature males and females was slightly higher during summer, but did not show significant variation over the sampling period. The hepatosomatic index of males and females was higher during the autumn and winter and followed a distinct seasonal pattern. Evidence suggested a continuous reproductive cycle during the year, with a maximum number of females carrying egg-cases in summer.     

Studies on the biology of Nile tilapia (Oreochromis niloticus) in Lake Victoria,Kenya: in light of intense fishing pressure

Nile tilapia Oreochromis niloticus is now the most abundant and commercially important tilapiine in Lake Victoria. From the total of 1 512 fish sampled from commercial gill net fisheries during 2014 and 2015, 809 (54%) were males and 672 (44%) were females, giving an overall sex ratio of 1.20 males: 1.00 females. The mean (± SE) length and weight for all fish were 28.7 (±0.1) cm TL and 506.6 (±7.1) g, respectively. The slope b of the length-weight relationship was 2.98, 3.01 3.01, for males, females, and combined sexes, respectively. The relative condition factor was 1.02 for males and 1.04 for females with little variation across the months of sampling. The length at 50% maturity was estimated as 31.0 cm TL for male Nile tilapia and 26.0 cm TL for females. Sixty percent of the fish in the commercial catches surveyed were below 30 cm TL. Comparisons with earlier studies in this system suggest an overall decline in size at maturity over the past 30 years, which may reflect intense fishing pressure.     

Some aspects of the biology and ecology ofKnipowitschia caucasica (Teleostei: Gobiidae) in the Evros Delta (North Aegean Sea)

Some aspects of the biology and ecology of the gobyKnipowitschia caucasica were studied over a period of 13 months in a poly-to euhaline area in the Evros Delta (North Aegean Sea). This fish grows rapidly in the summer and autumn after hatching, matures after its first winter, breeds from the end of April to the end of July, and grows rapidly again in July–September. The older males perish after their second February, whereas some females have a second breeding season at the end of April/beginning of May, shortly before their death. The fish grows to about 40 mm in total length. There is a positive correlation between the total length (TL) and the standard length (SL) or the cleaned body weight (CW). SL increases slower than TL, whereas CW increases slower than TL in immature individuals and faster in males and females. There is no difference between immature individuals, males and females, in the growth rate of SL, TL and CW, TL. The mean monthly values of the condition factor varies from 0.289 to 0.576 in females and from 0.313 to 0.548 in males. The overall sex ratio of females to males is 1: 1.46. Fecundity ranges from 60 to 217 eggs with a mean value of 109.8 and depends upon size, whereas relative fecundity varies between 968 and 2170 with a mean of 1558. The fish feeds predominantly on benthic amphipods and polychaetes.     

Chemical characteristics and lipid fraction quality of sardines (Sardina pilchardus W.): influence of sex and length

An experimental investigation was carried out on sardines (Sardina pilchardus W.) with the aim to evaluate the influence of sex and total length (TL) on total weight (TW) and fillet weight (FW), chemical composition, and lipid fraction quality. Special emphasis was given with respect to the content of polyunsaturated fatty acids (PUFA), which are considered important from a dietary, nutritional, and functional point of view. Sardines were subdivided as a function of TL and sex. Four groups were obtained: (i) males, TL 130–155 mm, (ii) males, TL 155–180 mm, (iii) females, TL 130–155 mm, (iv) females, TL 155–180 mm. Fatty acid composition and chemical analyses were subsequently carried out on the sardine fillets; results showed higher TW and FW in female sardines and higher percentage value of FW/TW ratio in male sardines, indicating a higher incidence of viscera and other non‐edible parts in females than in males. Moreover, total lipids were on average significantly higher (P < 0.05) in longer specimens (TL = 155–180 mm) than in shorter ones (TL = 130–155 mm). Finally, total saturated fatty acids (SFA) and total mono‐unsaturated fatty acids (MUFA) values were found to be significantly higher in females than in males; such values increased significantly (P < 0.01) only for total SFA from shorter to longer sardines. As for total PUFA, both ω6 and ω3 were found to be higher in male than in female sardines and significantly higher (P < 0.001) in larger than in smaller sizes. Total PUFA/total SFA ratio were in all cases close to 1, with higher values in male than in female sardines and in larger than in smaller specimens.     

Sex-ratio,seasonality and long-term variation in maturation and spawning of the brown shrimp <Emphasis Type="Italic">Crangon crangon</Emphasis> (L.) in the German Bight (North Sea)

Aspects of the reproductive and maturation biology of the brown shrimp Crangon crangon (L.) were studied in various subareas of the German Bight (North Sea). The size-specific sex ratio of C. crangon was examined based on length frequency distribution data. The sex ratio for the smallest size groups at which sex was determined was typically around 0.5, indicating an even ratio between males and females. The proportion of females decreased in the 30–45 mm size range. In length classes larger than 50 mm, the proportion of females constantly increases to 100% at around 60 mm total length. We concluded that sex reversal from male to female may not occur in C. crangon. Size at sexual maturity was determined from the proportion of ovigerous females. Size at maturity (L ₅₀) was estimated as 55.4 and 62.0 mm total length for spring and winter data, respectively. The seasonal spawning cycle was studied over the period 1958–2005. Between mid February and late June and for size classes larger than 65 mm ovigerous shrimps exceeded 80% and reached up to 100% of the females in the population. This period can be seen as the core spawning season. From early August to early December the proportion of ovigerous shrimps in the female population is very low. Interannual differences in the seasonal process are obvious with a dramatic decline in C. crangon reproductive success in the late 1980s. Various options are discussed for the reasons of the decline and recovery of the reproductive performance.     

Reproductive strategy of Labeo senegalensis Valenciennes 1842 (Teleostei: Cyprinidae) in the Ouémé basin,Benin

Aspects of the reproductive biology and population structure of Labeo senegalensis were investigated in the Ouémé River between April 2005 and March 2006. Reproductive strategy was investigated using gonadosomatic index, ovarian structure and fecundity. Average size-at-first-maturity (L ₅₀) was estimated at 29 cm TL for females and 25.7 cm TL for males. The average sex ratio (1:0.96) was not significantly different from unity. Oocyte diameter frequency distribution suggests synchronous development with a single total spawning. Absolute fecundity ranged between 12 948 and 74 832 eggs. Labeo senegalensisis a highly fecund fish that presents a seasonal cycle of reproduction from May to October during the rainy season.     

Reproductive biology of Raja clavata (Elasmobranchii: Rajidae) from Southern Black Sea coast around Turkey

Specimens of Raja clavata were monthly collected at the coast of Havaalan? (Trabzon/Turkey) from January 2009 to December 2009 at depths between 20 and 40?m. A total of 230 individuals of thornback ray (131 females and 99 males) were collected by bottom trawls during research cruises. Using logistic regression, it was determined that TL at 50% maturity of males was 718?mm TL and of females 746?mm TL. The ovarian fecundity ranged from 27 to 60 yellow follicles in both ovaries. Females carrying egg cases were found in July and October. Variations in the gonadosomatic and hepatosomatic indices indicated a continuous reproductive cycle during the year.     

Aspects of reproduction and their implications for the conservation of the endangered limpet,Patella ferruginea

Summary

The protandric limpet, Patella ferruginea G., is the most endangered marine species in the Western Mediterranean and is at serious risk of extinction. Nevertheless, its biology and ecology are little known. In the present work, several reproductive aspects are studied. Recruitment take place in June and the largest individuals are the most scarce. The sex ratio is slanted towards the largest sizes, and the species seems to show sex change at sizes from 60 mm upwards, although males can be observed up to 80 mm. There is no correlation between size of oocytes and shell length; however, the larger females contribute greatly to the reproductive event, with high fecundity and GSI values. The mean diameter of oocytes was observed to be 149.78 μm, whereas the heads of spermatozoa were 3.78 μm long. The results of the present study increase the maximum length for males by double that cited in previous literature and highlight the importance of strictly protecting females (i.e., most of the largest individuals, >60 mm), since their population percentage is very low, in order to develop adequate strategies to preserve the species.