Impacts of short-term salinity and turbidity stress on the embryonic stage of red sea bream Pagrus major

Fisheries Science - Heavy rainfall can reduce salinity and increase turbidity in coastal waters, creating stressful conditions for the organisms found there, especially for the early stages of...     

Gonadal sex differentiation and sex control in red sea bream, Pagrus major

The gonadal sex differentiation in red sea bream, Pagrus major, which is one of the most important species for aquaculture in Japan, was revealed histologically. The suitable conditions for induction of all-male groups in the fish were investigated, and functional males were induced by the conditions of oral administration of 17α-methyltestosterone. The sex determination of this fish was also discussed.     

Acoustic pressure sensitivities and effects of particle motion in red sea bream Pagrus major

The auditory pressure thresholds of red sea bream were examined using cardiac response in the field by placing fish subjects far from the sound source to prevent particle motion. Pressure and particle motion thresholds were also obtained using the auditory brainstem response (ABR) technique. The thresholds at 100 and 200 Hz were significantly higher when measured using the cardiac response in the far field than those obtained in previously conducted experiments in experimental tub. However, thresholds obtained using ABR from 200 to 500 Hz were not remarkably lower, although significantly different (0.01 < P < 0.05), compared with those obtained using cardiac response in the far field. Furthermore, calculated particle velocity thresholds indicated that fish probably detected particle motion within the frequency range of 50–200 Hz, even in fish with a deactivated lateral line. Although the ABR method is widely applied in fish auditory study, hearing thresholds are apparently affected by particle motion.     

Optimum dietary taurine level in casein-based diet for juvenile red sea bream Pagrus major

ABSTRACT:   This study was conducted to investigate the effect of dietary taurine and cholyltaurine (C-tau) on growth and body composition of juvenile red sea bream Pagrus major . Semi-purified casein-based diets supplemented with 0 (control diet), 0.1, 0.3, 0.5 and 0.7% taurine and 0.5% C-tau were fed to red sea bream (average body weight 4.7 g) for 6 weeks at 20°C. The growth and feed efficiency were the lowest in fish fed the control diet. Taurine supplementation improved the growth and feed efficiency of fish dose-dependently, and the taurine requirement was estimated as 0.52% in terms of optimizing growth and 0.48% in terms of optimizing feed efficiency. Taurine content in the whole body and liver increased with the dietary taurine level. Supplemental C-tau at the 0.5% level had limited effects on the growth and no effect on body taurine, biliary bile salt and liver fat contents. From these results it can be inferred that the optimal dietary taurine requirement of juvenile red sea bream is 0.5% on a dry weight basis, and that the supplementation of taurine in the diet not only improves the growth but also increases hepatic lipid levels of red sea bream juveniles.     

Vertebral deformities in cultured red sea bream, Pagrus major, Temminck and Schlegel

Vertebral deformities were investigated in cultured red sea bream, Pagrus major. In the field, deformities in seedlings were categorized and their incidence was calculated. In the laboratory, the symptoms of major vertebral deformities were examined morphologically using radiographs and by making transparent skeletal specimens. The internal structure of deformed vertebrae was examined histologically. The shortened body condition had the highest incidence (0.9–8.3%) of all deformities in the seedlings. In individuals with the shortened body condition, the ratio of trunk and caudal part length to body height was smaller. These fish had skeletal anomalies in the vertebrae, mainly centrum defects (64.3%) or undersized centrums (25.2%). The specimens with centrum defects had a characteristic anomaly in the vertebrae, with plural pairs of neural and haemal spines on a single centrum. This anomaly was frequently observed in the posterior abdominal vertebrae. The internal skeletal structure of such abnormal centrums was basically the same as that of normal centrums. In all the specimens with undersized centrums, both the centrum length and diameter were shorter than normal except for the first and second centrum, and urostyle.     

The microhabitat and size of gammarid species selectively predated by young red sea bream Pagrus major

SUMMARY: Mechanisms of prey selection by young red sea bream Pagrus major were examined in Shijiki Bay by comparing the species composition of gammaridean amphipods in the diet with that in the environment. Although gammarids were the major source of food for young red sea bream, their species composition in fish stomachs changed with the growth of fish from June to October and always differed from that in the environment. The patterns of selection of gammarids were related most closely to the microhabitat of each species before mid-July. The order of selectivity of species in terms of the microhabitat was as follows: epifaunal species > shallow-burrowing species > infaunal tube-dwelling species > deep-burrowing species. After mid-July, however, selection was determined by the body size of gammarid species. Byblis japonicus that were large enough as a prey species were mainly consumed and other smaller species were not selectively eaten. Thus, the microhabitat and the body size of gammarids play dominant roles in prey selection by young red sea bream.     

A serine proteinase from the sarcoplasmic fraction of red sea bream Pagrus major is possibly derived from blood

Collagen degradation is known to be involved in the post mortem tenderization of fish muscle. A serine proteinase that is assumed to be related to collagen degradation after fish death was purified from the sarcoplasmic fraction of red sea bream Pagrus major by ammonium sulfate fractionation and column chromatography on Sephacryl S-300, Q Sepharose and Phenyl Sepharose CL-4B. The enzyme hydrolyzed gelatin and was obtained as a protein band of approximately 38 kDa upon sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions. The N-terminal amino acid sequence of the enzyme was determined for 32 residues. A protein that had the same N-terminal amino acid sequence as the enzyme for ten residues was purified from the serum of red sea bream and showed the same characteristics as the enzyme. Therefore, it is suggested that the serine proteinase migrates from the blood to muscle and degrades muscle proteins after the death of the fish.     

Genetic diversity of red sea bream Pagrus major in western Japan in relation to stock enhancement

SUMMARY: Stock enhancement is used in Japan as a tool to help the replenishment of wild populations of red sea bream Pagrus major . In this study, we analyzed the genetic diversity and composition of wild red sea bream at seven locations around Shikoku Island, South-west Japan, using three microsatellite loci. This analysis was done to test the hypothesis that: (i) red sea bream comprises a single Mendelian population along Japan; and (ii) stock enhancement programs around Shikoku Island are causing genetic differentiation among wild stocks. The results indicated that some locations from the Shikoku area were not significantly different from the rest of Japan, supporting the hypothesis of a single Mendelian population. Significant departures from Hardy–Weinberg equilibrium and significant pairwise F_ST among locations indicated genetic instability within this region. We suggest that the stock enhancement programs made in the region are the possible cause of this genetic instability. A management scheme for the hatcheries involved in the stock enhancement of red sea bream is presented.     

日本鹿儿岛湾真鲷的资源评估和增殖策略

通过世代分析对1990年至2002年鹿儿岛湾真鲷（Pagrus major）自然种群和放流种群的种群大小进行了评估,评估模型考虑了渔业资源管理和增殖放流措施。结果表明放流种群的规模有所减少,而自然种群的规模维持不变。真鲷自然种群的捕获量日趋减少,而放流种群的捕获量已超过50吨。研究结果表明增殖700000—800000尾真鲷种苗与其50吨的捕捞量相协调。在各种捕获量和放流量情况下,采用种群动力学模型预测了2017年真鲷的捕获量,其结果表明提高放流真鲷的数量能增加其捕获量。     

Purification and characterization of phospholipase A2 from the pyloric caeca of red sea bream, Pagrus major

A phospholipase A₂ was purified 55,000-fold in a yield of 10% from the lipid-free extract of powder of the pyloric caeca of red sea bream to near homogeneity by sequential column chromatography on S-sepharose fast flow, butyl-cellulofine, Asahipak ES-502C cation-exchange HPLC, TSK gel G3000SW gel-filtration HPLC, and Asahipak ODP-50 reversed-phase HPLC. The final preparation showed a single band with the apparent molecular mass of 14 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, and an estimated specific activity was 717 µmol min^-1 mg^-1 protein. The purified enzyme had a pH optimum in the range of pH 8.0–9.0 and required the presence of both 8 mM of Ca²⁺ and from 2 to 10 mM of sodium deoxycholate for its maximal activity, using 2 mM of phosphatidylcholine as a substrate. The purified enzyme preferentially hydrolyzed the 2-acyl ester bonds of both phosphatidylglycerol and phosphatidylcholine in the presence of sodium deoxycholate, followed in order by phosphatidylethanolamine and phosphatidyl-serine. In contrast to porcine pancreatic PLA₂, pyloric caeca PLA₂ hydrolyzed mixed-micellar phosphatidylcholine substrate effectively, regardless of the kinds of bile salts used. These results indicate that Ca²⁺-dependent low molecular mass PLA₂, so called secretory PLA₂, occurs in the pyloric caeca of red sea beam.     

Hypoxic conditions induce centrum defects in red sea bream Pagrus major (Temminck and Schlegel)

A previous study elucidated that an extreme hypoxia during somitogenesis induced the most frequent skeletal malformation centrum defects in red sea bream (RSB), Pagrus major. In this study, details of the hypoxic conditions to induce them in RSB, dissolved oxygen (DO) concentration and exposure time to hypoxia, were investigated. Fertilized eggs were exposed to seawater of six DO concentrations (0%, 10%, 25%, 50%, 75% and 100% of saturation) for seven different periods (5, 10, 30, 60, 120, 240 and 360 min) during somitogenesis. Somitic disturbances in newly hatched larvae were induced by exposure to 0% and 10% DO concentration for 10 and 120 min and longer respectively. Rearing eggs exposed to hypoxic condition of 10% DO for 240 min for 40 days post‐hatch showed that the location and the frequency of somitic disturbances in larvae and centrum defects in juveniles were significantly correlated (P<0.01). Dissolved oxygen concentration of the interstitial water in the egg high density layer formed at the water surface in a stationary state abruptly decreased to 3.7% within 7 min. Centrum defect induction by exposure of eggs to extreme low DO concentrations for a short period, which is the probable situation in the practical juvenile production, suggests that careful maintenance of DO concentration is important in the incubating water of fertilized eggs during egg sorting and transportation, where eggs are made into a pile and undergo hypoxia, for the prevention of centrum defects.     

Purification and characterization of phospholipase A2 isoforms from the hepatopancreas of red sea bream, Pagrus major1

Two phospholipase A₂ (PLA₂) isoforms, tentatively denoted as DE-1 and DE-2 PLA₂s, were purified from the hepatopancreas of red sea bream (Pagrus major) to near homogeneity by sequential column chromatography on S-Sepharose fast flow, DEAE-Sepharose fast flow and butyl-Cellulofine, and by ion-exchange, gel-filtration and reversed-phase HPLC. The purified DE-1 and DE-2 PLA₂s both showed a single band with the apparent molecular mass of approx. 13.5 kDa by SDS-polyacrylamide gel electrophoresis, and were found to be both related to group I PLA₂ based on the N-terminal amino acid sequences. DE-1 PLA₂ had a pH optimum in the alkaline region at around pH 10 and required approximately 10 mM of Ca²⁺ and 4-10 mM of sodium deoxycholate for its maximal activity, using 2 mM of phosphatidylcholine and phosphatidylethanolamine as substrates. DE-2 PLA₂ also had a pH optimum in the alkaline region at around pH 8-9 and required >10 mM of Ca²⁺ and approximately 6 mM of sodium deoxycholate for its maximum activity with 2 mM of phosphatidylcholine as a substrate; its enzymatic activity towards phosphatidylethanolamine was greatly inhibited by the addition of sodium deoxycholate. The results demonstrate that red sea bream hepatopancreas contains two enzymatically distinct group I PLA₂ isoforms.     

Oxygen deficiency during somitogenesis causes centrum defects in red sea bream, Pagrus major (Temminck et Schlegel)

Vertebral deformities in red sea bream, Pagrus major, remain serious obstacles to the improvement of seedling quality for its aquaculture. However, the causalities of the deformities remain unclear and prevention methods have not yet been established. In this paper, oxygen deficiency during somitogenesis was demonstrated to cause centrum defects (formerly called fused vertebrae in many cases), which are the major vertebral deformity in cultured red sea bream. An induction experiment of centrum defects was conducted by placing fertilized red sea bream eggs under low dissolved oxygen conditions (10.3–16.6%). The low oxygen treatment was carried out for five different developmental stages of embryo: two‐cell stage to blastula stage; gastrula stage; three to 10 somites stage; 11–17 somites stage and 18–24 somites stage. Oxygen deficiency during somitogenesis induced a high incidence of centrum defects. In contrast, it hardly induced centrum defects during the other stages. The dissolved oxygen concentration in the rearing water should be carefully regulated for fertilized eggs, especially during somitogenesis to reduce the incidence of vertebral deformities in the red sea bream.     

Morphological aspects of feeding and improvement in feeding ability in the early larval stages of red sea bream Pagrus major

The present study examined the appearance, ossification and growth of the bones that form the oral cavity in early larval stages of laboratory reared red sea bream ( Pagrus major ) for 380 h after hatching. The fundamental elements of the oral cavity appeared 11 h after initial mouth opening (HAMO). Development in the red sea bream, based on the osteological development of the feeding apparatus, was divided into three phases following the first feeding (24 HAMO; mean total body length 3.3 mm). The first phase was the early sucking phase (24 to 80–100 HAMO; approximately 3.9 mm), during which the head and bones increased in size. The intensified sucking phase (to 200–220 HAMO; approximately 4.9 mm) was defined by the appearance of new structural elements and a continued enlargement of the head and bones. Finally, during the transition phase (beyond 300 HAMO; approximately 5.6 mm), larvae used grasping as well as sucking to feed, new elements appeared, ossification began, size increased and teeth were acquired. As the larvae advanced through these three phases, the ability to feed by sucking was enhanced by the appearance and growth of new bones. The developmental phases appear to be linked to the transition from endogenous to exogenous nutrition resources under laboratory rearing conditions and to diversification in the size and components of wild food organisms.     

Studies on epizootic iridovirus infection among red sea bream,Pagrus major (Temminck & Schlegel), cultured in Taiwan

Since 1993, an epizootic viral disease has occurred in net-cage cultured red sea bream, Pagrus major (Temminck & Schlegel), in Peng-hu Island located on the south-western coast of Taiwan. The diseased fish exhibited abnormal swimming and were lethargic, but few visible external signs were observed. The cumulative mortality because of the disease sometimes reached 50-90% over 2 months. Histopathogical studies of the affected fish showed enlarged basophilic cells in the gill, kidney, heart, liver and spleen. These necrotic cells were Feulgen-positive and stained blue using Giemsa. Transmission electron microscopy revealed icosahedral virions in the cytoplasm of the necrotic cells. The viral particles consisted of a central nucleocapsid (75-80 nm) and envelope, and were 120-150 nm in diameter. These results suggest that the virus belongs to the Iridoviridae. Using polymerase chain reaction (PCR), approximately 570 bp fragments were produced from the viral DNA using as a template 1-F and 1-R primers derived from red seabream iridovirus (RSIV) from red sea bream in Japan. Similar results were also obtained using nested-PCR with different primer sets (1-F, 2-R and 2-F, 1-R). Although the size and some features of epizootics of this virus differed from RSIV in Japan, it shows close genetic affinities with the latter and it is suggested that RSIV has been introduced to Taiwan.