Inhibitory effect of 2,4-dibromophenol and 2,4,6-tribromophenol on larval survival and metamorphosis of the sea urchin <Emphasis Type="Italic">Strongylocentrotus nudus</Emphasis>

ABSTRACT:   As a possible factor leading to the low recruitment level of sea urchins in kelp forests, the inhibitory effect of 2,4-dibromophenol (DBP) and 2,4,6-tribromophenol (TBP) released from the large perennial brown algae Ecklonia kurome and Eisenia bicyclis on survival and metamorphosis of eight-armed larvae of the sea urchin Strongylocentrotus nudus was examined. The percentage of larvae that underwent metamorphosis in filtered sea water after 1 h exposure to one-half dilution of saturated dibromomethane solution (∼60 ppm) as a chemical inducer reached approximately 100% after 1 h, while that in filtered sea water containing 1 ppm TBP was reduced to 73%. This was further reduced to less than 40% in the presence of 10 and 20 ppm TBP after 2 h. In filtered sea water containing 1 and 10 ppm DBP, the proportion of metamorphosed larvae was reduced markedly to 43 and 5% after 2 h, respectively. All larvae exposed to 50 ppm TBP and to 20 and 50 ppm DBP died after 1 h. These findings suggest that DBP is more toxic than TBP for sea urchin larvae, strongly inhibiting their metamorphosis.     

Effect of starvation on biochemical composition and gametogenesis in the Pacific oyster <Emphasis Type="Italic">Crassostrea gigas</Emphasis>

The effects of starvation on biochemical composition and gametogenesis were investigated in the Pacific oyster Crassostrea gigas. Histological analysis, combined with oocyte examination and measurements of protein, glycogen and lipid levels and RNA/DNA ratio from gonad, adductor muscle and mantle tissue of each sex were performed. In the starved groups, C. gigas showed gonad development, but the progress was delayed during the experiment. Glycogen was the first substrate used by C. gigas for dealing with lack of food. While glycogen was rapidly consumed, protein and lipid contents decreased gradually. A decrease in the RNA/DNA ratio in the starved groups in all the body components was found during starvation, illustrating that RNA/DNA ratio was a valid indicator of nutritional condition in C. gigas. A significant increase in water and ash contents and a corresponding decrease in condition index were observed in the starved groups, showing that the water and ash content and condition index were related to the usage of glycogen, lipid and protein reserves in body composition. During starvation, energy reserves were mobilized for survival and gonad development, but spawning was arrested. The information obtained in this study is useful for broodstock management in the Pacific oyster industry.     

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.     

Universal PCR primers for ribosomal protein gene introns of fish

Human ribosomal protein (RP) gene sequences with respect to intron/exon structures and corresponding cDNA or genomic data of fish species were obtained from the GenBank database. Based on conserved exon sequences, 128 primer pairs for 41 genes were designed for exon-primed intron-crossing (EPIC) polymerase chain reaction (PCR). In reference to the draft genome sequences of the Pacific bluefin tuna (Thunnus orientalis), 12 primer pairs expected to amplify introns of the bluefin tuna with lengths of 500–1000 bp were selected and applied to six distantly related fish species belonging to the Orders Clupeiformes, Tetraodontiformes, Pleuronectiformes, Perciformes, Scorpaeniformes, and Anguilliformes. PCR amplification was observed for at least four species in each primer pair, and all fragments were larger than those expected for intronless amplification. Single fragment amplification was observed for at least seven primer pairs per species. Fragment sizes of the bluefin tuna for nine primer pairs corresponded to those expected from the genomic data. Thus, our primer pairs are potentially applicable to a wide variety of fish species and serve as an initial step for isolating single-copy nuclear DNA sequences.     

Replacement of fish oil with soybean oil in diets for juvenile Chinese sucker (<Emphasis Type="Italic">Myxocyprinus asiaticus</Emphasis>): effects on liver lipid peroxidation and biochemical composition

This study was designed to evaluate the effect of the replacement of fish oil (FO) by soybean oil (SO) on growth performance, liver lipid peroxidation, and biochemical composition in juvenile Chinese sucker, Myxocyprinus asiaticus. Fish (13.7 ± 0.2 g) in triplicate were fed five experimental diets in which 0% (FO as control), 40% (SO40), 60% (SO60), 80% (SO40), and 100% (SO100) FO were replaced by SO. The body weight gain of fish fed SO40, SO60, or SO80 diet was similar to FO group, but diets that have 100% soybean oil as dietary lipid significantly reduced fish growth (P < 0.05). Although the level of SO resulted in increasing crude lipid content of the liver, the level of SO did not significantly alter the hepatosomatic index (HSI). Indicators of peroxidation, such as vitamin E (V_E) and thiobarbituric acid-reactive substance (TBARS) contents, were changed as increasing dietary SO. It was shown that the inclusion of SO in the diets increased V_E concentrations, but reduced TBARS in the liver and total cholesterol (T-CHO) in the plasma. Linoleic acid (LA) and linolenic acid (LNA) significantly increased in fish liver fed diets that contained SO, but eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and the ratio n-3/n-6 were significantly reduced by the inclusion of dietary SO (P < 0.05). Our results indicated that the inclusion of SO increased the hepatic V_E content and reduced lipid peroxidation in fish. However, diet containing 100% SO as dietary lipid could reduce growth performance. Thus, we recommended that 40–80% SO can be used as dietary lipid to replace FO for juvenile Chinese sucker.     

Identification of oyster-derived hypotensive peptide acting as angiotensin-I-converting enzyme inhibitor

Angiotensin-I-converting enzyme (ACE) plays a crucial role in the crisis of hypertension. Some peptides that originate from protease hydrolysates are known to suppress ACE activity in vitro and in vivo. Here, we investigated whether trypsin hydrolysate of oyster Crassostrea gigas showed hypotensive activity and ACE inhibition. The hydrolysate significantly suppressed systolic blood pressure and ACE activity in spontaneously hypertensive rats following a one-shot oral administration and a long-term feeding experiment lasting 9 weeks. Each hydrolysate from oyster tissue showed ACE inhibitory activity, indicating the hypotensive effect was due to synergism. One potent ACE inhibitory peptide, Asp-Leu-Thr-Asp-Tyr, was identified from the hydrolysate of the striate muscle, and the peptide exhibited hypotensive activity in vivo. Protease digestion analysis suggested that Asp-Tyr could be the real effector of this penta-peptide in vivo.     

Androgen-induced pseudo-hermaphroditic phenotypes in female <Emphasis Type="Italic">Brevimyrus niger</Emphasis> Günther 1866 (Teleostei,Mormyridae)

This paper explores the plasticity of sexually dimorphic characters in subadult female Brevimyrus niger, an African weakly electric mormyrid species. Thirty-five fish were exposed in a staggered fashion (five fish a week) to aromatizable 17α-methyltestosterone over a period of 7 weeks; 18 fish served as untreated controls. 17α-MT induced precocious vitellogenesis that mirrored the natural maturational process during seasonal ovarian recrudescence. At the same time, 17α-MT exposure resulted in complete masculinization of the females’ anal fin support structure normally observed during rainy season in adult males. We discuss possible hormonal mechanisms acting along the brain-pituitary-gonad axis that would explain the occurrence of precocious vitellogenesis and the male-typical transformation of the female’s anal fin ray bases. Our findings are relevant to commercial aquaculture as the use of 17α-MT in fish hatcheries can pose serious environmental issues.     

Growth comparison of Asian Nile and red tilapia strains in controlled and uncontrolled farm conditions

Growth of several genetically improved Nile tilapia (GIFT or Genetically Improved Farmed Tilapia, FaST or Freshwater Aquaculture Center Selected Tilapia, SEAFDEC-selected) and domesticated red tilapia (BFS or Binangonan Freshwater Station, NIFI-red or National Inland Fisheries Institute red, HL or Hacienda Luisita) stocks were compared in controlled (tank) and uncontrolled farm conditions (lake-based cages) with unselected NIFI or Chitralada Nile tilapia as control. Specific growth rate differed significantly (P = 0.009) in tank-reared Nile tilapia stocks where GIFT grew best at 1.358%/day followed by FaST (1.307%/day), control stock NIFI (1.257%/day) and SEAFDEC-selected (1.202%/day). Genetic effect explained 84.4% of the variance in growth of Nile tilapia in tanks. Although Nile tilapia growth in cages followed the same trend where GIFT grew best at 1.570%/day, no significant stock differences (P = 0.479) were noted. Meanwhile, red tilapia reared in either tanks or cages showed no significant stock differences in terms of growth. However, survival of the red tilapia stocks in cages differed significantly with HL having the highest percentage survival at 93.3%. The different growth responses of the Nile tilapia stocks especially under controlled (tank) farm conditions were largely due to genetic factors (stock differences).Under uncontrolled farm conditions, environmental factors were generally observed to have also affected the survival and to some extent, the growth of Asian Nile and red tilapia stocks.     

Effect of dietary <Emphasis Type="SmallCaps">l</Emphasis>-tryptophan on cannibalism,survival and growth in pikeperch <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.) post-larvae

The effect of supplemented commercial diets with crystalline l-tryptophan (TRP—5, 10 and 20 g TRP kg^?1) on cannibalism, survival and growth parameters of pikeperch post-larvae (Sander lucioperca) was evaluated. Fifteen-day-old pikeperch larvae (mean weight—6.8 mg) were reared during the next 28 days (20.5 °C, 16L:8D) in glass aquaria in a recirculating aquaculture system. The enzyme-linked immunosorbent assay showed that TRP-supplemented diets were effective in increasing the levels of serotonin (5-HT) in the body tissue of pikeperch. TRP supplementation resulted in a slight decrease in both types of cannibalism, although the reduction in cannibalism impact did not amount to more than a few percent. TRP treatment had no significant influence on the final survival of pikeperch post-larvae (ranged from 20.1 ± 12.4 to 29.0 ± 12.9 %). However, contrary to the earlier studies conducted on other fish species, no significant difference in the growth rates and feeding behavior of pikeperch between TRP-fed and control group were found. The final body weight and growth rate ranged from 0.211 ± 0.014 to 0.243 ± 0.016 and from 12.19 ± 0.38 to 12.76 ± 0.35 % day^?1, respectively. To our knowledge, this is the first study reporting the effects of TRP supplementation on the cannibalism–survival–growth relations in fish in the post-larval stage.     

Low water exchange Gracilariopsis bailiniae Zhang & B.M. Xia culture in intensive milkfish culture effluents: effects of seaweed density on seaweed production and effluent treatment

This study tested the feasibility of a low-cost seaweed biofiltration system for pond-based aquaculture through an indoor-integrated fish-seaweed culture experiment using weekly nutrient supply regime and different seaweed stocking densities. The culture experiment was conducted in glass aquaria that were stocked with Gracilariopsis bailiniae at 3 densities (low = 0.5 kg m^?2, middle = 2 kg m^?2 and high = 3.5 kg m^?2) and provided either with effluents from intensive milkfish (Chanos chanos) culture or with effluent-free seawater (control) as nutrient source. Stocking density was used as a factor in optimizing nutrient availability for growth and nutrient removal under such low water exchange conditions. Our results showed that G. bailiniae cultivated in milkfish effluents had higher growth, biomass and nitrogen yields than those cultivated in effluent-free seawater. Among the different stocking densities tested, highest growth rate (1.03 % day^?1) was obtained in the middle density. Increasing biomass and nitrogen yields were also obtained at this density until the end of the culture period. Poorer growth rates at low and high stocking densities were attributed to light limitation from phytoplankton and self-shading, respectively. Due to seaweed treatment, average outflow concentration of NH₄ ⁺ was reduced from half of its pretreated level. This study showed that a weekly effluent supply at 2 kg m^?2 seaweed stocking density can sustainably support the growth of G. bailiniae as long as the dissolved nutrients are present at high levels.