Development of an in vitro culture system for producing eel larvae from immature ovarian follicles in Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis>

To standardize conditions during the final maturation and ovulation of ovarian follicles from Japanese eel, we have developed a culture system for the production of fertilizable eggs from post-vitellogenic ovarian follicles in vitro. Post-vitellogenic ovarian follicles were incubated in culture medium supplemented with 17α,20β-dihydroxy-4-pregnen-3-one (DHP) with or without bovine serum albumin (BSA) to assess the effects of protein concentration. Eggs that ovulated during incubation were fertilized, and the remaining follicles were incubated in prostaglandin F_2α (PGF_2α) for a further 3 or 6 h before fertilization. Male eels were injected repeatedly with human chorionic gonadotropin. The quality of eggs obtained under the different culture conditions was evaluated after artificial fertilization in terms of hatching success. Hatching rates tended to decrease with increasing concentrations of BSA in the incubation medium in a dose-dependent manner. The addition of PGF_2α drastically increased the number of eggs that ovulated, but the rate of hatching was greatly decreased compared with eggs obtained earlier by DHP incubation alone. The larvae obtained from artificially fertilized eggs produced in vitro survived for 14 days without feeding. We conclude that in vitro culture systems thus have a great potential for the acquisition of good quality eggs under tightly controlled artificial conditions, culminating in the production of eel larvae.     

Effect of N-acetyl cysteine and glycine supplementation on growth performance,glutathione synthesis,and antioxidative ability of grass carp, <Emphasis Type="Italic">Ctenopharyngodon idella</Emphasis>

An 8-week feeding trial was conducted to evaluate the effect of N-acetyl cysteine (NAC) and glycine supplementation on growth performance, glutathione (GSH) synthesis, and antioxidative ability of grass carp, Ctenopharyngodon idella. Four practical diets were formulated: control, control + 0.2% NAC, control + 0.5% glycine, and control + 0.2% NAC + 0.5% glycine. Each diet was randomly assigned to quadruplicate groups of 30 fish (approximately 8.8 g). Weight gain and specific growth rate were significantly increased with the supplementation of NAC. Supplementation of NAC plus glycine significantly increased the feed efficiency. Glutathione peroxidase (GPx) and γ-glutamine cysteine synthase (γ-GCS) in plasma were significantly increased with the supplementation of NAC plus glycine. GSH in plasma increased and malondialdehyde (MDA) decreased in fish fed diets supplemented with NAC. Respiratory burst, superoxide dismutase (SOD), and catalase (CAT) activity were not affected by NAC or glycine. These results clearly indicated that NAC improved the growth performance and restored GSH of grass carp, supplemented NAC together with glycine enhanced GSH synthesis, and improved the antioxidative ability of grass carp.     

Comparison of early life history stages of the bay scallop, Argopecten irradians: Effects of microalgal diets on growth and biochemical composition

The culture of bay scallops, Argopecten irradians, is limited by a reliable and affordable supply of spat and the ability to ensure that animals attain market size within a single growing season. The main goals of our study were thus: (1) to develop growth-optimizing algal diets for implementation in hatcheries, and (2) to identify and compare bay scallop postlarval and juvenile dietary requirements, especially of lipids and fatty acids, which if met may enhance production. Nutritional needs of postlarval bay scallops (present study) are compared with those of sea scallops, Placopecten magellanicus, offered the same diets in a previous companion study. To this end, postlarval (initial shell height, SH = 240 μm) and juvenile (initial SH = 10 mm) bay scallops were offered 6–7 microalgal diet combinations at 20 °C, for 3 weeks. A similar growth ranking among diets was observed between the two developmental stages. A combination diet of Pavlova sp. (CCMP 459) and Chaetoceros muelleri was far superior to any other diet tested, yielding growth rates of 58 and 357 μm day^− 1 which were 65% and 25% higher than the next highest performing diet of Tetraselmis striata/C. muelleri in postlarvae and juveniles, respectively. The T. striata/C. muelleri diet, which is limited in the n-3 fatty acid docosahexaenoic acid (DHA), yielded very poor growth of sea scallop postlarvae in a prior study, indicating that bay scallops may have less stringent requirements for DHA than sea scallops. The Pav 459/C. muelleri diet, which also supported the highest growth of sea scallop postlarvae, is characterized by elevated levels of the n-6 fatty acids, arachidonic (AA) in C. muelleri and 4,7,10,13,16-docosapentaenoic (DPA) in Pav 459. The two diets deficient in AA and n-6 DPA, Pavlova lutheri/Thalassiosira weissflogii and P. lutheri/Fragilaria familica, yielded the lowest growth rates in both bay scallop postlarvae and juveniles. Tissue enrichment of these two fatty acids relative to the diet, as well as overall enrichment in ∑n-6 fatty acids was observed across developmental stages and dietary treatments. A similar pattern has previously been observed in sea scallop postlarvae, suggesting a dietary requirement for n-6 fatty acids in pectinids that has often been overlooked in the past.     

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.     

Capricious bioinvasions versus uncoordinated management strategies: how the most unlikely invaders can prosper under the current UK legislation framework

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The development of the Norwegian wrasse fishery and the use of wrasses as cleaner fish in the salmon aquaculture industry

Norway leads the world aquaculture production of Atlantic salmon Salmo salar and farmed Norwegian Atlantic salmon is currently consumed around the globe. However, sea lice infestation is a major problem faced by the salmon aquaculture industry in Norway and elsewhere. The use of wild-caught cleaner fish, mainly wrasses, has been recommended over the other available methods as the most economical and environmentally friendly option to control sea lice infestation in salmon farming. Here, we review the development of the Norwegian wrasse fishery and the use of wrasses as cleaner fish. In this document, we address the sea lice problem and introduce the main wrasse species employed as cleaner fish, document the cleaning behaviour of wrasses, present the development of a new wrasse fishery associated with the salmon aquaculture industry, and finally, we identify the main challenges associated with the intensive use of wild-caught cleaner wrasses and provide some insight for future directions of the wrasse fishery and further development of aquaculture techniques to supply salmon facilities with domesticated cleaner fish.     

Cannibalism among <Emphasis Type="Italic">Lithodes santolla</Emphasis> (Molina 1782) juveniles: effect of stocking density,stage and molt condition

Losses of king crabs (deaths) in massive rearing conditions are frequently attributed to cannibalism. As several factors could influence cannibalism intensity during culture, the aim of the present study was to determine the effect of molt condition, stage and density on cannibalism among Lithodes santolla juveniles. Comparisons between intermolt and molt conditions and between C1 and C2 stages during intermolt were performed at three densities (6, 12 and 18 individuals per flask; that is equivalent to 236, 472 and 708 individuals m^?2). After 16 days of juvenile coexistence, cannibalism (injured + dead) was higher during molting (33.9 ± 4.5 %) than intermolt (21.7 ± 3.9 %), even though only 36 % of crabs had molted. Although cannibalism was similar in C1 and C2 stages, the proportion of dead animals was higher by a factor of three in C1 stage, probably due to the fact that animals reach the first juvenile stage with low energetic reserves, after the lecithotrophic larval development. Density was the main factor influencing cannibalism in our experiments. Higher densities promoted higher deaths, while agonistic interactions evidenced by injured crabs remained constant. Walking appendages were lost more often than chelipeds during first agonistic encounters. We recommend the use of intermediate densities (450 crabs m^?2 at most), the early detection of exuviae and the sorting of crabs after molting, for L. santolla rearing.     

Effects of light intensity on molting,growth, precocity,digestive enzyme activity,and chemical composition of juvenile Chinese mitten crab <Emphasis Type="Italic">Eriocheir sinensis</Emphasis>

A 74-day growth trial was carried out to investigate the effects of light intensity on the juvenile Chinese mitten crab, Eriocheir sinensis, under semi-natural conditions. The experiment had three light intensity treatment groups, natural light (NL), middle light (ML), and low light (LL), as light intensity became weaker. The results indicated that light intensity had no significant effect on molting interval and molting frequency but did have a significant effect on the molting weight gain of the crab. Molting weight gain in group NL was significantly higher than that in group LL (P < 0.05). Specific growth rate in weight (SGRw) and in carapace width (SGRcw), weight gain, and final body weight were significantly affected by light intensity (P < 0.05). No significant difference was detected in survival between groups (P > 0.05). The precocious rate in groups NL, ML, and LL was 26.14, 15.48, and 17.14%, respectively. The precocious rate in group NL was significantly higher than that in groups ML and LL (P < 0.05). Chemical composition of the crab body was significantly affected by light intensity, but the activity of alkaline phosphatase, trypsin, and pancreatic lipase was not significantly affected by light intensity. The results indicated that the submitted light intensity was useful in reducing the precocious rate without affecting the normal growth of juvenile E. sinensis.     

Species identification method for <Emphasis Type="Italic">Scombrops boops</Emphasis> and <Emphasis Type="Italic">Scombrops gilberti</Emphasis> based on polymerase chain reaction-restriction fragment length polymorphism analysis of mitochondrial DNA

ABSTRACT:   Gnomefish Scombrops boops and Scombrops gilberti are commercially important fishes in Japan, but these species are often confused in the markets because of their morphological similarity. To identify these two species, we performed nucleotide sequencing and restriction fragment length polymorphism (RFLP) analysis on 16S ribosomal RNA (rRNA) gene and the control region in mitochondrial DNA. Five and 12 nucleotide substitutions were observed between species in the 777-bp 16S rRNA gene and 471-bp control region, respectively. Diagnostic restriction sites for discriminating between S. boops and S. gilberti were found in the 16S rRNA gene, but not in the control region. Polymerase chain reaction (PCR)–RFLP analysis using two enzymes, Eco NI and Mva I, clearly discriminated between S. boops and S. gilberti identified by meristic characters. The PCR–RFLP analysis identified most of the 168 Scombrops young caught in the coastal waters of the Izu and Miura peninsulas as S. boops , suggesting that S. gilberti juveniles are rare in this area.