The effects of salinity on the survival, growth and haemolymph osmolality of early juvenile blue swimmer crabs, Portunus pelagicus

The blue swimmer crab, Portunus pelagicus, is an emerging aquaculture species in the Indo-Pacific. Two experiments were performed to determine the effects of salinity on survival, growth and haemolymph osmolality of early juvenile P. pelagicus crabs. The salinities tested for the first experiment were 10, 15, 25 and 40 ppt, and for the second experiment 5, 20, 30, 35 and 45 ppt. Each salinity experiment was triplicated, with each replicate consisting of 10 stage 4 juveniles. Each experiment lasted 45 days. Mortalities and incidence of “molt death syndrome” were recorded daily, while the intermolt period, carapace length, carapace width and wet weight were measured at each molt. At the end of the experiments the haemolymph osmolality and dry weights were measured.

Results demonstrate that salinity significantly affects both the survival and growth of early P. pelagicus juveniles. Mortality was significantly higher (p < 0.01) for juveniles cultured at salinities ≤ 15 ppt and at 45 ppt. At a salinity of 5 ppt a complete mortality occurred on day 20. In all salinity treatments, the majority of mortalities were due to “molt death syndrome”. In experiment 1, immediate effects of salinity on growth and development were seen at 10 ppt as the intermolt period was significantly longer (p < 0.01) and the mean carapace size increase was significantly less (p < 0.01) at the first molt compared to the other treatments. Meanwhile, the specific growth rates (carapace length, width and wet weight) were significantly lower (p < 0.05) at high salinities (≥ 40 ppt) due to longer intermolt periods and significantly lower (p < 0.05) carapace size or wet weight increases.

The haemolymph osmolality exhibited a positive linear relationship with the culture medium with an isosmotic point of 1106 mOsm/kg, equal to a salinity of approximately 38 ppt. Based on the osmolality graph, high metabolic cost for osmoregulation due to increased hyper- and hypo-osmotic stress appeared to cause lower survival and specific growth rates of the crabs. The results demonstrate that a salinity range of 20–35 ppt is suitable for the culture of early juvenile P. pelagicus.     

Replacement of fish meal by meat and bone meal in diets for large yellow croaker, Pseudosciaena crocea

A growth experiment was conducted to investigate the effects of replacement of fish meal (FM) by meat and bone meal (MBM) in diets on the growth and body composition of large yellow croaker (Pseudosciaena crocea). Six isonitrogenous (43% crude protein) and isoenergetic (20 kJ g^− 1) diets replacing 0, 15, 30, 45, 60 and 75% FM protein by MBM protein were formulated. Each diet was randomly allocated to triplicate groups of fish in sea floating cages (1.0 × 1.0 × 1.5 m), and each cage was stocked with 180 fish (initial average weight of 1.88 ± 0.02 g). Fish were fed twice daily (05:00 and 17:30) to apparent satiation for 8 weeks. The water temperature ranged from 26.5 to 32.5 °C, salinity from 32 to 36‰, and dissolved oxygen content was approximately 7 mg l^− 1 during the experimental period. Survival decreased with increasing dietary MBM and the survival in the fish fed the diet with 75% protein from MBM was significantly lower than other groups (P < 0.05). There were no significant differences in specific growth rate (SGR) among the fish fed the diets with 0 (the control group), 15, 30 and 45% protein from MBM. However, SGR in the fish fed the diets with 60 and 75% protein from MBM were significantly lower than other groups (P < 0.05). No significant differences in feeding rate were observed among dietary treatments. The digestibility experiment showed that the apparent digestibility coefficients (ADC) of dry matter, protein, lipid and energy of MBM were significantly lower compared with those of FM (P < 0.05). Essential amino acid index was found to be correlated positively with SGR in the present study, suggesting that essential amino acid balance was important. Body composition analysis showed that the carcass protein and essential amino acids were not significantly affected by dietary MBM. The lipid and n-3 highly unsaturated fatty acid (n-3 HUFA) in fish muscle, however, significantly decreased with increasing dietary MBM. These results showed that 45% of FM protein could be replaced by MBM protein in diets of large yellow croaker without significantly reducing growth. It was suggested that the reduced growth with higher MBM was due to lower digestibility and imbalance of essential amino acids.     

Substitution of Chaetoceros muelleri by Spirulina platensis meal in diets for Litopenaeus schmitti larvae

The nutritional response of Litopenaeus schmitti larvae to substitution of Chaetoceros muelleri by Spirulina platensis meal (SPM) was evaluated. The substitution levels (S) were 0%, 25%, 50%, 75% and 100%, dry weight basis. Final larval length (FL) ranged from 1.98 to 3.16 mm for the different substitution levels. There was a significant relationship between S and FL, described by the following quadratic equation: FL = 2.853 + 0.01598S − 0.000233S². The substitution level (S) yielding maximum FL was 34.2%. Development index (DI) values ranged from 2.84 to 3.93 and were dependent on substitution level. The corresponding equation was DI = 3.799 + 0.00945S − 0.000189S² (P < 0.01). Maximum DI was obtained at 25.0% substitution. Survival was high (82–87%) and no significant differences were found between treatments. Protein digestibility of either microalgae was high, with 92% for SPM and 94% for C. muelleri, with no significant differences between them. The results in this study indicate that an adequate balance of nutrients in relation to the requirements of the species is critical. To simultaneously improve FL and DI, a 30% substitution of C. muelleri by SPM is suggested. This is equivalent to feeding 0.15 mg larvae^− 1 day^− 1 dry weight basis of a 70% C. muelleri/30% SPM diet, representing 0.078 mg protein larvae^− 1 day^− 1, 0.026 mg lipids larvae^− 1 day^− 1 and 2.732 J larvae^− 1 day^− 1.     

Effect of hyperoxygenation and low water flow on the primary stress response and susceptibility of Atlantic salmon Salmo salar L. to experimental challenge with IPN virus

Intensive salmon smolt production normally includes reduced water flow and hyperoxygenation (added oxygen) of remaining water. There is little information on how different water quality parameters influence the fish health and the susceptibility to infectious diseases. The current experiment was carried out to evaluate if the combination of hyperoxygenation and reduced water flow (hyperoxic) can act as a chronic stressor to salmon in freshwater (FW) in such a way that it increases the susceptibility to IPN virus (IPNV) following seawater transfer. In FW, after 22 days of hyperoxic exposure plasma ion, TBARS and cortisol were measured. The cortisol levels were significantly (p = 0.011) higher in the hyperoxic group compared to controls maintained under normal oxygen saturation and water flow (normoxic), indicating chronic stress. Hyperoxygenation in FW caused decreased plasma [Cl⁻] compared to the normoxic group (p = 0.037), while [K⁺] tended to be higher in the hyperoxic group (p = 0.088). No significant differences were observed in plasma [Na⁺], total osmolality, TBARS or hematocrit, but there was a tendency towards a lower hct in the hyperoxic compared to the normoxic group. In SW the mortality was higher in the hyperoxic group challenged with IPNV (34%) compared to the normoxic group challenged with IPNV (20%) (p = 0.02), and no mortality was observed in the PBS injected fish. The challenged fish showed an overall increase in plasma cortisol day 8, 10, 12 and 14 post-challenge (p = 0.015, p = 0.000, p = 0.046 and p = 0.022 respectively). After SW transfer and challenge, plasma [K⁺] was elevated in both challenged groups, but no consistent trends were found for plasma [Cl⁻], [Na⁺] or total osmolality during the SW phase. There were no significant differences in the gene expression level of IFN 1, Mx and IL 1β prior to challenge, suggesting that the basic expression level of these genes were not affected by hyperoxygenation. IPNV was detected in kidney and pylorus, by immunohistochemistry, cell culture, and RT-PCR in head kidney. This experiment indicates that chronic stress induced by a combination of low water flow and hyperoxygenation increases the susceptibility to IPNV challenge.     

Effects of temperature and lipid droplet adherence on mortality of hatchery-reared southern hake Merluccius australis larvae

Effects of exogenous (water temperature) and endogenous (lipid droplet adherence) factors were experimentally tested on early survival of southern hake Merluccius australis reared under controlled conditions. Experiments to determine the effect of temperature (10, 12 and 14 °C) on larval growth rates and yolk-sac absorption rates of unfed southern hake were carried out under laboratory conditions. There was no significant differences in growth rates at the temperature range tested (ANCOVA, F = 0.164, p > 0.25), but yolk-sac absorption rates and mortality increased with temperature (ANCOVA, F = 53.84, p < 0.001). A high percentage (between 31 and 81%) of hake eggs showed a lipid droplet not adhered (i.e., freely moving in the yolk, and not located in the posteriormost portion of the yolk-sac). In a second experiment, fed southern hake larvae with the lipid droplet not adhered during embryonic development did not survive after yolk-sac absorption. This study provides the first data on the influence of the lipid droplet absorption on larval survival of cultured hake, and can be used as an early indication of the quality of the batch.     

Efficacy, tissue distribution, and residue depletion of oxytetracycline in WS-RLP infected California red abalone Haliotis rufescens

Oxytetracycline (OTC) was recently demonstrated to be an effective therapeutant for California red abalone (Haliotis rufescens) infected with the agent of withering syndrome (WS), a Rickettsia-like prokaryote (WS-RLP). This study examined the influence of temperature on the efficacy and pharmacokinetics of oral OTC treatments on WS-RLP infected red abalone, H. rufescens. Medication was administered in an artificial diet containing 1.85% active OTC at a rate of 103.4 mg/kg abalone for 10, 20 and 30 days at both 13.4 °C and 17.3 °C. Drug residue concentrations, WS-RLP burden and WS-associated pathological changes within foot muscle and digestive gland were measured 3, 17, 23, 42, 63, 81, 102, 122, and 160 days after OTC treatment. In all samples the highest concentrations of OTC were detected on the first sample day. Furthermore, all sampling periods showed significantly less OTC in foot muscle samples relative to corresponding digestive gland samples (p < 0.001). While drug depuration occurred rapidly from foot muscle, unusually high concentrations and long depuration times were measured within the digestive gland. The pharmacokinetic trends in both the foot muscle and digestive gland at 13.4 °C were adequately described by a one-compartment model, while the digestive gland depuration models within the 17.3 °C treatments conformed to a two-compartment model. At both temperatures treatment duration gave rise to significant differences in OTC accumulation and depletion (p < 0.001). Despite this, terminal elimination rate constants were similar. Estimated half-lives were similar among all treatments for digestive gland (23.8–27.5 d) and all treatments for the foot muscle at 13.4 °C (10.7–13.4 d; calculated only for the 13.4 °C treatments). At both temperatures all three durations of drug treatment led to significant reductions in WS-RLP prevalence, foot muscle atrophy, and mortality. WS-RLP re-challenge trials initiated 44, 88, and 122 days following the 10-day treatment at 17.3 °C showed reduced susceptibility to re-infection for up to 88 days after treatment, suggesting that digestive gland OTC residues confer long-term resistance to pathogen. Atomic absorption spectroscopy conducted on both foot muscle and digestive gland found significantly higher concentrations of iron, zinc, and manganese in the digestive gland, offering an explanation behind the underlying mechanism of OTC retention for extended periods within this tissue.     

Diurnal variation of tryptic activity in larval stage and development of proteolytic enzyme activities of malabar grouper (Epinephelus malabaricus) after hatching

Diurnal variation in tryptic activity and developmental changes in proteolytic enzyme activities of malabar grouper larvae (Epinephelus malabaricus) were examined. Five different groups were prepared for the experiment of diurnal variation of tryptic activity in larvae: larvae were fed Thai-type rotifers Brachionus rotundiformis from the time of mouth opening, fed rotifers from 6 h after mouth opening, 12 h, 24 h and not fed rotifers (starved control). The experimental tanks were placed in temperature-controlled baths at 28 °C under 24 h light. Developmental changes in proteolytic activity of trypsin and pepsin-like enzyme were measured from hatching to 57 days after hatching (DAH).

The tryptic activity of all fed groups showed the same pattern, and the diurnal variation of tryptic activity was clearly observed from 3 to 6 DAH. The highest tryptic activities were found at 19:00, and the activities were lowest from 01:00 to 07:00. In contrast, that of non-fed larvae was low compared to the fed groups, however the diurnal variation of tryptic activity was shown same tendency to the fed groups. Interestingly, both groups (fed and non-fed) were exhibited a circadian rhythm under the 24 h light conditions and delaying of first-feeding. Tryptic activity of larvae notably increased from 40 to 45 DAH and markedly decreased at 52 DAH. In contrast to the tryptic activity, that of pepsin-like enzyme clearly increased from 47 to 51 DAH. The results suggest that a functional change of protein digestion occurs from 40 to 50 DAH related with metamorphosis in malabar grouper. These results could contribute to determining appropriate feeding schedules, such as feeding time, frequency and optimal time to change food items, in mass-scale production of the present species.     

Optimal dietary protein requirement for juvenile ivory shell, Babylonia areolate

A growth experiment was conducted to determine the optimal dietary protein requirement for juvenile ivory shell reared in indoor aerated aquaria. Six isoenergetic experimental diets using fish meal, casein and gelatin as protein sources were formulated to contain graded levels of protein (27, 33, 38, 43, 49 and 54% of dry diet, respectively). Triplicate groups of 40 shells (average weight 93.50 ± 1.70 mg) were stocked in 120-l tanks and fed to apparent satiation twice daily for 8 weeks. The results showed that the growth performance and feed utilization were significantly affected by dietary protein level (P < 0.05). Maximum weight gain, mean protein gain, specific growth rate and soft body to shell ratio occurred at 43% dietary protein level (P < 0.05). There were significant differences in protein, lipid, moisture and ash content in soft body; except that ash content in shell was not significantly affected by dietary protein level. Pepsin activity in soft body tissue significantly increased with dietary protein level up to 43%, and trypsin-like enzyme activity increased with dietary protein level up to 49%. However, lipase activity in soft body decreased with increasing dietary protein level. However, no significant differences (P < 0.05) in survival, calcium, phosphorus concentration in the shell and soft body were found among dietary treatments. Quadratic regression analysis of weight gain against dietary protein level indicated that the optimal dietary protein requirement for maximum growth and feed utilization of juvenile ivory shell is 45% of dry diet.     

Effect of probiotics, Enteroccus faecium, on tilapia (Oreochromis niloticus) growth performance and immune response

The aim of this study was to analyze the effect of a probiotic bacterium, Enterococcus faecium ZJ4 on growth performances and immune responses of tilapia (Oreochromis niloticus). The tilapias were treated with E. faecium ZJ4 at a final concentration of 1 × 10⁷ cfu ml^− 1 in aquaria water every 4 days. Six aquaria with three replicates for treated and controls were used. After 40 days, the tilapias supplemented with the probiotic showed significantly better final weight and daily weight gain (DWG) than those fed the basal diet (Control) (P < 0.05). There was no remarkable difference (P > 0.05) in the total serum protein, albumin content, globulin concentration and A/G ratio between the treated and control tilapias. The result of lysozyme activity assay was similar to these biochemical indexes. However, the complement component 3 content, myeloperoxidase (MPO) activity and the respiratory burst activity of blood phagocytes were higher (P < 0.05) in E. faecium treated tilapias (trial 1) than the controls.     

Comparative performance of Gamma Amino Butyric Acid (GABA) and 5-Hydroxytryptamine (5-HT) in the diet of larvae and post larvae of giant freshwater prawn, Macrobrachium rosenbergii: Effect of dose and route of administration on growth and survival

Three experiments were conducted to evaluate the effect of different dose and route of administration of 5-Hydroxytryptamine (5-HT) and Gamma Amino Butyric Acid (GABA) on growth, survival and pigmentation of giant freshwater prawn, Macrobrachium rosenbergii, larvae (experiment 1) and post larvae (experiment 2 and 3). In experiment 1 larva were stocked at 100 /L in seven different treatments with each of three replicates. The treatments were T1 (control), T2 (100 μg/ml of 5-HT bath exposure for 2 days), T3 (1 μM of GABA bath exposure for 2 days), T4 (0.5% 5-HT in feed), T5 (0.25% 5-HT in feed), T6 (0.5% GABA in feed) and T7 (0.25% GABA in feed). Highest growth, transformation rate, pigmentation and survival of larvae were recorded in T2 group in experiment 1. In experiment 2, post larvae were stocked at 70 per tank with 200 L of water for 45 days. This experiment consisted of 5 treatment groups with each of 3 replication viz. T1 (control), T2 (0.5% 5-HT in feed), T3 (0.25% 5-HT in feed), T4 (0.5% GABA in feed) and T5 (0.25% GABA in feed). At the end of this experiment growth was found to be higher in the control than the other treatment group showing inhibitory effect of 5-HT and GABA on growth of post larvae. To confirm the result, a third experiment was conducted for 30 days. Thirty numbers of post larvae having similar size were segregated from the previous experimental tanks (experiment 2) and stocked in the tanks of 100 L of water for experiment 3. All treatments were fed with control diet. There was similar growth pattern in all the treatments, which were higher (P < 0.05) than control, confirms the inhibitory effect of neurotransmitter in the diet of PL. Therefore, the overall results of the present study suggest that the bath treatment of neurotransmitter is superior to the dietary addition with regard to the growth, survival and pigmentation of M. rosenbergii larvae. 5-HT is more effective than the GABA for larvae of M. rosenbergii.     

Involvement of trypsin and chymotrypsin activities in Atlantic cod (Gadus morhua) embryogenesis

Proteases play a key role in yolk formation and degradation during embryogenesis of marine fish. This study presents the first clear data on the involvement of trypsin and chymotrypsin activities in the embryogenesis of Atlantic cod (Gadus morhua). Both enzyme activities were shown to be present in unfertilized eggs followed by a significant decline (P < 0.01) in trypsin activity during the first 4 days post fertilization (dpf). Thereafter, the trypsin- and chymotrypsin activities increased to a maximum around day 9 pf. A decline in trypsin and chymotrypsin activities was observed from day 10 pf with minimal activity just prior to first feeding (day 15 pf). Western blot analysis, using polyclonal antibodies raised to Atlantic cod trypsins I and Y, mostly coincided with the trypsin activity profile. The novel trypsin Y was previously shown to have both trypsin- and chymotrypsin-like activities. Thus, some of the chymotrypsin activity observed in the samples may be originated from trypsin Y. The low trypsin and chymotrypsin activities just prior to first feeding (13–15 dpf) may indicate insufficient digestive function as trypsin has been shown to be a suitable short-term indicator reflecting the nutritional quality of marine fish larvae.     

Breeding and juvenile culture of the lined seahorse, Hippocampus erectus Perry, 1810

All seahorse species worldwide have been placed under CITES Appendix II since 2004, because they have been over-exploited for traditional Chinese medicine and aquarium trades. Aquaculture has been recognized as a long-term solution for sustaining the seahorse trade while minimizing wild collection. In this study, we evaluated the breeding and juvenile culture of an important aquarium seahorse species, the lined seahorse Hippocampus erectus, Perry 1810. Pairing, mating and copulation behavior were observed. Gestation time and brood size were 17.33 ± 2.94 days and 272.33 ± 66.45 individuals/brood, respectively. Growth rates differed among juveniles from different broods. Effects of temperature on the growth rates and survivorship of the juveniles during the first two weeks were compared. The highest growth rate and survivorship of the juveniles occurred at 28–29 °C among the temperatures tested (24–33 °C). Growth rate and survivorship of the juveniles during the first 9 weeks at 28 °C were investigated. The final standard length and survivorship of the juveniles were 6.32 ± 0.52 cm and 71.11 ± 10.18%, respectively, and the relationship between the wet weight and the standard length of the juvenile seahorses can be expressed as: W = 0.0034 L^2.5535 (r² = 0.9903, n = 12, P < 0.01). These findings suggest that H. erectus is a good candidate for commercial aquaculture.     

Effects of Cu-exchanged montmorillonite on growth performance, microbial ecology and intestinal morphology of Nile tilapia (Oreochromis niloticus)

A total of 360 Nile tilapia at an average initial body weight of 3.9 g were randomly allocated to 4 treatments, each of which had three replicates of 30 fish/tank and used to investigate the effects of Cu²⁺-exchanged montmorillonite (Cu-MMT) on growth performance, microbial ecology of the skin, gill and intestine, and intestinal morphology. The dietary treatments were: 1) basal diet, 2) basal diet + 1.5 g/kg MMT, 3) basal diet + 30 mg/kg copper as CuSO₄ (equivalent to the copper in the Cu-MMT treatment group), or 4) basal diet + 1.5 g/kg Cu-MMT. The results showed that supplementation with Cu-MMT significantly improved growth performance as compared to control and fish fed with Cu-MMT had higher growth performance than those fed with MMT or CuSO₄. Supplementation with Cu-MMT reduced (P < 0.05) the total intestinal aerobic bacterial counts and affected the composition of intestinal microflora with a tendency of Aeromonas, Vibrio, Pseudomonas, Flavobacterium, Acinetobacter, Alcaligence, Enterobacteriaceae decreasing as compared with control. Measurements of villus and microvillus heights at different sites of the intestinal mucosa indicated that dietary addition of MMT or Cu-MMT improved intestinal mucosal morphology. However, the microbial ecology of the skin and gill was not affected by the addition of CuSO₄, MMT or Cu-MMT. Supplementation with CuSO₄ had no (P > 0.05) effect on the growth performance, microbial ecology and intestinal morphology. The results showed that Cu-MMT exhibited antibacterial activity in vivo and protected intestinal mucosa from invasion of pathogenic bacterium and toxins, resulting in a positive effect on the growth performance.     

Hemagglutinating activity and electrophoretic pattern of hemolymph serum proteins of Penaeus monodon and Macrobrachium rosenbergii to white spot syndrome virus injections

The giant fresh water prawn Macrobrachium rosenbergii is known to be highly tolerant to white spot syndrome virus (WSSV) infections when compared to the widely cultured marine tiger shrimp Penaeus monodon. At present, the exact mechanism of tolerance by M. rosenbergii to WSSV is not known. In this study, we attempt to study the effect of WSSV injections on the hemagglutination activity of the hemolymph serum of both P. monodon and M. rosenbergii and look for changes if any, on their hemolymph serum protein electrophoretic patterns. Our results show that M. rosenbergii had significantly (p < 0.05) higher hemagglutinating activity against mouse erythrocytes when compared to P. monodon. As the infection progressed to 48 h there was a further increase (p < 0.05) in the hemagglutination activity in M. rosenbergii, while it decreased in P. monodon. 12% SDS-PAGE analysis of the hemolymph serum of M. rosenbergii infected with WSSV did not show any new protein bands, whereas few bands with decreased intensity was observed in moribund P. monodon where the hemagglutinating activity was also observed to be decreased. The results indicate that hemolymph hemagglutinin levels are modulated in crustaceans as a response to viral infections.     

Age, growth, and reproduction of silky sharks, Carcharhinus falciformis, in northeastern Taiwan waters

To examine the age, growth and reproduction of silky sharks, Carcharhinus falciformis, in the waters off northeastern Taiwan, 469 specimens (213 females and 256 males) were collected from August 2000 to January 2002 at the Nanfanao fish market, northeastern Taiwan. The relationship between body weight (W) and total length (TL) for both sexes combined was expressed as: W = 2.92 × 10⁻⁶ TL^3.15 (n = 469, p < 0.01). The relationship between TL and vertebral centrum radius (R) for both sexes combined data was estimated as: TL = 25.979 + 18.197R (n = 250, p < 0.01). Growth bands (including translucent and opaque zones) in precaudal vertebrae formed once a year between December and January and were counted up to 11 and 14 for females and males, respectively. The von Bertalanffy growth function (VBGF) was used to model the observed length at age data. The sexes combined VBGF predicted an asymptotic length (L_∞) = 332.0 cm TL, growth coefficient (k) = 0.0838 year⁻¹, age at zero length (t₀) = −2.761 year (n = 250, p < 0.01). Size at 50% maturity for males was estimated to be 212.5 cm based on the logistic curve, which corresponded to 9.3 years. Females matured at 210–220 cm, which correspond to 9.2–10.2 years. The length at birth was estimated to be 63.5–75.5 cm TL. The number of embryos per litter was 8–10 and sex ratio of embryos was 1:1.     

Influence of light intensity on feeding, growth, and early survival of leopard coral grouper (Plectropomus leopardus) larvae under mass-scale rearing conditions

This study investigated the effect of different light intensities on feeding, growth and survival of early stage leopard coral grouper Plectropomus leopardus larvae. Four different light intensities (0, 500, 1000 and 3000 lx) were used and larvae were kept under constant light conditions from 0 day after hatching (DAH) to 5 DAH. The larvae were fed a small S-type of Thai strain rotifers at a density of 20 individuals/mL from 2 DAH. The number of rotifers in larval digestive organ and total length of larvae were examined at 3 h intervals between 04:00 and 22:00 h on 3 DAH, and thereafter at 6 h intervals until the end of the experiment (5 DAH). Four experimental trials of the larval rearing were repeated using by 60 kL mass-scale rearing tanks. The results indicate that coral grouper larvae are visual feeders and their food intake increases with increasing light intensity. Food intake of larvae reared at 3000 lx was significantly higher than those reared at 0–1000 lx on 3 DAH despite being the first-feeding day (P < 0.01). On 4 DAH, total length of larvae reared at 3000 lx was significantly larger than those reared at the lower light intensities (0, 500 and 1000 lx), and thereafter light intensity significantly influenced larval feeding and growth until the end of the experiment. Survival on 5 DAH did not show a significant difference between light intensities, but survival rate at 3000 lx and 1000 lx had a tendency to be higher than those reared at the lower light intensities (0 and 500 lx). In contrast, larvae reared at 0 lx exhibited stagnant and/or negative growth. These results indicate that light intensity is significantly the factor affecting larval feeding, growth, and survival in coral grouper larvae under the rearing conditions.     

Effect of dietary taurine enhancement on growth and development in red sea bream Pagrus major larvae

This study investigated the effect of feedings taurine‐enriched rotifers on the growth and development of larval red sea bream (RSB). Rotifers incubated in taurine‐enriched water at a taurine concentration of 800 mg L^?1 (T‐800) and 0 mg L^?1 (T‐0) were fed to larvae from 3 to 20 days after hatching (DAH). Notochord length, body weight and specific growth rate of T‐800 group were significantly greater than those of T‐0 at 14, 17, 9–11 and 18–20 DAH. Taurine content of larvae in the T‐800 group increased rapidly from 11 DAH and thereafter remained significantly higher than T‐0. Flexion larvae firstly appeared in both groups at 8 DAH, however, at 20 DAH post‐flexion larvae were significantly more abundant in T‐800 than T‐0. While nucleic acid and protein contents (μg mg^?1 wet fish) showed remarkable changes, ontogenetic growth in RSB larvae stage was observed to switch from hyperplastic growth to hypertrophic growth with the start of the flexion stage. Although a similar change in nucleic acid contents was observed between the two groups, the protein content (μg fish^?1) and protein/DNA ratio of T‐800 remained higher than that of T‐0 during the hypertrophic growth period. These results suggest that dietary taurine accelerates the growth and development in RSB larvae especially during hypertrophic growth (flexion stage) after the early hyperplastic growth.     

Ontogeny of the digestive tract in shi drum (Umbrina cirrosa L.) reared using the mesocosm larval rearing system

Histological changes of the digestive tract were studied in shi drum (Umbrina cirrosa) from hatching until 41 days post hatching (dph), when the fry had a mean (±S.D.) total length (TL) of 32 ± 2 mm and wet weight (WW) of 0.42 ± 0.07 g. Larvae were reared using the mesocosm technique, the most natural among commercially employed rearing methods for marine larvae. Shi drum opened their mouth at 2 dph (2.78 ± 0.09 mm TL), at which time 90% of the larvae already had an inflated swim bladder. The differentiation of the digestive tract into buccopharynx, esophagus, and anterior and posterior intestine was completed by 3 dph (2.82 ± 0.07 mm TL), 1 day after the onset of exogenous feeding. The alimentary canal started coiling and formed its first loop at 2 dph, while the pancreas and liver were differentiated at 3 dph. Yolk sac reserves lasted until 7 dph (4.3 ± 0.1 mm TL), suggesting a brief period of endogenous and exogenous feeding. The first esophageal goblet cells appeared at 7 dph containing acid mucins and at 8 dph taste buds appeared on the buccopharyngeal epithelium. The stomach was morphologically differentiated at 9 dph (5.5 ± 0.1 mm TL) when gastric glands became abundant in the cardiac region, and the first pyloric caeca appeared at 14 dph (10.1 ± 0.9 mm TL). Supranuclear eosinophilic vacuoles were observed in the posterior intestine between 3 and 11 dph (6.3 ± 0.9 mm TL). Their number decreased as the stomach differentiated, suggesting a change in the protein digestion mechanism. The results of the study suggest a rapid development of shi drum and its digestive system and underline the possibility of weaning larvae to artificial feed even earlier than the 12 dph employed in the present study.     

Photoperiod influences the growth, food intake, feed efficiency and digestibility of red sea bream (Pagrus major)

Two consecutive trials were conducted to investigate the effects of photoperiod manipulation on growth rate, food intake and feed conversion efficiency (Trial 1), and the digestibility of nutrients and energy (Trial 2) in red sea bream, Pagrus major (body weight 19–120 g). Fish were exposed to four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) with light intensity 1500 lx on the water surface. The fish were fed with a commercial diet to apparent satiation. In Trial 2, 0.5% chromic oxide (Cr₂O₃) was used as an inert marker. Significantly higher weight gain and specific growth rates were observed in fish exposed to a 24L:0D photoperiod followed by 16L:8D, 6L:6D and 12L:12D photoperiods (P < 0.05). Food intake and feed conversion efficiency (FCE) were also significantly higher in fish exposed to 24L:0D followed by 16L:8D, 6L:6D and 12L:12D photoperiods (P < 0.05). Fish exposed to 24L:0D and 16L:8D photoperiods showed significantly higher lipid and energy digestibility than those exposed to a 12L:12D photoperiod (P < 0.05). The results demonstrated that the enhancement of growth performances under 16L:8D and 24L:0D photoperiods were attributed to improved appetite, greater food intake and higher feed conversion efficiency as well as higher digestibility.     

Metabolic scope, swimming performance and the effects of hypoxia in the mulloway, Argyrosomus japonicus (Pisces: Sciaenidae)

The culture of the mulloway (Argyrosomus japonicus), like many other Sciaenidae fishes, is rapidly growing. However there is no information on their metabolic physiology. In this study, the effects of various hypoxia levels on the swimming performance and metabolic scope of juvenile mulloway (0.34 ± 0.01 kg, mean ± SE, n = 30) was investigated (water temperature = 22 °C). In normoxic conditions (dissolved oxygen = 6.85 mg l^− 1), mulloway oxygen consumption rate (M·o₂) increased exponentially with swimming speed to a maximum velocity (U_crit) of 1.7 ± < 0.1 body lengths s^− 1 (BL s^− 1) (n = 6). Mulloway standard metabolic rate (SMR) was typical for non-tuna fishes (73 ± 8 mg kg^− 1 h^− 1) and they had a moderate scope for aerobic metabolism (5 times the SMR). Mulloway minimum gross cost of transport (GCOT_min, 0.14 ± 0.01 mg kg^− 1 m^− 1) and optimum swimming velocity (U_opt, 1.3 ± 0.2 BL s^− 1) were comparable to many other body and caudal fin swimming fish species. Energy expenditure was minimum when swimming between 0.3 and 0.5 BL s^− 1. The critical dissolved oxygen level was 1.80 mg l^− 1 for mulloway swimming at 0.9 BL s^− 1. This reveals that mulloway are well adapted to hypoxia, which is probably adaptive from their natural early life history within estuaries. In all levels of hypoxia (75% saturation = 5.23, 50% = 3.64, and 25% = 1 .86 mg l^− 1), M·o₂ increased linearly with swimming speed and active metabolic rate (AMR) was reduced (218 ± 17, 202 ± 14 and 175 ± 10 mg kg^− 1 h^− 1 for 75%, 50% and 25% saturation respectively). However, U_crit was only reduced at 50% and 25% saturation (1.4 ± < 0.1 and 1.4 ± < 0.1 BL s^− 1 respectively). This demonstrates that although the metabolic capacity of mulloway is reduced in mild hypoxia (75% saturation) they are able to compensate to maintain swimming performance. GCOT_min (0.09 ± 0.01 mg kg^− 1 m^− 1) and U_opt (0.8 ± 0.1 BL s^− 1) were significantly reduced at 25% dissolved oxygen saturation. As mulloway metabolic scope was significantly reduced at all hypoxia levels, it suggests that even mild hypoxia may reduce growth productivity.