Reproductive biology of the South West Atlantic marbled sand skate Psammobatis bergi Marini, 1932 (Elasmobranchii, Rajidae)

The reproductive biology of Psammobatis bergi was investigated based on 92 males and 136 females skates taken from the coastal bottom trawl fishery at Puerto Quequén, Argentina. The relationship between total body mass and total length (TL) was not significantly different between sexes, but females were heavier than males. Minimum length at maturity in males was 451 mm TL with a length ratio of 74%, whereas females were 415 mm TL with a length ratio of 74%. TL at which 50% of males were mature was 457.6 mm (75.6% of the largest male) and for females was 441.6 mm (79.1% of the largest female). The results indicate a continuous reproductive cycle during the year, with a maximum number of females carrying egg cases in warmer seasons.     

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).     

Reproduction of the sandpaper skate,Bathyraja kincaidii (Garman 1908) in the eastern North Pacific

The sandpaper skate, Bathyraja kincaidii, is commonly taken as bycatch in trawl fisheries off central California. The impact of fisheries exploitation on this population is unknown, however little is known about its biology, including its reproductive life history. To determine reproductive aspects of B. kincaidii, 506 individuals were collected from commercial trawls, museum collections, and monthly trawl and longline surveys conducted by the National Marine Fisheries Service. Males ranged from 112 to 635 mm TL, whereas females ranged from 113 to 610 mm TL. Males reach first maturity at 440 mm TL and at ~3 years, whereas females reach first maturity at 450 mm TL, approximately 1 year later. Size and estimated age at 50 % maturity were similar between sexes: 492 mm TL and 7.5 years for males and 467 mm TL and 7.1 years for females. Gonadosomatic index (GSI) and hepatosomatic index (HSI) values indicate a continuous reproductive cycle, with a seasonal peak in the summer and fall, and a resting period following egg case deposition.     

Validated age and growth of the leopard shark,Triakis semifasciata,with comments on reproduction

Synopsis The age, growth, and sexual maturation of the leopard shark, Triakis semifasciata, from central California were studied. Growth band counts in vertebral centra of 162 leopard sharks produced von Bertalanffy growth curves with L, K. and t_o parameters of 1536 mm. 0.082, and -2.31, respectively, for both sexes combined. The L₈ value for females (1602 mm TL) was slightly but insignificantly higher than for males (1499 mm TL), but the K and t_o values were almost identical. Seasonal changes in size modes of young-of-the-year leopard sharks, centrum edge characteristics, and growth and tetracycline mark-recapture from the field were used to validate annual deposition of vertebral centrum band pairs. Sexual maturity was evaluated by the gonads and presence of sperm and eggs; males mature at 7 yr and at about 63% of asymptotic length, and females mature at 10 yr, and at about 72% of asymptotic length. This slow growth, late maturity, and relatively low fecundity may increase their susceptibility to over-exploitation.     

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 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.     

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 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).     

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.     

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.     

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.     

The multiple spawning pattern of weakfish in the Chesapeake Bay and Middle Atlantic Bight

Weakfish Cynoscion regalis were collected from commercial fisheries in the Chesapeake Bay and the Middle Atlantic Bight (n=4380) during 1989–1992 and their reproductive biology assessed using the gonadosomatic index, macroscopic gonad stages, oocyte diameter distributions, microscopic whole oocyte analysis and histology. Sex ratios were approximately 3:1, females to males, in 1990–1992. Most fish (90%) attained sexual maturity by age 1 and at a small size. Estimated mean length at first maturity was: 164mm total length (TL) for males, and 170 mm TL for females. Weakfish spawn within the Chesapeake Bay, as far north as the Virginia/ Maryland border. Although spawning occurred during May–August and gonad development and initiation of spawning was synchronous, cessation of spawning was asynchronous. There was no indication that older fish exhibited a more extended spawning season than younger fish. Weakfish are multiple spawners with indeterminate fecundity. Oocyte development is asynchronous with oocytes of all stages being present in developed ovaries. Because of the complex and dynamic weakfish ovarian cycle, typical methods of assessing reproduction, such as the GSI and macroscopic gonad stages, are inadequate for this species if not used in conjunction with more detailed methods such as histology.     

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.     

Reproduction and population aspects of the yellownose skate, Dipturus chilensis (Pisces, Elasmobranchii: Rajidae), from southern Chile

The total length (TL) at sexual maturity by sex, fecundity characteristics, and some population aspects (size structures and sexual proportions) are presented for the yellownose skate, Dipturus chilensis , in the eastern South Pacific Ocean. Samples were taken between January 2003 and August 2004 from three zones (principal fishing grounds for the species) in Chile's southern channels (41°30'S–55°10'S). TL at which 50% of the individuals reach maturity was significantly different by sex, with females estimated to mature at 103.9 cm and males at 89.7 cm. The average estimated fecundity was 23.4 (SD 6.4) ova per female. We report on the relationships of clasper lengths and oviducal gland widths with TL and the stages of maturity. Length compositions were statistically different by sex in the same zone (P < 0.05) and between zones for combined sexes (P < 0.05). The proportion of females increased when these reached the TL at which 50% attained maturity, becoming highly available to the fishing gear, possibly in relation to the reproductive strategy. Finally, the results yielded valuable knowledge about population responses to exploitation through fishing.     

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.     

Size at the onset of sexual maturity in the anomuran crab, Aegla uruguayana (Aeglidae)

The size at maturity was studied in the crab Aegla uruguayana from the Areco River (31°14′ S, 59°28′ W), Argentina. Size at sexual maturity was determined according to three criteria: morphometric (change in the relative growth of reproductive characters), histological (first maturation of gonads) and functional (capability to mate and carry eggs). Regarding females, morphometric maturity occurred at a carapace length (CL) of 11.50 mm, considering abdomen width as a reproductive character. Gonad maturity of females could be observed at a minimum size ranging from 15 to 17 mm CL. The smallest ovigerous female observed in the field was 15.60 mm CL, although a relevant population incidence of ovigerous females (86.6%) has just been observed at values higher than 17 mm CL. As for males, the relative growth of the left chela length changed at a value of 15.40 mm CL, while morphological changes in sexual tube occurred between CL of 14 and 16 mm. Testicular maturation occurred at a CL ranging from 17 to 19 mm. The smallest size of males having spermatozoids in their vasa deferentia was 18.70 mm CL. The results obtained indicated that, in both sexes, functional maturity occurred after morphometric maturity and at a size similar to that of gonad maturity. Comparing sexes, females acquired sexual maturity (morphometric, gonad and functional maturity) at sizes statistically smaller than those of males.     

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.     

Growth and life history traits of Aegean chub,Squalius fellowesii (Günther, 1868) in streams in Muğla Province,Aegean coast,Turkey

To aid in species' conservation, the aim of this study was to provide initial findings on age, growth and reproduction of an endemic species, Aegean chub Squalius fellowesii (Günther, 1868) populations from streams in the Aegean region of Mu?la Province, Turkey. The species is relatively short‐lived (maximum 6 years), attaining a size of about 200 mm total length with a rapid growth to first maturity (≈60 mm TL), and relatively little growth thereafter. The male:female ratio was 1.0 : 0.6, males significantly outnumbering females in the majority of the streams. General condition values of individual fish varied between 2.9 and 3.4. Sexual maturity was usually achieved later and at larger sizes in females than in males. Sexual maturation in most populations was at the age of 2 years in females and 1 year in males. The species spawns between early April and late May. Mean absolute and relative fecundity were about 4440 eggs and 57 eggs·g^?1, respectively. Mean egg diameter was 1.00 ± 0.03 mm, ranging from 0.70 to 1.20 mm. Suggestions for the conservation of Aegean chub are discussed.     

Gonadosomatic index‐based size at first sexual maturity of the catfish Eutropiichthys vacha (Hamilton, 1822) in the Ganges River (NW Bangladesh)

This study describes the size at first sexual maturity, length–weight relationships (LWR) in relation to size at first sexual maturity, and Fulton’s condition factor (K_F) of Eutropiichthys vacha in the Ganges River, northwestern Bangladesh. Sampling was done using traditional fishing gear including cast nets, square lift nets and conical traps during January and April, and July to December 2010. For each individual, total length (TL) was measured to the nearest 0.01 cm, and total weight (BW) was determined to the nearest 0.01 g. The gonadosomatic index (GSI) was calculated by the equation, GSI (%) = (Gonad weight in g/BW) × 100. The size at first sexual maturity of males and females was estimated by the relationship between gonadosomatic index and total length. A total of 583 specimens (289 males; 294 females) ranging from 8.30 to 27.00 cm TL and 3.16 to 159.50 g BW were analyzed. Sizes at first sexual maturity for male and female E. vacha were 13.15 and 14.00 cm TL, respectively. The analysis of covariance (ancova ) revealed significant differences in slope and intercept between early and late phases for males (F = 4.532, P < 0.001) and females (F = 21.984, P < 0.001). The K_F was not significantly correlated with TL for males (r_s = 0.052; P = 0.378), but was highly correlated for females (r_s = ?0.165; P = 0.005). This study establishes a strong base for monitoring changes in length at first sexual maturity attributable to high fishing pressures or other reasons within the Ganges and associated river ecosystems.     

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.