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.     

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.     

Reproduction of Joturus pichardi and Agonostomus monticola (Mugiliformes: Mugilidae) in rivers of the Sierra Nevada de Santa Marta, Colombia

The freshwater mugilids Joturus pichardi and Agonostomus monticola, have been documented on ecological and distribution aspects, mainly for Central American populations, nevertheless, little information is available on their reproductive aspects, specifically in Colombian freshwater environments. Reproductive biology of the mugilids J. pichardi and A. monticola from Sierra Nevada de Santa Marta (SNSM) rivers was studied between July 2005 and December 2006. A total of 14 specimens of J. pichardi and 320 of A. monticola were collected. The reproductive biology was analyzed by means of: sexual proportion, gonadosomatic index, and mean size at maturity, fecundity and oocyte diameter. Additionally, a bioassay was carried out to evaluate the effect of salinity on spermatic motility and its possible relationship with the species' spawning area. These mugilids share habitats with similar ecological characteristics, in which strong currents; clear water and stony areas stand out. Gonadal maturity indicators and indirect evidence are presented to support the relationship between reproductive maturity and higher rainfall levels in the area (September, October and November), as well as the catadromous migration of J. pichardi and A. monticola. This last species females outnumbered males with a sex ratio of 2.3:1. Females mean size at maturity was 172mm of their total length (TL) and 108mm TL for males. Fecundity (F) was 23 925 +/- 4 581 eggs per gram of gonad, and was related to size by the equation F = 395.1TL(1.281); besides, the mean oocyte diameter was 362 +/- 40 microm. Considering the salinity effect on sperm motility in both species, results suggested that J. pichardi spawned in estuarine environments but the species did not migrate to fully marine environments; however, A. monticola withstood a broad range of salinity, suggesting a spawning from intermediate to total saline environments. Both species have high culturing potentials, considering that their feeding is based on plant and macroinvertebrates, their meat quality and the size they are able to reach. These species represent an interesting resource to the fisher groups of the region and should be integrally assessed.     

Size at first sexual maturity of two species of rajoid skates, genera Atlantoraja and Dipturus (Pisces, Elasmobranchii, Rajidae), from the south-western Atlantic Ocean

Total length (TL) at first sexual maturity was estimated for Atlantoraja castelnaui and Dipturus chilensis from the south‐western Atlantic Ocean. Total length at which 50% of the females were captured (50% c) was less than the TL at first sexual maturity (ML) in both species. Immature females are being captured and thus will not become sexually mature to reproduce because of early fishing mortality. Females of A. castelnaui and D. chilensis reach sexual maturity at TLs of 110–114 cm and 102–106 cm, respectively. Males mature with TL between 91 and 95 cm for A. castelnaui and between 83 and 87 cm for D. chilensis.     

Life history notes of the critically endangered dwarf sawfish, <Emphasis Type="Italic">Pristis clavata</Emphasis>, Garman 1906 from the Kimberley region of Western Australia

The dwarf sawfish, Pristis clavata, was captured in marine waters of King Sound and estuarine waters of the Fitzroy, May and Robinson Rivers, in the Kimberley region of Western Australia. Observations of sexual maturity and annuli present on vertebrae suggest that the estuarine waters of at least the Fitzroy River act as a nursery for the species, where immature individuals may remain for at least 3 years. The capture of immature individuals in excess of 2,330 mm TL during the current study in addition to Peverell’s (Peverell in Environ Biol Fishes 73:391–402, 2005) record of a mature male measuring 3,060 mm TL implies that the species may attain far greater lengths than previously reported and that the common name may not be entirely appropriate. In contrast to the sympatric freshwater sawfish Pristis microdon, the number of rostral teeth of individual P. clavata can not be used to differentiate males from females, with both sexes possessing an average of 42 rostral teeth.     

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.     

The biology of the finetooth shark,Carcharhinus isodon

Synopsis The finetooth shark inhabits shallow coastal waters of the western Atlantic from North Carolina to Brazil. It is common off the southeastern United States, where it spends the summer off Georgia and the Carolinas and winters off Florida. The species appears in the nursery and mating areas of South Carolina when the surface water temperature rises above 20° C in late April and early May. Both adults and juveniles are common in the shallow coastal waters of South Carolina through the summer, where they feed primarily on menhaden. The finetooth shark leaves the Carolinas in early fall and migrates southward as the surface water temperature decreases below 20° C. Females reach maturity at about 1350 mm TL. Males mature at about 1300 mm TL. The finetooth shark has consecutive, year-long ovarian and gestation cycles, like most carcharhinid sharks. Mating occurs from early May to early June. Freshly mated females bear a large spermozeugma at the base of each uterus. The spermozeugmata are large almond shaped masses of individual spermatozoa embedded in a supporting matrix. Embryos are lecithotrophic during their first fifteen weeks of development. Subsequently, the embryos establish a placental connection to the mother. Implantation occurs when the embryos measure about 130 mm or at about the fifteenth week of gestation. Gravid females carrying young 480–550 mm TL enter the shallow water nurseries off South Carolina in late May. Parturition occurs from late May to mid-June, after a gestation period of about twelve months, plus or minus two weeks. The young measure 480–580 mm TL at birth. Oocytes grow little during the gestation cycle. After parturition, a cohort of oocytes begins to develop, that will be ovulated the following May. Thus, the ovarian cycle lasts about a year, although most of the oocyte growth occurs in the months just prior to ovulation.     

Changes in size composition of the catches of toothfish Dissostichus eleginoides as a result of longterm long-line fishing in the region of South Georgia and Shag Rocks

The changes in the size composition of the toothfish Dissostichus eleginoides from the long-line catches in division 48.3 (South Georgia and Shag Rocks) and determination of the length at which the males and females mature are investigated, as is the ratio between the mature and immature individuals of this species after the longterm effect of fishing. It was shown that toothfish males reach maturity at smaller lengths than females. Fifty percent of males reach maturity at length of 66–78 cm, while females mature at lengths of 78–96 cm. The ogive of toothfish maturation and its comparison with size and sexual composition of the catches in the first and last years of long-line fishing demonstrated that a significant part of immature and first maturating fishes less than 90 cm in length are removed as the result of fishing at the present time. The decrease in the average size of toothfish in the catches, the high percent of immature fishes in the catches, and the decrease of the portion of large fishes suggest a decrease in its abundance.     

Heteronarce rierai,a new narkid ray from Mozambique,western Indian ocean

Heteronarce rierai sp. nov. is described on the basis of six specimens, one male and five females, caught in the waters off Mozambique (western Indian Ocean). Total lengths range from 257 to 296 mm. The new species is distinguished from the three other species of the genusHeteronarce by its narrower disc width (29.6% of TL in male, and 33.0 to 39.2% of TL in females), shorter disc length (32.7% of TL in male, and 34.4 to 40.6% of TL in females), and its longer interdorsal distance (10.1 to 11.7% of TL).     

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.     

Distribution and ecology of <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis> (Channichthyidae) around South Georgia and Shag Rocks (Southern Ocean)

Chaenocephalus aceratus (Family Channicthyidae) is one of the dominant species of demersal fish living on the South Georgia shelf where it is caught in low numbers as by-catch in the mackerel icefish and Antarctic krill commercial fisheries. Data collected during 14 demersal fish surveys, from 1986 to 2006, are analysed to investigate biomass, distribution, growth and diet. Biomass estimates from a swept area method ranged from 4,462 to 28,740 tonnes on the South Georgia and Shag Rock shelves although few fish were caught at Shag Rocks. Analysis of length frequency data indicated that growth was fast in the first five years with males and females attaining lengths at first spawning of 440 mm TL and 520 mm TL. The diet was comprised of fish and crustaceans, with an ontogenetic shift in diet from Euphausia superba and mysids to benthic fish and decapods observed to begin at 250 mm TL. In larger fish (>500 mm TL) the diet was dominated by fish. C. aceratus diet is sufficiently different from the other species of channichthyids around South Georgia to suggest that these species have undergone resource partitioning.     

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 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.     

Age,growth, maturity and mortality of the tapetail anchovy Coilia brachygnathus (Engraulidae) in Lake Honghu,China

The tapertail anchovy Coilia brachygnathus, a commercially important species mainly distributed along the mid-lower Chang-Jiang basin, is by far the most dominant species in Lake Honghu. To figure out its success in this semiclosed lake, some basic biological parameters of this anchovy were analysed based on samples seasonally collected from October 2020 to December 2021. The results demonstrated that the age classes of fished individuals varied from 0.5 to 3.5, with the majority (97.36%) being between 0.5 and 3 years old. The size at 50% maturity of 17.2 cm total length (TL) for females and 19.0 cm TL for males corresponded to 1 and 1.6 years, respectively. Coilia brachygnathus has a short life span, early sexual maturity and a relatively fast growth rate. The flourishing of the fish in the lake is mainly attributed to its short life span, early maturity, fast growth rate, closed fishing, pelagic spawners, the availability of plenty of food and low predation effect on it. Age 3.5 year occurs in an extremely small percentage of the total (<3%), indicating that a large number of larger-sized or older fish died after spawning, which is probably one of the major sources of water pollution if the closed fishing measure is adopted in Lake Honghu. Thus, individuals older than 2 years or more than 20.0 cm TL should be harvested. These findings have important management implications for the fish resources in Lake Honghu and beyond.     

Reproductive biology of two sympatric skates in the south‐west Atlantic: Psammobatis rudis and Psammobatis normani

The total lengths ( L _T) at which 50% were mature of Psammobatis rudis and Psammobatis normani , in the south‐west Atlantic were: P. rudis , 428 mm for males and 414 mm for females and P. normani , 443 mm for males and 403 mm for females. Clasper length in mature males was greater in P. normani than in P. rudis , whereas oviducal gland width was not different between species. Females of P. normani with egg cases were found in every month sampled, and in January, March, April and July in P. rudis , although insufficient samples were available to identify peak oviposition times. Geographic variation in size frequency and maturity were found. The effects of oceanographic conditions and fishing pressure are discussed. Size at 50% maturity in both species was >74% of the maximum L _T, indicating late sexual maturity and low potential stock recovery rate.     

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 observations on the ecology of Galeus piperatus Springer and Wagner,a little known shark endemic to the Northern Gulf of California*

Galeus piperatus Springer & Wagner, the peppered shark, is a dwarf shark found in the Gulf of California north of the City of Guaymas, Sonora. It has been taken in June and August 1971 and in February and March 1972, and is found from 130–550 m with maximum abundances from 170–420 m deep. Numbers are higher in June and August (up to 110 individuals/ha) than in February and March. In June and August 1971 the area of distribution included all the waters north of Isla Tiburón and Isla Angel de la Guarda, and below the 130 m isobath. During these months Galeus piperatus was found at 12 and 33 stations respectively, but was taken at only one station in the same area during February and March 1972. The fishing effort expended during these periods was 16, 42 and 60 units respectively. It seems likely that a strong migratory movement causes these differences in abundance and distribution. Galeus piperatus has been taken from 50–100 m off the bottom in mid-water trawls at night and is clearly a mid-water and demersal form. Sexually mature females carrying olive green egg cases were taken in large numbers in June 1971 and were also present in reduced numbers in August 1971. Only females 18 cm or more in total length carried egg cases. The migration of Galeus piperatus into the North Gulf of California appears to coincide with sexual maturity.     

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,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.