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This two-factor experiment incorporating three photoperiods (12L:12D, 16L:8D and 24L:0D) and two feeding methods (manual and self-feeding) was carried out to determine their effect on the growth performance of striped knifejaw, Oplegnathus fasciatus . Thirty juveniles were stocked into each 300 L tanks in triplicate for each treatment and fed a commercial diet for 10 weeks. Two-way ANOVA revealed that both photoperiod and feeding method have significant effect on the final mean weight, weight gain (%) and feed efficiency (FE) (P 0.05). Although the growth parameters didn't have significant difference between manual and self-feeding in fish exposed to 12L:12D photoperiod (P > 0.05), fish under other two photoperiods showed significant improvement under self-feeding system compared to manual feeding (P 0.05). Finally, the results suggested that the extended (16L:8D) and continuous (24 L:0D) photoperiods, and the provision of self-feeder could significantly improve the growth performance of striped knifejaw without changing the stress response. Statement of relevance This is the first report on the combined application of photoperiod manipulation and self-feeder on striped knifejaw, which revealed that the combination would help to improve the growth performance significantly. The indoor aquaculture industry, at least, will be benefited from the important insights achieved from this study to stimulate the growth performance of this commercially important species, which has great consumer demand in Japanese market.

Morphogenesis is most active during fish embryonic development with increased susceptibility to environmental stressors. In order to elucidate the causalities of malformations in fishes that produce buoyant eggs, this study estimated the time change of dissolved oxygen (DO) and carbon dioxide (DCD) concentrations in the interstitial water of red sea bream, Pagrus major, egg aggregation. Since direct measurement of DO and DCD concentrations is not possible by current methodologies, we measured those in one liter water containing approximately 500,000 eggs for their estimation. Calculated oxygen consumption and carbon dioxide excretion rates from observed data were 1.32 × 10− 6 and 2.16 × 10− 7 mg/ind/min, respectively. Volumetric method with these numeric values estimated that DO decreases below 10% saturation within 21 s and DCD increases to more than 135 mg/L within 60 min in the interstitial water of egg aggregation. These results suggest that hypoxia and hypercapnia may become teratogenic within a short time in the aquaculture practices of egg collection, treatment, and transportation where eggs aggregate at the water surface in containers or rearing tanks, or in the wild when eggs are exposed to red tide in the open sea.

We cloned the prolactin (PRL) and somatolactin (SL) genes of Pacific bluefin tuna (PBT: Thunnus orientalis) and investigated their daily mRNA expression patterns under aquacultured conditions. The PRL and SL cDNAs of PBT encode 211 and 231 aa prehormones which give rise to 187 and 207 aa mature peptides, respectively, and which belong to the same clades as those of other Perciformes. The highest gene expression levels of PRL and SL in PBT were found at 6 am under natural light conditions, which is about 3 times higher than the constitutive levels in both cases. Interestingly, scatter diagrams show a strictly correlated expression between PRL and SL (r = 0.82; p

The daily expression profile of growth hormone (GH) mRNA in juvenile Pacific bluefin tuna ( Thunnus orientalis ) was investigated under aquacultured conditions. Total RNA from pituitaries ( n = 5) was sampled from 10 am to 12 pm the next day at 1 h intervals. The expression levels of GH mRNA were evaluated using real-time PCR normalized against the β-actin gene. The expression level of GH transcripts reached a peak at 3–4 am at which time it was about 10 times higher than at any other time period. Considering their high growth rate compared to red seabream ( Pagrus major ) and other aquacultured species which shows continuous GH mRNA expression patterns, it can be concluded that the pulsed expression of GH mRNA just before daybreak is a key for the extremely high somatic growth rate of Pacific bluefin tuna.

The growth performance and stress response in striped knifejaw, Oplegnathus fasciatus (body weight 100–300 g) reared under four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) were investigated. Fish were fed a commercial diet to apparent satiation, two times a day for 8 weeks. A trial of acute handling and confinement stress was also carried out to investigate the stress-induced levels of different stress indicators in O. fasciatus . Blood was also collected from undisturbed fish which was considered as control. Although there were no significant differences in weight gain, specific growth rate (SGR) and feed conversion efficiency (FCE) in fish exposed to 6L:6D, 16L:8D and 24L:0D photoperiods, all parameters in these photoperiods were significantly higher than those of 12L:12D photoperiod ( P Acute stress significantly increased the plasma levels of cortisol (110.3 ng ml − 1 ) and glucose (195.4 mg dl − 1 ), and decreased plasma levels of total protein (0.8 g dl − 1 ); however, all parameters were returned back to the levels indistinguishable from those of control, undisturbed fish within 24 h. The levels of cortisol, glucose and total protein in fish exposed to different photoperiods during the study were far from the stress-induced levels ( P O. fasciatus reared from 100 to 300 g can be stimulated significantly by using the manipulated photoperiods where feeding time may be playing an important role to increase food intake and feed conversion efficiency. It also revealed that the artificial photoperiods did not cause significant stress response in fish.

Feeding enriched Artemia induces growth failure in Pacific bluefin tuna (PBT) Thunnus orientalis larvae; however, feeding of yolk-sac larvae of marine fish promotes larval growth. It is considered that this growth failure partly results from dietary docosahexaenoic acid (22:6n-3, DHA) deficiency. Therefore, we examined the effect of DHA contents in enriched Artemia on the growth of PBT larvae. Artemia nauplii were enriched with graded levels of DHA ethyl ester, and fed to PBT larvae for 9 days. Yolk-sac larvae of Japanese parrotfish Oplegnathus fasciatus were used as a reference diet. The DHA contents in Artemia increased with the enrichment from 0 mg g − 1 dry weight basis (DW) to 25 mg g − 1 DW, while the content in the reference diet was 21 mg g − 1 DW. Feeding of enriched Artemia significantly improved the growth of PBT larvae. However, this improvement was negligible when compared with the excellent growth of the larvae that were fed the reference diet. PBT larvae that were fed the reference diet accumulated approximately twice or much higher levels of DHA in the neutral and polar lipids in the body when compared with the larvae that were fed enriched Artemia . These results show that PBT larval growth cannot be promoted by feeding enriched Artemia even if the DHA contents in Artemia are elevated to the same levels as those of yolk-sac larvae. The incorporation of dietary DHA into phospholipids in the fish body may be desirable for the normal growth of PBT larvae.

Juvenile of red sea bream ( Pagrus major , body weight 1∼30 g) were reared under four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) with constant light intensity 1500 lx on the water surface to investigate their growth performance and stress response. Fish were fed a commercial diet to apparent satiation for 8 weeks of the experiment. Significantly higher weight gain and specific growth rates (SGR) were observed in fish exposed to a 24L:0D photoperiod followed by 16L:8D, 6L:6D and 12L:12D photoperiods ( P P

A number of primary and secondary features used as stress indicators in fish were investigated in red sea bream, Pagrus major exposed to different photoperiod regimes. In Experiment 1, fish weighing from 17 to 25 g were subjected to acute stress consisted of netting the fish from the rearing tanks and confinement in a small tank (30 L) half-full of water. The fish were then sampled at 0.5, 1, 4, 24, 48, and 72 h post-stress to investigate the stress-induced levels of different parameters. In Experiment 2, fish were exposed to different photoperiods (6L : 6D, 12L : 12D, 16L : 8D and 24L : 0D) for eight weeks. Blood samples were collected from the fish at the 1st, 4th and 8th week after exposure to the photoperiods. Acute stress significantly increased the plasma levels of cortisol (190.1 ng ml − 1 ) and glucose (109.5 mg dl − 1 ) and returned back to the basal levels within 24 h. In contrast, plasma levels of cholesterol (180.5 mg dl − 1 ), total protein (3.0 g dl − 1 ), potassium (4.1 mMol l − 1 ) and Ca ++ (11.3 mg dl − 1 ) were decreased significantly and returned to levels indistinguishable from those of control within 72 h except cholesterol, which did not recover within 72 h. In Experiment 2, fish exposed to 6L : 6D, 16L : 8D and 24L : 0D photoperiods had significantly higher cortisol levels than those exposed to the 12L : 12D photoperiod during the first week ( P P > 0.05). Fish exposed to the 24L : 0D photoperiod showed significantly higher weight gain and SGR followed by 16L : 8D, 6L : 6D and 12L : 12D photoperiods. The plasma levels of different stress indicators in different photoperiods in Experiment 2 were far lower than those of acute stress-induced levels observed in Experiment 1. On the other hand, no apparent signs of chronic stress were observed in fish exposed to different photoperiods. The results demonstrated that photoperiod manipulation caused no significant acute or chronic stress response in red sea bream.

Eggs of the Japanese eel, Anguilla japonica, were obtained by hormonally induced maturation and ovulation, and then categorized as buoyant and non-buoyant types in seawater after insemination. The water content of the buoyant eggs, 93.1%, was significantly higher than that of the non-buoyant eggs, 87.5%. Furthermore, the buoyant eggs had 1.5 times more free amino acids (FAA), 573.5 μmol/g dry weight (DW), than the non-buoyant eggs, 385.8 μmol/g DW, while no significant difference in egg lipid content or protein content was found. Compared to other pelagic eggs reported in the literature, the FAA content of the buoyant eggs was relatively low, although the water content was similar. These results suggest that there is a close relation between the quality of Japanese eel eggs obtained by typical hormonal inducement and the FAA content of the eggs, but the roles of FAA in the acquisition of egg buoyancy and fulfilling the early nutritional requirements are comparatively minor.

Red sea bream, Pagrus major, is one of the most important fish cultured in Japan. Two clones of red sea bream were produced. Eggs from a mitotic gynogenetic diploid (mitotic-G2N) red sea bream were inseminated either with sperm from a mitotic-G2N male to produce a heterozygous clone (hetero-clone), or with UV-irradiated sperm of Japanese parrot fish (Oplegnathus fasciatus) and the second meiotic division suppressed by cold shock to produce a homozygous clone (homo-clone). Normal diploids were also produced from one male and female as a control. The clonal status of the fish was confirmed by multilocus DNA fingerprinting. The fingerprinting patterns differed between individuals within the normal diploids. However, there was no variation between individuals within hetero- or homo-clones. The patterns of the homo-clones and the mother were identical, and all the bands of homo-clones were also observed in hetero-clones. Thus, the clonal status of homo- and hetero-clones was confirmed and the production of clones from the broodstock of mitotic-G2N was achieved. The hatching rates, survival rates and growth of the hetero- and homo-clones were recorded for a brief comparison with results of diploid controls.