Reproduction and recruitment of the brown shrimp Crangon crangon in the inner German Bight (North Sea): An interannual study and critical reappraisal

The brown shrimp, Crangon crangon, is the most important target of the coastal crustacean fisheries in the German Bight. In order to evaluate the relation between the abundance of ovigerous females and larvae in spring and the recruitment success in autumn, we first analysed the seasonal appearance of ovigerous females and larvae from weekly samples throughout 2012. The spawning season in the German Bight extends over several months comprising multiple unsynchronized spawning events. The minimum shares of ovigerous females appeared in early autumn, and the highest shares in late winter bearing mostly early egg stages. We defined the putative start of the reproductive cycle for November when the frequency of ovigerous females started to increase. There was no distinct separation between winter and summer eggs, but a continuous transition between large eggs spawned in winter (the early spawning season) and batches of smaller eggs in spring and summer. Larval densities peaked in April/May. Consequently, regular annual larval surveys from 2013 to 2016 were scheduled for April/May and extended to six transects covering the inner German Bight. Ovigerous females were most abundant in shallow waters above the 20‐m isobaths, which also explained regional differences in abundance between the regions off North Frisia and East Frisia. No relation was obvious between the number of larvae in spring and recruited stock in autumn. Due to the short lifespan of C. crangon, the combination of various abiotic factors and predator presence seems to be the principal parameters controlling stock size.     

Reproductive cycle of the venerid clam <Emphasis Type="Italic">Meretrix lusoria</Emphasis> in Ariake Sound and Tokyo Bay,Japan

We assessed the reproductive cycle of the venerid clam Meretrix lusoria by histological analysis of the gonads. Individuals for study were collected from natural populations on the Shirakawa tidal flat, Ariake Sound, and from populations that had been transplanted from the Shirakawa flat to the Oi flat in Tokyo Bay. In both study areas, the reproductive cycle was synchronized between sexes. Gonads of the clam started to develop in early spring and matured during the summer. Mass spawning occurred in the late summer/early fall. The clam matured at a shell length of 17–20 mm, which is much smaller than previously considered. While trophic conditions and salinity differed considerably in the two study areas, water temperatures showed similar seasonal changes (12°C during the winter and around 30°C during the summer). Thus, temperature probably controlled gonadal development. The coincidence of the period of spawning with the period of frequent intrusion of hypoxic waters into the tidal flats in Tokyo Bay suggests that such hypoxic events interfere with clam recruitment and are at least partly responsible for the disappearance of the natural population at this location.     

Reproductive cycle of yellow sea bream <Emphasis Type="Italic">Dentex tumifrons</Emphasis> in Wakasa Bay,the Sea of Japan off central Honshu

ABSTRACT:   To determine the spawning season and reproductive cycle of the yellow sea bream, Dentex tumifrons , in Wakasa Bay, in the Sea of Japan off central Honshu, seasonal change in the gonadosomatic index ( GSI ) was examined and histological observations of both ovaries and testes were conducted. The female GSI gradually increased from May, maintained a high level between August and October and then rapidly decreased. The histological observations of the ovary showed that vitellogenesis began from May and developed until September. Spent fish began to be observed in October and all the fish collected in December were spent. There was only one peak in the seasonal change in GSI of males and females in Wakasa Bay. Thus, yellow sea bream spawn only in autumn in Wakasa Bay. Differences in the reproductive cycle and number of spawning seasons were found between the two different latitudinal areas, Wakasa Bay and the East China Sea (low latitudinal area) where the spawning seasons were spring and autumn. An increase in water temperature is an important factor to initiate gonadal maturation (recrudescence) and is terminated by the short day-length in Wakasa Bay.     

Prediction of timing of mating and egg extrusion in the coconut crab <Emphasis Type="Italic">Birgus latro</Emphasis> judged from female pleonal expansion

A temporal pattern of reproductive activities of biological resources is essential information for the implementation of specific seasonal closures. First we investigated the relationship between the female pleonal expansion and female reproductive condition (i.e., non-ovigerous, ovigerous, or with spermatophores) to clarify the morphological characteristics of female coconut crabs that were able to mate. Second, we mated females with males in captivity to examine the relationship between the degree of female pleonal expansion and mating success. The index of pleonal expansion (ratio of inter-tergite distances to thoracic length) was significantly different among female reproductive conditions; females with spermatophores just before egg extrusion had the most expanded pleon. In the mating trials, all females showing index values higher than 0.35 mated with males. These results indicate that the female pleonal expansion has a strong relation to reproductive activities of females and can be applied as a morphological criterion for selecting females being able to mate. Next, we investigated whether reproductive activities of female coconut crabs are related to the lunar cycle. The reproductive activities were synchronized with the lunar cycle, and most females mated and extruded eggs around the new moon phase. These results have considerable implications for resource management and aquaculture for this species.     

Comparison of spatiotemporal patterns in reproduction of the kuruma prawn Marsupenaeus japonicus between two regions having different geographic conditions in Kyushu, southern Japan

ABSTRACT:   The Yatsushiro Sea and Shibushi Bay are, respectively, located on the western and south-eastern coast of Kyushu, southern Japan. The Yatsushiro Sea is a shallow semi-enclosed inland sea, whereas Shibushi Bay is an open-type bay with a deep and wide mouth facing the open sea. The size at sexual maturity and spatiotemporal patterns of reproduction of the kuruma prawn Marsupenaeus japonicus (Decapoda, Penaeidae) were examined and compared between these two regions. In the Yatsushiro Sea, the size at sexual maturity was estimated to be 131 mm body length. However, the estimated size at sexual maturity was considerably larger (154 mm) in Shibushi Bay. The spawning season of M. japonicus was estimated to continue from April to September in the Yatsushiro Sea, whereas it was estimated to be longer in Shibushi Bay, from March to November. It is believed that the warm water temperature due to the strong effect of the Kuroshio Current prolonged the spawning season of M. japonicus in Shibushi Bay. The spawning grounds were estimated to be in areas deeper than 10 m in the Yatsushiro Sea and deeper than 20 m in Shibushi Bay. In Shibushi Bay, body size distribution of mature females was considered to be less affected by water depth in comparison with the Yatsushiro Sea, although older mature females larger than 200 mm body length also spawned outside of the bay.     

Two spawning stocks of icefish <Emphasis Type="Italic">Neosalanx taihuensis</Emphasis> revealed from annual reproductive cycle analyses

Neosalanx taihuensis were sampled from the Tian-e-zhou Oxbow from March 2006 through November 2007. Two separate spawning seasons were identified based on the annual reproductive cycles of the females, designated as the autumn-spawning season and the spring-spawning season. Lifespan of the offspring of the spring-spawning fish was 1 year, with them dying after the subsequent spring spawning. Autumn-spawned females seem to be the offspring of the spring-spawning fish, based on monthly changes in the length–frequency distributions. Spring-mature females had higher absolute fecundity, gonadosomatic index, and relative condition factor in 2007 than in 2006. Relative condition factor of the immature female offspring of spring-spawning fish was higher in 2007 than in 2006, portending a further increase in reproductive investment during the spring spawning of 2008. The increasing reproductive investment suggests that the population of N. taihuensis in the Tian-e-zhou Oxbow may be recovering from its recent decline.     

Reproductive Performance of Different Sized Wild and Pond-reared Penaeus paulensis Females

The present study analyzes the reproductive performance of three size classes of wild (average weight of 46.5, 55.0, and 63.2 g) and three size classes of pond-reared (18.4, 21.3, and 25.1 g) Penaeus paulensis females. Unilaterally eyestalk ablated females were placed for 70 d in 3.6 m diameter tanks at 6 individuals/m² and a 1.2:1 female-male ratio. Number of spawns, eggs, nauplii, fertilization and hatching rates were recorded every second day. The length of unfed protozoea I larvae was also recorded. Larger broodstock shrimp tended to suffer higher mortality rates. Smaller, pond-reared females started spawning at 28.2 ± 4.1 g. The number of eggs and nauplii per spawning event were not significantly different between experimental groups (P > 0.05), but due to their higher spawning frequency, small wild females (46.5 ± 3.7 g) outperformed medium (55.0 ± 1.8 g) and large ones (63.2 ± 7.0 g). No relationship between protozoea length and spawner size was found. Optimum size for the maturation of wild P. paulensis females was estimated to be from 30 to 60 g. It is suggested that the use of this size range can potentially enhance nauplii production of P. paulensis .     

Annually twice induced spawnings provide multiple benefits: Experimental evidence from an Indian major carp (Catla catla,Hamilton 1822)

Multiple spawnings are special reproductive tactics that many fish evolved to obtain different types of direct and/or indirect spawning benefits. This has led to two pertinent questions: (a) what types of benefit does a commercially important fish provide during multiple induced spawnings annually? and (b) is there any trade‐off between traits during these spawnings? To address these questions, the present study was carried out with two separate experiments during two spawning events of an Indian major carp (Catla catla) to assess: (a) male's spawning performances and (b) female's spawning performances. The male's spawning data revealed that they produced significantly higher amount of milt and hatchlings during the first spawning, while they significantly reduced hatchling deformation rate, enhanced offspring survival rate and enlarged offspring body size during the second spawning. The female's spawning information unveiled no significant differences in total egg weight, hatching rate and hatchling deformation rate between the first and second spawning. However, females had significantly higher offspring survival rate during the first spawning and enhanced offspring body size during the second spawning. Interestingly, the analysis of trait associations revealed that males allocated energy with a trade‐off between milt weight and offspring survival rate, whereas females showed a trade‐off between hatching rate and offspring survival rate. Thus, the study provides some important information for carp breeders and associated stakeholders to know which spawning season is preferable for the higher production of eggs, milt and good quality larvae.     

Reproductive cycle,age, and body size at maturity and fecundity of female willowy flounder <Emphasis Type="Italic">Tanakius kitaharai</Emphasis>

Annual reproductive cycle, age and body size at maturity, and potential and relative fecundity were examined in female willowy flounder in the North Pacific off Japan. Vitellogenesis became active from September, followed by the beginning of spawning in December. The spawning season continued until May with its peak in January. Estimated maturation rate was 50% at a standard length of 16 cm, 30% in 2-year-olds, and almost 100% in ≥3-year-old fish. Potential fecundity increased with age, while relative fecundity decreased in older fish. The results clarify some aspects of the detailed reproductive biology of female willowy flounder and emphasize the importance of age-composition data in estimating reproductive potential within a population.     

Genetic parameters and correlated responses in female reproductive traits in the GIFT strain

The effect of selection for greater growth rate in the GIFT strain on traits related to female reproduction (weight at spawning, number of eggs, number of fry, total weight of fry and number of dead fry) was studied. Available records comprised 10 generations of data from a total of 935 breeding females with known pedigree. Female body weight at spawning was 255 g, whereas the averages for number of eggs, number of live fry at hatching, number of dead fry and total fry weight per spawning were 1444, 908, 64.90, and 7.24 g respectively. Heritabilities for reproductive traits were low to moderate (0.20 for number of eggs, 0.16 for number of hatched fry and 0.11 for fry weight per female at spawning). The genetic correlations between female body weight at spawning and reproductive traits were very low to low (0.01 to 0.31) and not significantly different from zero. The genetic correlations among reproductive traits (i.e. number of eggs, number of hatched fry and fry weight) were high (0.75 to 0.92). Phenotypic correlations were consistent with the genetic correlations, ranging from 0.56 to 0.85. Correlated responses in reproductive traits measured as differences in least squares means between Selection and Control lines were positive and significant (except for the number of dead fry) when age of females at spawning was fitted as a covariate. However, there were no significant differences in all studied traits when body weight of the female at spawning was fitted as a covariate within lines. This indicates that the greater reproductive rate was due to the greater size of females in the Selection line, but the efficiency of reproduction per unit weight of female did not change as a consequence of selection for growth.     

Reproductive season and female maturity size of coconut crab <Emphasis Type="Italic">Birgus latro</Emphasis> on Hatoma Island,southern Japan

Information about reproductive season, size at sexual maturity and size-dependent reproductive potentials is important for efficient resource management. Such information is necessary to determine seasonal closures and minimum legal size limits. To conserve resources of coconut crab Birgus latro, which are in danger of extinction due to excessive exploitation, their reproductive season, female size at functional maturity and relationship between female size and reproductive potentials were investigated. The reproductive season started in early June and ended late August, and females with higher reproductive potentials showed a tendency to spawn early in the reproductive season. The prohibition of exploiting the resources during the reproductive season, especially early in the season, would be appropriate for sustainability of high reproductive outputs. Fifty percent of investigated females matured functionally at 24.5-mm thoracic length (TL). However, the size at which all females reached functional maturity was 32.3 mm TL, and there was a wide variation in the size of functional maturity among individuals. We must determine minimum legal size by taking the variation into account to allow all individuals to mate at least once before they are caught, which may prevent serious depression in reproductive rate and genetic diversity.     

Natural spawning,embryonic and larval development of F2 hybrid grouper,tiger grouper Epinephelus fuscoguttatus × giant grouper E. lanceolatus

This study aims to reveal the first report of the natural spawning of F1 hybrid grouper (TGGG), a crossbreed between the tiger grouper, Epinephelus fuscoguttatus × giant grouper, E. lanceolatus, since its first production in 2006. This marks the completion of its full cycle after a 10-year period. In order to establish a seed rearing protocol for a novel F2 hybrid TGGG, natural spawning, embryonic and larval developments were thoroughly observed. Five batches of natural spawning were recorded with an average of 1.50–15.3 kg eggs collected, while fertilization and hatching rates were recorded at 85.3–97.6%, and 63.0–98.3%, respectively. F2 larvae hatched out at 17:50 hours with an average body size of 1.74 ± 0.01 mm, and a yolk sac volume of 0.85 ± 0.197 mm3. The first feeding was initiated 3 days after hatching, which coincided with the onset of functional feeding apparatus and active swimming behavior. Larval dorsal and pelvic spines were formed at 6 days AH coupled with dynamic feeding activity, as more food was found in the digestive tract. Meanwhile, the F2 hybrid grouper shifted habitat from pelagic to benthic as early as 25 days AH, and entered a juvenile stage at 35 days AH, attaining a skin coloration similar to that of the F1 juvenile. This study concluded that naturally spawned eggs of F2 hybrid TGGG were exceptionally high in quality, although larvae were small and fragile, and performed vigorous feeding activities and cannibalistic behavior. Thus, these findings can serve as primary data to further develop the optimal rearing protocol to enhance the overall rearing performance.     

Unilateral eyestalk ablation improves molting frequency and reproduction in Macrobrachium amazonicum females

This study has investigated the influence of unilateral eyestalk ablation on the survival, molting frequency, fecundity, reproductive output, and fertility of M. amazonicum females. We divided 96 females into with ablation and without ablation groups with six replicates. Water quality, growth, survival rate, intermolt period, molts number, and ovigerous females over a 90-day period were monitored. Unilateral eyestalk ablation reduced intermolt period by 30% and increased molts number, ovigerous females, and reproductive output. Our findings indicate that unilateral eyestalk ablation positively influences reproduction in M. amazonicum and is appropriate for females of this species having a body length of ≥ 70 mm.     

Reproductive life history of the North American madtom catfish, Noturus hildebrandi (Bailey & Taylor 1950), with a review of data for the genus

Abstract– The female reproductive traits of a small, North American catfish were studied over a two-year period in a population at the southern extreme of the species'range. The reproductive season was long for Noturus , possibly from February to September. Females matured at age 1 and probably reproduced in only a single year. Clutch sizes were 16–68 oocytes in females 33–47 mm SL, and only one lifetime clutch may be produced. Clutch size, dry mass and volume were related to female size, but ripening oocyte size was not. Clutch mass averaged 23% of total body mass just prior to spawning. Compared to a northern population, females had greater SL-adjusted body masses, clutch sizes and clutch volumes but smaller oocytes. Oocyte size accounted for 73% of the difference in clutch sizes and clutch volume 14%. Concerns about the comparability of present data for Noturus are expressed. The need to include many life-history traits, from several populations of each species, using standardized methods in analysis of functional responses is discussed.     

Laboratory-based reproduction success of ruffe, Gymnocephalus cernuus (L.), in brackish water is determined by maternal properties

Abstract – Body length, age, egg size, embryo salinity tolerance and length at hatching of the freshwater (salinity <0.1 ppt, Lake Peipsi) and brackish-water (salinity 2–6 ppt, Pärnu and Matsalu Bay) ruffe, Gymnocephalus cernuus (L.), were examined to reveal their reproductive success in moderate salinity. Eggs of females originating from brackish water were significantly larger than eggs of freshwater females. No correlation between egg size and female size and age was found in brackish-water populations. In the freshwater population there was a small negative correlation between egg size and female size, but no correlation with female age. Fertilisation by sperm of males of different origin (brackish water or freshwater) produced no significant differences at any critical developmental stage (fertilisation, gastrulation, hatching) in the development of eggs from brackish-water or freshwater females at 3.3, 5.5, 7.7 and 9.9 ppt salinity. Survival rates in different salinity depended only on female origin; embryonic salinity tolerance was higher in ruffe inhabiting brackish water. Obviously, embryo salinity tolerance in ruffe is determined by egg qualities.     

Artificial fertilization and generating families for a selective breeding programme of large yellow croaker ( Larimichthys crocea )

Large yellow croaker is an important marine aquaculture species in China. The aim was to determine an appropriate protocol of artificial fertilization for family construction in the breeding programme based on two trials. In trial 1, luteinizing hormone-releasing hormone A3 (LHRHA3) was injected once, with a dosage of 2 μg/kg for females and 1 μg/kg for males. The latency time was in the range of 30–34 h. The maturation stage was checked by extracting a few eggs with a Pasteur pipette. The fertilization rate and hatching rate were 27 and 52%, respectively. The percentage of females with spawning difficulties was 30%. In trial 2, the females were injected LHRHA3 twice: with a first dose of 0.8 μg/kg and a second dose of 2 μg/kg, at an interval of 10 h, whereas the males were still injected once. The latency time was in the range of 29.5–35 h, determined by only observing courtship behaviour of males. The females with spawning difficulties decreased to 10%, and the fertilization rate and hatching rate also improved to 41 and 62%, respectively.     

Maturation and spawning of <Emphasis Type="Italic">Spratelloides gracilis</Emphasis> Clupeidae in temperate waters off Cape Shionomisaki,central Japan

ABSTRACT:   The reproductive ecology of Spratelloides gracilis was investigated in the temperate waters off Cape Shionomisaki, central Japan. Cape Shionomisaki is located at the northern margin of the distribution range of this species. Females of S. gracilis with gonadosomatic index (GSI) ≥ 4.0 were defined as mature based on the relationship between GSI and the histological maturity phases of their ovaries. More than 50% of females greater than 60 mm standard length (SL) were mature. Hatch dates of larvae and juveniles collected in the study area were determined by otolith daily ring counts and found to extend from April to November. The size at maturity of females (60 mm SL) and the spawning season of S. gracilis in the temperate waters off Cape Shionomisaki (April–November) was larger and shorter, respectively, than those in tropical waters in the western Pacific. The reproductive traits observed for S. gracilis off Cape Shionomisaki appear to be adaptive to northern temperate waters with seasonal changes in environmental conditions.     

Reproductive biology of male skipjack tuna <Emphasis Type="Italic">Katsuwonus pelamis</Emphasis> (Linnaeus) in the tropical western and central Pacific Ocean

The reproductive biology of male skipjack tuna Katsuwonus pelamis was examined from May 2005 to December 2007 in the tropical western and central Pacific Ocean. Testis maturity was classified into five stages (i.e., immature, early maturation, mid maturation, late maturation, and regression) on the basis of morphological changes in the germinal epithelium. The testis duct system (TS), which was characterized by lobules that lack spermatocysts, store only sperm, and form an anastomosing network, was located under the main sperm duct. The TS was observed at all stages of maturity except the immature stage, and first appeared in individuals with a fork length (FL) of 38–40 cm. The estimated minimum size at first maturity was 35.5 cm FL and the size at 0.5 maturity was 40.7 cm in FL. It was difficult to clearly differentiate the testis maturity stage based solely on the gonad index (GI) class because each GI class contained mature fish. Monthly changes in testis height index and GI did not follow a seasonal cycle. Mature individuals dominated throughout the year. These results imply that male skipjack tuna in this area showed evidence of spawning activity throughout the year without a clear seasonal pattern.     

Heritability estimates for processing and quality traits in common carp (Cyprinus carpio L.) using a molecular pedigree

Heritability estimates with a microsatellite parentage assignment based pedigree are of special interest in common carp cultured under traditional pond conditions. This method reduces common environment effects as all families can be grown immediately after hatching mixed in the same pond. We applied this method to study genetics of growth and processing traits in common carp at market size (1.5 kg and more). The experimental progeny was established by crossing 147 two-year old males and 8 females (six to eight-year old) of Hungarian synthetic mirror carp population. The fish grew up through three vegetation seasons and at the end a sample of 331 fish was examined for biometrical traits (standard length, body weight, relative head length, relative body height, relative body width), percent fat and processing traits (% processed body, % fillets with skin, % fillets without skin). It was shown that sex had a significant effect on most traits: females were larger and fatter than males, and they had both higher percent processed body and percent fillet with skin. Standard length, body weight, percent fat and relative head length had a high heritability (> 0.5), while relative body height, relative body width, percent processed body and fillet yields had a medium heritability (0.2–0.5). We found relatively high positive genetic correlations between body size (standard length and body weight) and percent fat (0.71 and 0.59, respectively), favourable genetic correlations between body size and percent processed body (0.69 for standard length and 0.74 for body weight) and between body size and fillet yields (0.50–0.77). Genetic correlations between body size and body shape (relative head length, relative body height and relative body width) were weak to moderate, thus selection for better growth should have little impact towards more rotund shape. Relative head length had strong negative correlation (− 0.7 to − 0.9) with percent fat, percent processed body and percent fillet yields. This means that indirect selection for reduced relative head length should be effective in improving of fillet yield.     

Maturity and reproduction of goneplacid crab <Emphasis Type="Italic">Carcinoplax vestita</Emphasis> (Decapoda,Brachyura) in Tokyo Bay

ABSTRACT:     Sexual maturity, morphological sexual dimorphism, and reproduction of the goneplacid crab Carcinoplax vestita were investigated in Tokyo Bay, Japan, from November 2002 to October 2003. The puberty molt in males was evidenced by changes in the relative size of the chelipeds and merus of the walking legs, and was estimated to occur at a size range of 13.20–18.85 mm carapace length. Post-pubertal females were identified by the relative size of the abdomen and puberty was estimated to occur at a size range of 12.81–15.46 mm carapace length. Sexual dimorphism in C. vestita was observed in all features that showed secondary sexual characteristics. Monthly changes of gonad index in males, and of seminal receptacle index and occurrence of sperm plugs in females were synchronized, and indicated that mating was intense in spring. Ovaries began developing in March. Ovigerous females were found in all months except December, but were clearly more abundant between August and October. Fecundity ranged from 7800 to 57 000 mature oocytes per female per batch and was highly correlated with body size. The results suggest that some females may spawn more than one batch per year.