Morphological studies of peripheral blood cells of the Chinese sturgeon, <Emphasis Type="Italic">Acipenser sinensis</Emphasis>

The peripheral blood cells of one-year-old Chinese sturgeon (Acipenser sinensis) have been studied by light microscopy and transmission electron microscopy. The erythrocyte count was 84.86 × 10⁴ cell mm⁻³ in the peripheral blood of the fish and that of leukocytes was 2.24 × 10⁴ cell mm⁻³. The erythrocytes and four main types of leucocyte—thrombocytes, lymphocytes, granulocytes (including neutrophils and eosinophils), and monocytes, were identified in the peripheral blood. In addition to normal erythrocytes, reticulocytes and division of erythrocytes were observed. Thrombocytes were the most numerous among the leukocytes, and the number of neutrophils with lobated nuclei was larger than for other fish. The structures of the erythrocytes, lymphocytes, monocytes, granulocytes, and thrombocytes of the fish were studied. The erythrocytes were almost completely devoid of organelles, except for some mitochondria and granules. A large number of vacuoles and a few organelles were observed in cytoplasm of the monocytes. There were many microvilli on the membrane and pseudopodia-like cytoplasm bulge in the lymphocytes. The neutrophils were round or oval in shape with bilobed, trilobed, or multilobed nuclei whereas the eosinophils had big special granules, dark stained. There were many vesicles in some thrombocytes, which were related to its phagocytosis; some thrombocytes had almost no cytoplasm or organelles.     

Effects of mangrove deforestation on fish assemblage at Pak Phanang Bay,southern Thailand

Daytime sampling using a seine net was conducted at Pak Phanang Bay (Nakhon Si Thammarat Province, Thailand) in February and July 2006, to determine differences in fish assemblage structures between a mangrove site and an adjacent site completely cleared of mangroves. The overall numbers of fish species and individuals were significantly higher at the mangrove site than the cleared site in both months. Although benthic crustacean feeders showed more species and individual numbers at the mangrove site in both months, the opposite was found for zooplankton feeders. A cluster analysis, based on the abundance of each species, demonstrated that the fish assemblage structures were distinctly different between the two sites. In addition, significant differences in length frequency distributions for each of the four most abundant species were found between the sites in February and/or July. Small individuals of Scatophagus argus, Ambassis nalua, and Tetraodon nigroviridis were more common at the mangrove site, and of Chelon subviridis at the cleared site. These results suggest that mangrove deforestation exerts marked effects on fish assemblages.     

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.     

Relationship between soak time and number of enmeshed animals in experimentally lost gill nets

In order to determine the effects of ghost fishing by lost gill nets, the relationship was examined between soak time and number of enmeshed animals in experimentally lost gill nets by using diving observations. Two experimental gill nets were set at 13 m depth in Tateyama Bay, Chiba Prefecture, Japan for approximately 200 days. One gill net was deployed in a small trough surrounded by artificial reefs, and the other was deployed on an adjacent open sandy bed. Twelve species of crustaceans, six species of gastropods, and five species of bony fish were enmeshed in the experimental gill nets. The number of enmeshed animals in the artificial reef gill net was substantially larger than that in the sandy bed gill net. The number of enmeshed animals in the experimental gill nets increased rapidly within one month after deployment, and then declined gradually showing fluctuations caused by the decrease in newly enmeshed animals, and the drop off from gill nets caused by the decomposition of dead animals. The decrease in the number of enmeshed animals was expressed by logarithmic equations, and based on these equations, the duration of capture function for the lost gill nets was calculated to be 284–561 days in the artificial reef gill net and 200 days in the sandy bed gill net. The duration of capture function for the lost gill nets for non-commercial by-catch species such as small crustaceans and gastropods was longer than for commercial species such as Japanese spiny lobster and bony fish.     

Determination of the quality parameters of pike perch <Emphasis Type="Italic">Sander lucioperca</Emphasis> caught by gillnet,longline and harpoon in Turkey

ABSTRACT:   The effects of the different catching methods (gillnet, longline, harpoon) on sensory, chemical (pH, total volatile base nitrogen, K -value) and microbiological (total viable count [TVC]) changes in pike perch Sander lucioperca stored in ice were investigated. The same soaking time was used for both gillnet and longline fishing. The catching method had considerable influence on the freshness quality of pike perch. The acceptable shelf life was 15 days for pike perch caught by gillnet, and 22 days for longline and harpoon. The initial concentrations of inosine monophosphate (2.4 μmol/g) in pike perch caught by gillnet were significantly lower ( P  < 0.05) than longline (4.1 μmol/g), and especially by harpoon (16.7 μmol/g). However, the initial K -values for fish caught by harpoon were significantly ( P  < 0.05) lower (24.36%) than fish caught by longline and gillnet (57.69%, 64.41%, respectively). The average K , Ki, G and H -values at rejection day in terms of sensory assessment were approximately 90, 98, 156 and 40%, respectively, for all catching methods during ice storage. However, TVC reached 7.0 log cfu/g after approximately 11 days of storage for fish caught by gillnet, 19 days for fish caught by longline and 8 days for fish caught by harpoon. The result of this study suggests that the best catching method for preserving the freshness of pike perch is longline, based on the data obtained from the sensory and microbiological analysis.     

Carbon source and trophic position of pelagic fish in coastal waters of south-eastern Izu Peninsula,Japan, identified by stable isotope analysis

ABSTRACT:   It is important to clarify trophic dynamics in marine ecosystems for management of the fishing ground. Organic carbon sources and trophic position of pelagic fishes in the coastal waters of the south-eastern Izu Peninsula, Japan, were examined on the basis of carbon and nitrogen stable isotope distributions. The δ¹³C of the fishes was mostly distributed from −19 to −16‰ for nektonic fishes (13 species of adults and immatures) and planktonic fishes (10 species of larvae and juveniles), close to the δ¹³C values of particulate organic matter and planktonic decapods. These δ¹³C signatures for the inhabitants of the water column were in contrast with the high δ¹³C values (mainly −16 to −13‰) for demersal fishes of Scorpaeniformes and benthic polychaetes collected in the surf zone. These results indicate that nektonic and planktonic fishes depend on phytoplankton for carbon supply. The δ¹⁵N signatures suggest that the trophic position ranged 3.1–4.5 for the nektonic fishes and 2.9–3.7 for the planktonic fishes, premised on trophic level 3 for larval Japanese anchovy Engraulis japonicus . Thus, planktivorous fishes should be mainly assigned to trophic levels 3 and 4 in this area.     

Post-release movement and diel activity patterns of hatchery-reared and wild black-spot tuskfish <Emphasis Type="Italic">Choerodon schoenleinii</Emphasis> determined by ultrasonic telemetry

ABSTRACT:   Post-release movement and diel activity patterns of hatchery-reared and wild black-spot tuskfish were examined using ultrasonic telemetry. Five hatchery-reared and four wild fish were released in the sandy bottom of Urasoko Bay, Ishigaki Island, Okinawa, Japan, and monitored using automated monitoring receivers from November 2005 to February 2006. Both hatchery-reared and wild fish tended to stay near the release site for over two weeks, before leaving the release site. Both hatchery-reared and wild tuskfish showed diurnal rhythm intermittently; signals were recorded more frequently in the daytime and less frequently in the nighttime, suggesting that the fish of both origins were active during the day and inactive during the night. These findings indicate that the one-year-old hatchery-reared tuskfish have some consistent behavioral characteristics with those of the wild.     

Substitute and complement relations among various fish species in the Japanese market: implications for fishery resource management

A demand system analysis was conducted to examine the substitute relationships between tuna and skipjack tuna in the Japanese market. Data from the Annual Report on Family Income and Expenditure Survey from 1965 to 2006 were used for the analysis using the almost ideal demand system (AIDS). Results suggest that skipjack tuna can be a strong substitute for tuna, while other fish groups are not a clear substitute. Our analysis of substitute relationships among fish species in a market indicates that this is a factor that should be considered for better fisheries resource management. For instance, even under a situation where one fish species is underexploited, proper attention to its fishery management is necessary if the fish is a strong substitute for another popular fish species in the market.     

Physiological response,blood chemistry profile and mucus secretion of red sea bream (<Emphasis Type="Italic">Pagrus major</Emphasis>) fed diets supplemented with <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> under low salinity stress

Environmental stressors caused by inadequate aquaculture management strategies suppress the immune response of fish and make them more susceptible to diseases. Therefore, efforts have been made to relieve stress in fish by using various functional feed additives in the diet, including probiotics. The present work evaluates the effects of Lactobacillus rhamnosus (LR) on physiological stress response, blood chemistry and mucus secretion of red sea bream (Pagrus major) under low salinity stress. Fish were fed four diets supplemented with LR at [0 (LR0), 1 × 10² (LR1), 1 × 10⁴ (LR2) and 1 × 10⁶ (LR3) cells g^?1] for 56 days. Before stress, blood cortisol, urea nitrogen (BUN) and total bilirubin (T-BIL) showed no significant difference (P > 0.05), whereas plasma glucose and triglyceride (TG) of fish-fed LR2 and LR3 diets were significantly lower (P < 0.05) than those of the other groups. Plasma total cholesterol (T-CHO) of fish-fed LR3 diet was significantly (P < 0.05) lower than that of the other groups. Furthermore, total plasma protein, mucus myeloperoxidase activity and the amount of mucus secretion were significantly enhanced in LR-supplemented groups when compared with the control group (P < 0.05). After the application of the low salinity stress test, plasma cortisol, glucose, T-CHO and TG contents in all groups showed an increased trend significantly (P < 0.01) compared to the fish before the stress challenge. However, plasma total protein and the amount of secreted mucus showed a decreased trend in all groups. On the other hand, BUN, T-BIL and mucus myeloperoxidase activity showed no significant difference after exposure to the low salinity stress (P > 0.05). In addition, the fish that received LR-supplemented diets showed significantly higher tolerance against low salinity stress than the fish-fed LR-free diet (P < 0.05). The physiological status and the detected immune responses, including total plasma protein and mucus myeloperoxidase activity in red sea bream, will provide a more comprehensive outlook of the effects of probiotics to relieve stress in fish.