Parentage assignment in hatchery population of brown sole <Emphasis Type="Italic">Pleuronectes herzensteini</Emphasis> by microsatellite DNA markers

ABSTRACT:   Five loci ( Phz2 , Phz6 , Phz7 , Phz12 , and Phz14 ) of microsatellite DNA markers developed in a previous study for parentage assignment in the hatchery population generated by mating among 61 broodstock fish (35 females and 26 males) in a spawning tank, were selected. After natural spawning in the same tank, larvae collected at three different times were categorized into early phase (EP), middle phase (MP), and late phase (LP) groups. In the parental broodstock, the mean number of alleles per locus was 21.8 and expected heterozygosity ( H _E ) was 0.813. In the progeny, the mean number of alleles per locus decreased to 11.6 (EP), 14.4 (MP), and 6.4 (LP) and H _E to 0.796 (EP), 0.833 (MP), and 0.681 (LP). Parental assignment determined eight dams and six sires as major parents for the EP group. In the MP group, 13 dams and ten sires genetically contributed to spawning, but only three dams and two sires were involved in LP group progeny. In the hatchery population produced from a limited number of parental fish such as the LP group, genetic variability was apparently decreased.     

Microsatellites markers to depict the reproductive and genetic patterns of farmed gilthead seabream (Sparus aurata): illustration by a case study on mass spawning

In the absence of breeding strategy, natural spawning constitutes the breeding ground for fish farmers to empirically manage their commercial broodstock. In this context, we used six microsatellite markers to characterize the genetic pattern of six commercial seabream broodfish tanks having a common history spanning four generations. The progeny of one tank single‐day mass‐spawning event, reared in two different environments, was used to estimate the genetic parameters for body weight. Limited genetic differentiation was observed among broodfish groups. A panel of nine loci allowed us to unambiguously assign 95.4% of the offspring (1692) and identify 37 parents (65% of the total broodfish). The limited effective population size (N_e = 15.3) was due to the elevated variance of parental contributions and to broodfish failing to contribute to the progeny. The fluctuation of the allele frequency highlighted the risks of genetic drift and reduction in the heterozygosity in the next generations. Heritability for body weight was moderate at commercial size (0.40 ± 0.10) and the high genetic correlation at later stages laid the groundwork for precocious selection criteria for growth. The discussion opens on the opportunity to use mass spawning for selective breeding.     

Parentage Determination and Effective Population Size Estimation in Mass Spawning Pacific Oyster,Crassostrea gigas,Based on Microsatellite Analysis

Seven high polymorphic microsatellite loci were used to determine the pedigrees in a mass spawning of Pacific oyster, Crassostrea gigas, and to estimate the genetic variability between broodstock and offspring. Parental assignment was performed on a total of 155 individuals, including 141 offspring, 8 candidate mothers, and 6 candidate fathers. The assignment results of real offspring were generally in agreement with simulation with a success rate over 99% using only six of these loci. The allelic diversity and observed heterozygosity (H_o) exhibited similarity between parents and offspring populations, but the expected heterozygosity (H_e) had a significant decrease in offspring. Although all the males and females contributed to the next generation, the variances of reproductive success and unequal sex ratio resulted in a decline in effective population size (N_e = 11.42). The inbreeding rate of this small‐scale, mass spawning population was estimated at approximately 16.5% per generation. This gave us an insight that when designing breeding programs based on mass spawning for future oyster cultivation generations, the higher inbreeding and lower effective population size should be considered.     

Estimating reproductive success of brooders and heritability of growth traits in Asian sea bass (Lates calcarifer) using microsatellites

Asian sea bass (Lates calcarifer) is one of the most important marine food fish species in Asia and Australia. To estimate the reproductive success of broodstock and heritabilities of growth‐related traits, two independent full‐factorial crosses (PI and PII) were created by crossing 10 males and 10 females. At 90 days post hatch (dph), the body weight (BW) and total length (TL) of 804 individuals from PI and 900 individuals from PII were measured and tissues samples of each fish were collected. Parents and offspring were genotyped with nine polymorphic microsatellites. Out of 1704 offspring from the two crosses, 98.7% were assigned to their parents. In PI, 19 of 20 parents produced offspring, while in PII, only five parents contributed to offspring. Low contribution of parents to offspring could lead to reduced genetic variation in the next generation. Heritabilities for growth‐related traits were estimated using the pedigrees reconstructed using microsatellite genotypes. The estimates of heritability were 0.22±0.16 and 0.25±0.18 for BW, 0.31±0.14 and 0.24±0.21 for TL and 0.22±0.22 and 0.15±0.09 for Fulton's condition factor in the two crosses respectively. Body weights at 90 dph and at harvest (289 dph) were significantly correlated (r=0.601, P<0.01). Therefore, growth‐related traits could be improved by exploiting additive genetic effects through selective breeding, and broodstock candidates could be selected early in the production cycle.     

Parentage assignment of stocked black sea bream <Emphasis Type="Italic">Acanthopagrus schlegelii</Emphasis> in Hiroshima Bay using microsatellite DNA markers

The genetic contribution of 51 broodstock, comprising 29 females and 22 males, reared at Hiroshima City Marine Products Promotion Center for the production of stocked black sea bream was monitored during two consecutive years using seven microsatellite DNA loci. The high discrimination ability of these markers was reflected in the polymorphic identification content (PIC=0.831), the exclusion probability (Q≈1), and the low probability of identity index (I=3.635⁻¹⁰). The total number of breeders contributing to the mating process was estimated at 32 (62.7%) in 2000 and 30 (58.8%) in 2001. On pedigree reconstruction, 69.3% of the offspring were successfully assigned to a single broodstock pair. Loss of alleles accounted for 16.9% during seed production; nevertheless, 90.9% of males and 69.0% of females participated in the mating process. Based on microsatellite genetic tagging, 58.9% of the fish sampled during the two months after release were identified as hatchery stock, presenting no significant differences from wild conspecifics in either fork length or body weight.     

Evaluation of a novel pentaplex microsatellite marker system for paternity studies in Atlantic cod (Gadus morhua L.)

Five Atlantic cod (Gadus morhua L.) microsatellites (Gmo8, Gmo19, Gmo35, Gmo37 and Tch11) were selected for parentage assignment. All markers were co‐amplified using dye‐labelled primers and sized by automated sample processing in a 3130xl Genetic Analyser. The genotyping of samples was reproducible and alleles from all loci could be genotyped confidently (precision and accuracy above 99.7 and 99.1% respectively). The number of alleles, observed allelic and genotypic frequencies were calculated. A population database was established for fish originating from randomly selected wild‐caught Norwegian coastal‐ and North‐East Arctic cod. Combined paternity exclusion and the probability of match were 99.97 and 1.5 × 10^?9 respectively. The multiplex assay system was used successfully for parental assignment of 2336 juveniles from different mass spawning breeding tanks. Of all offspring, 91.2% were assigned to a single parental pair. In total, 523 different matings were recorded, and 69 of 70 dams and all of the 30 sires contributed to the offspring.     

Natural Spawning of Captive Bigeye Scad Selar crumenophthalmus in Hawaii

Abstract.— Juvenile bigeye scad Selar crumenophthalmus were caught from the wild by hook and line and reared over 3 yr to establish a spawning broodstock of this species. The size at first maturity for captive males and females was 19-cm and 25-cm fork length (FL). Natural spawning of captive individuals occurred during the first year in captivity. The broodstock were observed to spawn repeatedly throughout their second and third years in culture. This species is a multiple spawner producing approximately 96 × 10³ to 121 × 10³ eggs/spawning group, 5 to 10 times per year. Stocking densities of 1–8 individuals/m³ were found to be suitable for natural spawning to occur. Collectively, the results indicate that this species exhibits notable potential for artificial propagation.     

Meat and Bone Meal as an Alternative for Fish Meal in Soybean Meal‐Based Diets for Florida Pompano,Trachinotus carolinus L.

Alternative protein feedstuffs are potential surrogates for fish meal in the diet of Florida pompano. This study was designed to evaluate the replacement of fish meal with meat and bone meal in a soybean meal‐based diet for Florida pompano. In Trial I (10 wk), the basal diet (FM15, formulated to contain 40% crude protein and 10% lipid) containing 15% fish meal was modified by the isonitrogenous replacement of fish meal with meat and bone meal producing diets with 10 (FM10), 5 (FM05), and 0% (FM0) fish meal. In Trial II (8 wk), the FM0 served as the basal diet (Tau 0) and was modified by the additive supplementation of taurine to produce three test diets containing 0.25 (Tau 0.25), 0.5 (Tau 0.50), and 0.75% (Tau 0.75) taurine. In Trial I, reduced weight gain (220.1%), feed efficiency (0.31), and survival (84.5%) were observed in fish fed the FM0 diet (P < 0.05). In Trial II, the supplementation of taurine improved the growth performance, survival, and protein and energy retention efficiencies of Florida pompano (P < 0.05). These results indicate that the supplementation of taurine was required in these feed formulations and that meat and bone meal is a good alternative ingredient for fish meal in soybean meal‐based diets for Florida pompano.     

Loss of genetic diversity due to hatchery culture practices in barramundi (Lates calcarifer)

Many aquaculture hatchery practices are detrimental to the long-term viability of restocking and selective improvement programs. Small effective broodstock population sizes, differential broodstock contribution, differential larval/juvenile survival during metamorphosis and size-based grading, all have the potential to drastically reduce the level of genetic variation remaining in hatchery populations. Monitoring levels of genetic variation and maintaining detailed pedigrees on progeny is the key to circumventing these problems. In this study we used microsatellites, coupled with DNA parentage analyses, to track the loss of genetic diversity in two independent commercial barramundi (Lates calcarifer) hatcheries over three mass spawning events, where up to two females and seven males had the opportunity to participate. Initial broodstock contributions were observed to be highly skewed, with significant differences observed in both the level of contribution by females to each mass spawning, as well as in the number of males participating and subsequently contributing to the genetic composition of cohorts. Effective population sizes were around half that of census sizes. We then examined whether differential family survival through metamorphosis (27 days post-hatch) and/or first size grading further influenced the retention of genetic diversity levels initially sampled during spawning. Parentage analyses indicated that some families that had been initially represented in cohorts had been lost, or that the contribution by particular broodstock had changed. In one cohort, as many as 55% of progeny were found to be sired by a single male individual. Size grading was also found to potentially impact on genetic diversity, with data suggesting that family representation in each of the grades was non-uniform and that some families were on average faster or slower growing than others. These results illustrate that hatchery management practices have the potential to significantly impact on the retention of genetic diversity in this species.     

Hormone manipulation to overcome a major barrier in male catfish spawning: The role of oxytocin augmentation in inducing voluntary captive spawning

A major challenge in Clariid catfish seed production is our inability to induce voluntary captive spawning of the brooders. Since voluntary captive spawning had been previously elicited in a Clarias species by simulating natural breeding environment, we speculated that the major obstacle in voluntary spawning might be the absence of an inducing agent that triggers mating response in the brooders. To address the issue, oxytocin was injected to the brooders along with Ovatide (a commercial inducing agent comprising salmon gonadotropin‐releasing hormone analogue and domperidone). Administration of 40 mIU/kg body weight of oxytocin after 12 hr of Ovatide injection resulted in voluntary spawning of the fish (81.5%, i.e. 31 out of 38 trials), with more than 70% hatching rate in simple and low‐cost spawning facilities. Histology of male gonads indicated sustained gamete maturation and the gonads were observed to be visibly turgid in the fish that received both the hormones. In contrast, gamete maturation slackened after 10 hr in the control fish, injected with Ovatide only. Administration of oxytocin along with Ovatide was also observed to induce aggressive sexual behaviour among the males. Neither of the hormones, acting alone, could induce voluntary spawning in the fish or influence sexual behaviour. Our results clearly show that oxytocin plays a significant role in sustaining the male gamete maturation induced by Ovatide and trigger the behavioural mating response, leading to voluntary spawning in C. magur. The results hold potential to make a paradigm shift in the commercial catfish seed production technology.     

Reproduction of striped bass, Morone saxatilis (Walbaum), broodstock: monitoring maturation and hormonal induction of spawning

Abstract Levels of gonadal steroid hormones were quantified in an adult striped bass, Morone saxatilis (Walbaum), broodstock during their gametogenic cycle. Blood plasma concentrations of Estradiol (E₂) and testosterone in females, or 11-ketotestosterone(11-KT) and testosterone (T) in males, were used as indicators of maturation. In both sexes, hormone levels were low in summer but increased significantly by late October to intermediate levels which were then maintained until late January. They then increased again rapidly to maximum pre-spawning values attained in late February or March, and subsequently decreased during the spawning period (April and May) with an increased incidence of spent fish with low hormone levels. The changes in blood hormone concentrations coincided with annual changes in photoperiod and water temperature that may be useful landmarks for maturation in captive broodstock. Mature females were implanted with pellets containing a dose of approximately 20 μg/kg body weight of [D-Ala⁶-Pro⁹-Net]-LHRH (GnRHa) in a matrix of cholesterol (CH) and cellulose. In April, they had not yet begun final oocyte maturation (FOM) and were too immature for conventional induction of spawning by injection with human chorionic gonadotropin (hCG). In early April, females given two 95% CH (slow hormone-release) GnRHa pellets (95/95) or females given one 80% CH (fast hormone-release) GnRHa pellet and one 95% CH GnRHa pellet (80/95) spawned within 13 days treatment (n= 4) with good egg fertility (76 ± 7% of total) and hatch rates (62 ± 15% of fertile). Females given dual fast-release GnRHa pellets (80/80) or control (Sham) pellets did not spawn or show evidence of increased oocyte diameter or development. In late April, four of six females given the 80/95 GnRHa pellet combination spawned within 9 days. Three fish produced fertile eggs (54 ± 18%). one spawned overripe eggs, and the remaining two increased oocyte diameter and maturation. Three corresponding controls did not spawn, and two of these showed clear signs of atresia within 11 days. In early May, some females were undergoing early FOM and were mature enough to be spawned by hCG injection. Three were given a single 80% CH GnRHa pellet and spawned within 6 days of treatment to produce fertile eggs (44 ± 6%). Of two other females given dual 80% CH GnRHa pellets, one spawned infertile eggs and the other failed to spawn within 9 days. GnRHa implants show promise as a technique for inducing spawning of captive striped bass broodstock although the optimum hormone delivery systems, dosages and release rates should be verified for fish at specific maturational stages.     

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.     

Progress Toward Year-round Spawning of Southern Flounder Broodstock by Manipulation of Photoperiod and Temperature

Reliable methods have been developed for controlled spawning of captive southern flounder, Paralichthys lethostigma, broodstock during their natural winter (December–February) spawning season. From 1999 to 2004, we evaluated the effects of manipulation of photoperiod and temperature on both advance and delay spawning to produce viable embryos throughout the year. Wild‐caught adult broodstock were held in 4.8‐ to 7.0‐m³ controlled‐environment tanks at a sex ratio of approximately 12 females to 4 males. Broodstock were subjected to different artificial photothermal conditioning regimes: extended winter (EW), accelerated (A‐10‐, A‐6‐, A‐4.5‐, and A‐3.8‐mo regimes), and delayed (D‐16‐ and D‐14‐mo regimes), with gradual and abrupt transitions, respectively, from long to short daylengths. Under an EW cycle, fish were exposed to constant short daylengths (10 L: 14 D) after the winter solstice in January. Eighty‐seven natural spawnings from December to April produced 18.3 × 10⁶ eggs, with 20.9% hatching successfully (i.e., overall egg viability). Under an A‐10‐mo cycle, rate of decrease in daylength was accelerated after the summer solstice in July, to reach winter conditions in October. Seven induced spawning trials from October to November produced 897 × 10³ eggs, with 40.4% viability. Under an A‐6‐mo cycle, rate of change of photoperiod was accelerated after the winter solstice in January, to reach winter conditions in July. Three induced spawning trials in July produced 550 × 10³ eggs, with 14.7% viability. Under an A‐4.5‐mo cycle, broodstock exposed to EW from January through April were exposed to an accelerated cycle to reach winter conditions by October. Four induced spawning trials from September to November produced 729 × 10³ eggs, with 28.7% viability. Under an A‐3.8‐mo cycle, broodstock exposed to EW conditions from January through April were exposed to an accelerated cycle to reach winter conditions by September. Five induced spawning trials from September to November produced 510 × 10³ eggs, with 45.9% viability. Under a D‐16‐mo cycle, fish were exposed to a decelerated decline in photoperiod after the summer solstice in July, to reach winter conditions in May, when atretic females were observed. Under a D‐14‐mo cycle, fish were exposed to constant summer conditions from December through mid‐June and then to an abrupt decline in photoperiod to winter conditions in late June. Six induced spawning trials from September to November produced 763 × 10³ eggs, with 13.0% viability. Production of viable embryos was greatest during the extended winter because of abundant natural spawnings. While successful natural spawnings were rare during the fall or summer, viable embryos were produced through induced spawnings during all seasons of the year, with no significant (P > 0.05) differences in egg viability. Extended winter conditions prolonged spawning from 3 to 5 mo. Accelerated (3.8–10 mo) regimes were effective in producing viable embryos from summer through fall, but a minimum of 5 mo was required to complete gonadal recrudescence. While constant long daylengths after the summer solstice delayed gonadal recrudescence, with spawning obtained 2.5 mo after an abrupt reduction to short daylengths, a decelerated decline in photoperiod did not. Artificial control of daylength enabled precise control of gonadal recrudescence and year‐round spawning in southern flounder without adverse effects on the quality of eggs and larvae and will improve availability of seedstock for commercial aquaculturists.     

Male antagonistic behaviour after spawning suggests paternal care in brown trout,Salmo trutta

Abstract – The evolution of parental care depends on the sex‐dependent resolution of a trade‐off between present and future reproduction. In salmonids, the mating systems are often characterised by fierce male–male competition, and the absence of paternal care is widely admitted in these species. However, the fact that brown trout eggs can be cannibalised by peripheral individuals just after spawning suggests that dominant males would benefit from protecting their offspring by keeping cannibals away from the nest. We used 77 field observations of brown trout spawning to document the defensive behaviour of dominant males towards peripheral individuals before and after spawning, and test whether this behaviour was related to the probability of the clutch being cannibalised. We showed that dominant males stayed on the nest and chased peripherals even after the eggs were laid and fertilised. The number of chases performed by dominant males during the 2 min following spawning was negatively correlated to the probability of egg cannibalism. This result indicates that brown trout males can provide direct benefits to females through protection against egg cannibalism by peripheral individuals.     

Parentage assignment in hybrid abalones (Haliotis rufescens × Haliotis discus hannai) based on microsatellite DNA markers

Parentage analysis in aquaculture determines genealogical relationships between broodstock and progeny when the parents are unknown. Thus, parentage analysis is a useful tool to establish pedigree reports in molecular‐assisted selection programs. Here, we evaluated 10 heterologous microsatellite markers for parentage assignment in abalone hybrids produced from 43 abalone broodstocks of red abalone (Haliotis rufescens) and Japanese abalone (H. discus hannai). The allele frequencies, exclusion probabilities and broodstock contributions were calculated using CERVUS, PAPA and GERUD software. The polymorphic information content (PIC) values showed that most of the microsatellite loci were highly informative (>0.7) and more than 90% of parentage assignment was possible with a minimum of 5–6 microsatellite markers. Parentage assignment for hybrid and pure‐red progeny showed a better performance than pure‐Japanese progeny. This result could be due to the high level of allele loss in the parental genotypes. In addition, results indicated that only two sires contributed over 80% and 90% of red and hybrid progenies, respectively. This study gives a new molecular tool to support marker‐assisted selection in abalone hybrids produced in Chile.     

Effects of soybean meal replacement with fermented soybean meal on growth,serum biochemistry and morphological condition of liver and distal intestine of Florida pompano Trachinotus carolinus

This study evaluated the suitability of commercially produced fermented soybean meal (FSBM) known as PepSoyGen?, in a plant‐based diet for Florida pompano, Trachinotus carolinus fingerlings. An 8‐week growth trial was conducted to evaluate the effect of four isonitrogenous and isolipidic diets containing 0, 206, 309 and 410 g/kg FSBM, replacing approximately 0%, 50%, 75% and 100% SBM (designated as Basal, FSBM 50, FSBM 75 and FSBM 100, respectively) on growth performance, body composition, serum biochemistry and morphological condition of liver and distal intestine of Florida pompano. There were no significant differences in final mean weight, percentage weight gain, thermal unit growth coefficient and feed conversion ratio in all treatments. For serum biochemistry analysis, there were no significant differences in total protein, albumin, glucose, cholesterol, bile acids, plasma alkaline phosphatase, alanine aminotransferase and aspartate aminotransferase activities in all treatments. Cellular infiltration, presence of goblet cells and the width of lamina propria in the distal intestine were partly improved in fish fed FSBM 75 and 100 compared to the fish fed FSBM 50 and basal diet. Glycogen granulation, inflammation and nuclear change condition in the liver of pompano were better as the inclusion of fermented product increased. Results of this study indicate that FSBM can be utilized as an alternative protein source and microbial fermentation process could improve the functional properties of SBM.     

Beef tallow is suitable as a primary lipid source in juvenile Florida pompano feeds

It is assumed that Florida pompano have dietary EPA (20:5n‐3) and DHA (22:6n‐3) requirements. However, it is unclear whether both are equally important in meeting demand for n‐3 long‐chain polyunsaturated fatty acids (LC‐PUFAs) or whether the requirement(s) can be influenced by other fatty acids. Accordingly, we assessed production performance and tissue composition of juvenile Florida pompano (41.0 ± 0.5 g) fed diets containing fish oil; beef tallow; or beef tallow partially or fully supplemented with EPA, DHA or both. After 8 weeks, no signs of fatty acid deficiency were observed. Although fish performance did not vary significantly among the dietary treatments, fish fed the DHA‐supplemented feeds exhibited numerically superior growth than those fed the other diets. Fillets of fish fed the beef tallow‐based diets contained reduced levels of n‐3 fatty acids and LC‐PUFAs and elevated levels of MUFAs and n‐6 fatty acids, although dietary supplementation with EPA and/or DHA attenuated these effects somewhat. Our results suggest that beef tallow is suitable as a primary lipid source in Florida pompano feeds and n‐3 LC‐PUFA requirements may be met by as little as 4 g/kg EPA and 4 g/kg DHA. However, there may be value in supplementing tallow‐based diets with DHA to enhance tissue levels and possibly growth.     

Parental Contributions in a Japanese Flounder Hatchery Inferred from Mitochondrial DNA Haplotypes

We analyzed a portion of the mitochondrial genome of hatchery Japanese flounder Paralichthys olivaceus to compare the genetic characteristics between maternal parents and their offspring. The maternal parents consisted of 11 subcultured fish (broodstock taken from hatchery-raised fish) and 41 wild fish. A 1098 base pair region extending from the 3'half of the cytochrome b gene to the central domain of the control region of mtDNA was amplified by PCR and analyzed using 11 restriction endonucleases. We also analyzed the number of copies of tandem repeats in the control region from the sizes of the PCR products. Each female parent had a unique haplotype, but only 31 of them were observed among the 66 offspring examined. From these results, we estimated that about 60% of the maternal parents in the hatchery contributed to the offspring we surveyed. The distribution of the family sizes of the wild fish was Poisson, which is consistent with expectation from a randomly mating population. In contrast, the distribution of family sizes of the subcultured fish deviated from a Poisson distribution. One of the sources of the deviation was that none of the six oldest fishes contributed to offspring production, which is consistent with observation that the spawning peaks later in the spawning season for older fish in flounder hatcheries. Uneven contribution of the female flounders in the hatchery has the potential to reduce substantially the genetic diversity in the offspring. Our results suggest that the misuse of subcultured fish as broodstock is an important cause of reduced genetic diversity in hatchery-raised flounder juvenile.     

Fructose 1,6 bisphosphatase activity in liver and gonads of sea bass (Dicentrarchus labrax). Influence of diet composition and stage of the reproductive cycle

The fructose 1,6 biphosphatase (FBPase) activity was measured in the liver and gonads of broodstock sea bass that were fed three experimental diets over the reproductive cycle. Enzyme activity was measured at the pre-spawning (November), spawning (February) and post-spawning (May) periods. Additionally, some biometric indices were calculated at these three times. The different diets, one with standard composition (51% protein, 13% lipid, 10% digestible carbohydrates), one with a high-carbohydrate content (32% protein, 13% lipid, 32% digestible carbohydrates) and one deficient in ω3 essential fatty acids (51% protein, 13% lipid, 10% digestible carbohydrates), had similar affects on growth and gonad development, as deduced from the similar weight, condition factor, hepatosomatic index, gonadosomatic index and liposomatic index over the reproductive cycle. FBPase activity was detected at all times in the liver of both sexes, and in the ovaries but not in the testes. In general, females showed greater liver activity than males, especially at spawning time. During post-spawning, FBPase activity fell in tissues of both sexes. Enzyme activity was also affected, mostly in the liver, by the different types of feed; hepatic activity in fish fed the high-carbohydrate diet fell during the spawning and post-spawning periods, though at a different level for each sex. The diet deficient in ω3 EFA presented the lowest FBPase activity, compared with the other diets, in females during the spawning period; there was very little change in males or females over the reproductive cycle. The results showed that the highest gluconeogenic activity in sea bass broodstock occurred at the spawning time and the females had larger glucose requirements than males over the reproductive cycle, as demonstrated by the absence of FBPase activity in testes. This work also confirmed the adaptative capacity of this enzyme to different nutritional and physiological conditions.     

Effects of dry pellets containing astaxanthin and squid meal on the spawning performance of striped jack Pseudocaranx dentex

ABSTRACT: This study was conducted to investigate the effect of squid meal and astaxanthin in dry pellets on the spawning performance of striped jack. Two groups of 8-year-old fish with an average bodyweight of 3.5 ± 0.4 kg were used. The control group was fed a raw fish mix (RF) and the experimental group was fed steam dry pellets (as-DP) containing 10 p.p.m. astaxanthin and squid meal, the latter replacing half the fish meal. Each group was fed once a day, three times a week in floating net cages for a period of 5 months. Seven females and seven males were selected from each group and transferred to 65 m³ indoor concrete tanks for spawning, where they were kept at optimum spawning conditions (22°C) for 1 month. The average bodyweights of selected fish were 3.8 ± 0.5 kg and 3.8 ± 0.6 kg for the RF and as-DP groups, respectively. Both groups spawned a total of 18 times and the mean total egg production and egg quality, measured in terms of buoyancy, fertilization and hatching rates, showed no significant differences ( P > 0.05) between groups. Total larval production was 679.9 × 10³ and 678.1 × 10³ larvae/kg-female for the RF and as-DP groups, respectively. These results show that the combination of astaxanthin and squid meal in dry pellets for striped jack broodstock improved the overall spawning performance to a level similar to that of fish fed on RF.