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This study aimed to investigate how supplementation of glutamate to high and low energy Atlantic cod ( Gadus morhua ) diets, affects fish performance, muscle quality and lipid metabolism. This was investigated by feeding Atlantic cod extra dietary glutamate (0.2%) supplementation at two different fat levels (13 and 24% total fat) for a period of 94 days (weight increased from 200 g to 425 g). Overall, only marginal effects of glutamate supplementation could be observed at both fat levels. Differences between groups were mainly explained by fat level in the diet and not by glutamate. Higher fat level reduced feed conversion rate and increased hepatosomatic index (HSI) and hepatic fat content. However, a quality parameter like fillet lightness was significantly increased by glutamate in the low fat group whereas fillet firmness was increased by glutamate in the high fat group. Metabolic studies in isolated liver cells revealed a tendency for increased β-oxidation and lower deposition of lipids in the liver cells from Atlantic cod fed with extra glutamate. PPARα was also upregulated in hepatocytes from glutamate fed Atlantic cod. QPCR analysis of transcripts for key metabolic genes in tissues like intestine, liver or muscle revealed almost no gene regulatory effects of dietary lipid or glutamate levels. Supplementation of Atlantic cod diets with extra glutamate may therefore have the potential to improve the quality parameters like color and firmness without compromising growth and health of the animals.

Within the aquaculture industry downgrading losses due to poor quality represent large costs to the producers, and an interest in implementing quality parameters in breeding goals has therefore emerged. Through genome-wide association studies (GWAS) one can identify genetic variation affecting quality parameters, which can in turn facilitate efficient implementation in breeding schemes by use of marker-assisted selection. This study aimed to identify genetic variation affecting fillet fat content and fillet firmness in farmed Norwegian Atlantic salmon using 5650 genome-wide distributed SNPs. Phenotypic records from instrumental analyses of fillet fat content and fillet firmness were retrieved from fish provided by a commercial Norwegian breeding company and implemented in GWAS. Further, genome partitioning by estimation of variance components for individual chromosomes based on SNPs was conducted for the purpose of validating results from GWAS. Combined the results from GWAS and genome partitioning suggested that genetic variation affecting fillet fat content is present on Atlantic salmon chromosomes 9 and 10, and that genetic variation affecting fillet firmness is present on Atlantic salmon chromosomes 3 and 11.

Atlantic cod with an average initial weight of 413 g were fed for 112 days diets containing either 11.4 or 30.5% lipid (of dry matter) until they reached a final weight of approximately 750 g. Samples of intestine, liver and blood were taken at the end of the feeding period, and then after 3 weeks of fasting. The lipid level in the diet did not significantly affect fish growth. The hepatosomatic index (HSI), however, increased by a factor of 1.5, and the liver lipid index by a factor of 1.7, when fish were fed the high-fat diet. The increase in HSI was primarily due to a larger average size of liver cells, due to a higher level of lipid deposition than in the livers of fish fed the low-fat diet, which had more and smaller liver cells with less lipid. Vesicles with the size of very low density lipoproteins (VLDLs) were found in liver cells of fish fed the high-fat diet. In fish from the same dietary group, vesicles with the size of chylomicrons were found in intestinal enterocytes. These particles were however not present in tissues from fasted fish. The cholesterol and protein rich high density lipoprotein (HDL) was the predominant lipoprotein class in cod serum, with the triacylglycerol (TAG) rich low density lipoprotein (LDL) as the next most common class. Some TAG-rich VLDLs and chylomicrons were also present in the serum. The apo-lipoprotein compositions of the lipoprotein classes in cod were similar to those of other species: the apoB was the major protein in chylomicrons, VLDLs and LDLs, while apoA predominated in HDLs. There was a tendency to reduced liver lipid index in fasted fish, indicating lipid mobilisation from the liver. The fatty acid (FA) serum profile showed an increased percentage of saturated FAs, while there was a reduction in the percentage of saturated FAs in the liver with fasting, indicating a higher mobilisation of saturated FAs relative to other FAs. The increased degree of blood capillary vascularisation (angiogenesis) found after fasting is likely to improve the supply of nutrients and FAs from the liver via serum to other organs and tissues. Mobilised lipids were mainly transported esterified in TAG, primarily in HDL, less in LDL.

The simulation study examined the effect in optimal contribution selection of specifying an additive genetic relationship matrix (A-matrix) deviating from the true A-matrix of the base population. A base population of 160 males and 160 females was sampled evenly from 4 or 8 randomly chosen, drift-differentiated, wild subpopulations. Wild fish had true inbreeding coefficient of F wild , either 0.05 or 0.20, giving additive genetic relationships of 2 F wild within, and 0 between subpopulations. Selection based upon phenotypes was simulated on one continuous trait of heritability, h wild 2 , either 0.1 or 0.3. Base animals were mated either within subpopulations, or at random, so that the first round of selection occurred either on purebred or crossbred fish respectively. Optimum contributions was implemented from generation 1 for a desired rate of inbreeding of 0.5% per generation, using an assumed F wild ⁎ which varied between 0.0 and 0.3. Assuming F wild ⁎ = 0.0 compared to 0.3, resulted in steeper regressions of the fractional contributions of subpopulations on average breeding value, higher true inbreeding and consequently reduced additive genetic variance, albeit with larger genetic gain from the first round of selection. When the first round of selection followed random mating the regression of the fractional contributions of the subpopulations was also less steep. These effects persisted, but originated from the misspecification of F wild ⁎ and so will not accumulate further in the medium-to long-term. Consequently, assuming F wild ⁎ was less than the true value led to sub-optimal use of subpopulations with an increased risk of loss of alleles of direct and strategic relevance to the breeding program. In conclusion, assuming F wild ⁎ ≈ 0.0 should be avoided and F wild ⁎ should be estimated with procedures such as marker estimated kinships, Q ST estimates or empirical observations of clines.

Guidelines for constructing base populations in fish were examined using a drift model. A large number of drift differentiated, wild subpopulations, with inbreeding Fwild (Fwild ∈ [0.05–0.20]), and a trait with heritability htot2 (htot2 ∈ [0.10–0.30]), were assumed. A base population was generated by sampling 2N fish from each of nsub subpopulations (nsub ∈ [1–8]), and then mated to produce 160 or 240 families per generation. The matings were either at random, in a structured diallel-cross, or within subpopulations to produce generation 1. Optimal contribution selection on phenotype was applied from generation 1 to11, with a rate of inbreeding of 0.5% per generation. Genetic gain (Δg) improved with nsub, the improvement being largest when going from one to two subpopulations, with diminishing returns. Most of the potential improvement was obtained with nsub = 4, and was well predicted by Δ g nsub Δ g 1 ≈ ( 1 − F wild / nsub ) ( 1 − F wild ) . Initial matings across subpopulations improved Δg from the second round of selection compared to within. Consequently the effect of the mating strategy were first observed 3 generation after decisions were made and persisted over subsequent generations, but with minimal effect on the accumulated additive genetic gain in generation 11. It was concluded that sampling from at least four subpopulations was beneficial and that mating across subpopulations should start as early as possible.

The aim of this study was to estimate genetic parameters for resistance to infectious pancreatic necrosis (IPN) in Atlantic salmon and to evaluate the correlation between survival in challenge tests and survival in field outbreaks of IPN. The analyses were based on challenge test data from four sub-populations of fish. Challenge testing for resistance to IPN has been a part of Aqua Gen's breeding programme since 1997. Data from 8 years was included in the study, and a total of 271,366 fish were tested. Moreover, data from two field outbreaks were analysed. The heritabilities were found to be in the range 0.17–0.45 for each year analysed separately. All years analysed together gave an overall estimate of the heritability of 0.31. The genetic correlations between IPN challenge tests and IPN field outbreaks were found to be in the range 0.78–0.83. The results confirm that there is genetic variation for resistance against IPN in Atlantic salmon, and that a strong positive genetic correlation between IPN challenge tests and IPN field outbreaks exists.

Resistance to infectious pancreatic necrosis virus (IPNV) has been included in a commercial selection program for Atlantic salmon since 2001. The IPN selection is based on bath challenge tests of several hundred families of first feeding fry, and the breeding value for each family is estimated from the resultant cumulative mortality rate. Since IPN selection is based on breeding values estimated from the results of a challenge test, it is difficult to evaluate the selection response in the population from generation to generation. Although a heritability of 0.31 has been estimated (unpublished results), we wanted to confirm the effect of selection for IPN resistance. The trial was carried out in two experiments where two groups of first feeding Atlantic salmon fry and postsmolts were challenged with IPNV: A) Families selected for high resistance to IPN, denoted as HR. B) Families from the same breeding population as A) selected for low resistance to IPN, denoted as LR. Both groups were challenged in two different tests: i) in fresh water in seven replicate tanks (7 × 100 fry). ii) in sea water after smoltification in five replicate tanks. Cumulative mortalities in the groups were significantly different. Group B) had more than double the mortality than group A), both in fresh water and sea water. The average cumulative mortalities in the A)/B) groups were 29.3%/66.6% and 32.0%/79.0% in fresh water and sea water, respectively.

Fish-breeding programs may be based on fish from wild or from domesticated populations. The knowledge of the genetic properties of these populations is often poor. One alternative is to assume that all fish are unrelated, having the same genetic variance within subpopulations, but different genetic means. The effects of increasing the number of subpopulations in the base (1–8) and the mating design in the base (mating within subpopulations, or at random, within and across subpopulations) on genetic variance, genetic gain and the contributions of the different subpopulations in the following generations were studied for a base population with a realistic number of families (160 or 240) and a somewhat low number of offspring per family (20 or 30). Stochastic simulation was used, assuming an infinitesimal additive genetic model. Selection was carried out for 10 generations, applying optimal contribution selection on phenotype, which maximizes genetic gain at a fixed rate of inbreeding. The largest genetic gain was obtained when sampling fish from at least four subpopulations, and mating within subpopulation(s) in the base. Given a genetic variance within and between subpopulations of 0.2, increasing the number of subpopulations from one to four and from four to eight led to an improvement of the genetic level in generation 11 by 7.0% and 0.3%, respectively. Standard deviations of genetic level, i.e., risk, were also lower from sampling from a larger number of subpopulations. However, sampling from a larger number of subpopulations may introduce larger costs connected with sampling of fish from more locations.

The increased requirement for food fish, the lucrative market for expensive seafood, and the need to conserve marine resources, have motivated the rapid pace of larviculture research in Southeast Asia. Various research and academic institutions in Southeast Asia such as the Southeast Asian Fisheries Development Center Aquaculture Department (SEAFDEC AQD) are carrying out research on commercially important marine species including 10 fish, 6 crustacean, and 7 mollusk species. Since fry availability is a major constraint in the development of culture systems, a major research thrust of SEAFDEC AQD is the development of commercially viable technologies for breeding and seed production of commercially important marine fish and crustaceans such as milkfish, groupers, snappers and mud crabs, in addition to the production of fry and juveniles of endangered and depleted species such as the sea horse and the tropical abalone for stock enhancement and sea ranching. Although hatchery production of milkfish and sea bass are now commercially viable enterprises, research is being pursued to improve fry quality through feed supplementation and to lower production cost by using alternative live or artificial feeds. Larviculture techniques are being developed for technically demanding species such as groupers and snappers. The recent success in larviculture of the mud crab Scylla serrata is expected to stimulate the growth of the mud crab industry in the region. Similarly, encouraging developments in the breeding and larviculture of the sea horse and mollusks such as the tropical abalone will provide the necessary support to carry out future stock enhancement and sea ranching programs for these species.

Captive Lates calcarifer broodstock at Tigbauan, Iloilo (Philippines) were implanted with cholesterol-based pellets of the LHRH analogue D-Trp6-desGly10-LHRH ethylamide or D-hArg(Et2)6,Pro9-NHet-LHRH at doses between 9.0 and 23.5 μg/kg body weight. In May, one of ten LHRH-treated females released partially hydrated ova into the tank 4 days after implantation. In July, at least one (and probably four) of five LHRH-treated females spawned in the tank 2 days after implantation; 2.6 million hatchlings were collected. In August, both LHRH-treated females spawned in the tank 2 days after implantation; 978 000 hatchlings were collected. None of the sham-operated control fish spawned in any of the experiments. Captive Siganus guttatus broodstock implanted with silastic-based pellets of the LHRH analogue D-Nal (2)6 LHRH spawned 1–2 days earlier than sham-operated controls.

A collecting gear for naturally-spawned milkfish ( Chanos chanos Forsskal) eggs in circular floating net cages is described. The gear has been shown to be effective in collecting large numbers of eggs. The collecting gear can be adopted for other broodstock fish species held in circular floating net cages.

Natural spawnings of captive milkfish ( Chanos chanos Forsskal) held in floating cages were observed in 1980, 1981, 1983 and 1985. Frequency of spawnings increased from two in 1980 to 41 in 1985. Various collectors and collection methods were tried with only slight improvements in number of eggs collected. Although the number of eggs collected per spawning increased from 900 in 1980 to a maximum of 769 000 in 1985, the numbers were not sufficient for mass-scale fry production. The most urgent problem was egg predators inside the floating cages during the spawning season. This paper presents an improved method of egg collection using fine-mesh net cages (“hapa” nets, 1 mm mesh) which effectively prevented entry of egg predators. Before “hapa” nets were installed the number of eggs collected ranged from 3300 to 668 000. From 330 000 to 2 942 000 eggs were collected by using “hapa” net cages. With the new method mass-scale production of milkfish fry can be achieved.

Nine experiments were conducted to investigate the influence of chronic administration of testosterone (T) and gonadotropin-releasing hormone (GnRH) analogues on first maturation of 4- to 6-year-old fish and rematuration of 6- to over 9-year-old spent/regressed fish. Implantation of T or T in combination with luteinizing hormone-releasing hormone analogue (LHRH-A) had no marked effect on maturation rate of 4-year-old milkfish. The percentage of maturing fish was low and similar to controls in Experiment 1 (T, 31–35%; control, 35%) and Experiment 3 (T, 13%; T plus LHRH-A, 28%; control, 22.2%). Most of the 4-year-old maturing fish were males; maturing females were obtained only from the T-implanted groups in Experiment 1. In Experiment 3, T-implanted maturing females were able to retain yolky eggs whereas maturing control females did not, indicating that testosterone may have enhanced vitellogenesis and maintained the integrity of vitellogenic oocytes. Tank-reared maturing 4-year-old females, about half the size of older first maturing females, were induced to spawn. This is the first case of maturation and spawning of 4-year-old milkfish reared in tanks. As in Experiments 1 and 3, the percentage maturation of spent fish in Experiments 7 and 8 was similar for T-implanted and controls. On the other hand, the 4-year-old immature fish in Experiments 2 and 4, the 5- and 6-year-old immature fish in Experiments 5 and 6, and the spent 6-year-old fish in Experiment 9 were immature or regressed throughout. The factors which may have influenced the results of these experiments include age and reproductive history of the fish, timing of hormone implantation, experimental and holding conditions, and stress.

Milkfish ( Chanos chanos Forsskal) reared from wild-caught fry and from hatchery-bred fry matured at 3.5–5.5 years (2.3–4.9 kg). Maturation and spawning of the hatcherybred fish marks the first time the milkfish life-cycle has been completed in captivity. Milkfish at various stages of gonadal development were obtained in July–October 1980 and March–June 1981 derived from wild-caught fry, and in February–June 1983 from the hatchery-bred fish. The fish were held in floating net cages 9 m and 10 m diameter by 3 m deep, located in 7 m deep water off Igang, Guimaras Island, Philippines. Annual ranges of temperature and salinity were 25–33°C and 25–38 ppt, respectively. The fish were fed commercial feed pellet (42% protein) at 1.5–2% of body weight twice daily. Sexual maturation occurred during the natural breeding season of wild milkfish in the nearby waters. Gonadosomatic index (GSI) of mature males was 0.32–3.95 (wild-caught, 0.32–3.95; hatchery-bred, 1.71–3.85). For mature females it was 1.24–8.12 (wildcaught, 1.56–7.62; hatchery-bred, 1.24–8.12). Two spawnings were recorded in August 1980 and eight in May–July 1981 from the broodstock derived from wild-caught fry, with 342–6293 eggs collected from each spawning, while 14 spawnings were observed in May–June 1983 from the hatchery-bred fish, with 770–114 000 eggs collected. The time of spawning was between 23.00 and 02.00 h. Fertilization rate was 55–99% for the broodstock from wild-caught fry and 47–100% for the hatchery-bred fish. Hatch rate varied from 9 to 80%. Factors affecting spontaneous maturation, spawning and rematuration are discussed. Although slight improvements in egg collection were obtained, further innovations in egg collecting techniques will have to be developed. The results indicate the potential for hatchery production of milkfish fry from captive broodstock and for restocking of waters deprived of naturally occurring fry.

The response of maturing female milkfish to D-Ala6-des Gly10 mammalian GnRH ethylamide (mGnRH-A), D-Arg6-des Gly10 salmon GnRH ethylamide (sGnRH-A) and human chorionic gonadotropin (hCG) was investigated. The GnRH analogues and hCG were equally effective when administered by intramuscular injection at doses of 10 μg/kg and 100 μg GnRH-A/fish or 1000 IU hCG/fish. All of the females injected with HCG and 87.5% ( 7 8 ) of females injected with GnRH-A spawned. Pellet implantation of the GnRH analogues, however, was less effective based on 100 μg of pellet per fish, which provided from 20 to 36 μg of analogue per kg fish. Fish implanted with mGnRH-A or sGnRH-A showed responses which varied from oocyte hydration to spawning. Only 3 7 implanted with mGnRH-A and 1 7 implanted with sGnRH-A spawned; in the latter group, the average egg diameter was 11–17% smaller at the time of treatment compared with the other treated groups. Except for one, all fish with egg diameters above 0.65 mm had hydrated/ovulated oocytes or spawned. Females which spawned had egg diameters above 0.71 mm.

The response of mature female captive milkfish to mammalian and salmon gonadotropin-releasing hormone analogues (mGnRH-A and sGnRH-A) was investigated. Prior to spawning, six groups of three females received (1) 10–16 μg mGnRH-A from an osmotic pump implanted intraperitoneally (IP); (2) 100 μg mGnRH-A from a cholesterol/cellulose pellet implanted IP; (3) 10 μg/kg mGnRH-A as an intramuscular (IM) injection; (4) 10–16 μg sGnRH-A from an osmotic pump implanted IP; (5) 100 μg sGnRH-A from a cholesterol/cellulose pellet implanted IP, and (6) a cholesterol/cellulose pellet without analogue implanted IP. The most effective treatment was 100 μg sGnRH-A/fish given in a cholesterol/cellulose pellet; all ( 3 3 ) of the fish spawned. However, mGnRH-A was more effective ( 2 3 ) compared with sGnRH-A ( 1 3 ) if osmotic pumps were used to administer GnRH-A. If the dose and method of administration were not considered, then the salmon and mammalian GnRH analogues were equally effective (62–67%) for induction of ovulation and natural spawning in milkfish. Gonads of control fish regressed. At the doses tested, injections or pellet implantations were more effective compared with osmotic pumps. All pellet-implanted and injected females responded to treatment and 75% ( 6 8 ) spawned; half ( 3 6 ) of the pump-implanted females spawned. Spawning occurred from 18 to 36 h after treatment.