Transfer of PCDDs and PCDFs into the edible parts of farmed rainbow trout, Oncorhynchus mykiss (Walbaum), via feed

This study was carried out to quantify the transfer of polychlorinated dibenzo‐p‐dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from commercial fish feed into the edible part of rainbow trout (Oncorhynchus mykiss, Walbaum) under normal rearing conditions. Trout were fed with high‐energy feed for salmon (fat content 26–30%) over a period of 19 months. The average weight of the fish increased from 10 g to more than 2092 g, reaching a size of up to 51‐cm length (Tl). Considerable amounts of PCDDs and PCDFs were transferred from the fish feed into the tissue of the trout. Dioxin concentrations increased during the time of feeding from 0.054 up to 0.914 ng WHO‐PCDD/F‐TEQs kg^?1 wet weight and from 4.991 to 15.815 ng WHO‐PCDD/F‐TEQs kg^?1 fat. A correlation was found between the dioxin concentration of the feed and the resulting concentration in the fat of the muscle tissue. The data allow the establishment of transfer rates from a high‐energy diet to farmed rainbow trout.     

Australia‘s Lake Eacham rainbow fish: lessons and outlook

Recent DNA comparisons confirm that the endangeredLake Eacham rainbow fish (Melanotaenia eachamensis Allen andCross, 1982) is a separate species, distinct from othermelanotaeniids in the area. Although the large populationformerly in Lake Eacham has not been re-established, other smallnatural populations of M. eachamensis have been identified fromLake Euramoo and Dirran Creek.Commencing with 23 captive individuals (3 14 6 I), representing three original stocks, Project Eachamensis (initiated by the Australia New Guinea Fishes Association in July 1987) has stimulated and actively encouraged the establishment of new captive populations. Approximately 15 captive breeding populations are now reported in eastern Australia -- numbers of individuals are estimated to exceed 1000; additional Bowman and Tappin populations are being maintained in North America and Europe.A recent review of this conservation programme (involving individual aquarists, hobbyist organizations and scientists as well as the aquarium industry and government) has now recommended: an alteration to the conservati on status category from endangered to vulnerable; maintenance of existing captive populations; formulation of a comprehensive recovery plan with the long-term objective of re-establishing and increasing natural populations; and encouraging public education on the risks of translocation.     

Effects of the protein/carbohydrate ratio of extruded diets on protein synthesis, protein growth and body composition in juvenile brown trout (Salmo trutta)

High levels of protein in fish feeds result in higher costs and nitrogen waste. Therefore, studies focused on protein substitution by alternative energy sources are necessary. Here we examine whether the protein:carbohydrate ratio in extruded diets affects protein-turnover parameters and the main tissue components in brown trout. Juvenile fish were adapted to two extruded diets: one higher in protein and lower in carbohydrate, C: 45/28 and the other higher in carbohydrate and lower in protein, HC: 37/40. Gross energy was 19 MJ kg⁻¹ DM in both diets. Protein and lipid digestibility were high and similar in both groups (≈90%), whereas total and carbohydrate digestibility and digestible energy were lower in the HC-fed group than in the C-fed group. Consequently, when fish were adapted to the diets, plasma levels of glucose and insulin differed between diets. HC-group presented higher plasma glucose levels and lower plasma insulin levels than C-group. Protein synthesis rates in white muscle, liver and whole body did not differ significantly between diets. In contrast, protein accretion rate of white muscle and whole body were significantly lower in the HC group, indicating an increase of protein degradation in these tissues and a decrease of synthesis retention efficiency. In spite of the daily protein intake of HC group was lower than C-group, the anabolic stimulation efficiency was increased by 34% in HC group. Protein and lipid contents in white muscle and liver were stable throughout the experiment. No hepatomegalia or increased fat deposition was observed in fish fed HC. Differences in specific growth rates (C: 0.88%; HC: 0.77%) were associated more with the lower protein consumption rate and the lower level of digestible energy in fish fed HC than with the higher dietary carbohydrate content of the diet.     

Effects of changes in plasma pH,CO2 and ammonia on ventilation in trout

We investigated ventillatory responses to a plasma alkaloids and hypocapnia,a nd the basis for the ventilatory response to sodium bicarbonate (NaHCO₃) infusion in rainbow trout. Plasma alkalosis and hypocapnia created by infusion of sodium hydroxide (NaOH) did not cause hypoventilation, whereas infusion of hydrochloric acid (HCl) caused vigorous hyperventilation, associated with an acidosis, a reduction in blood O₂ content (Ca_{O 2}) and a release of circulating catecholamines. Infusion of NaHCO₃ stimulated ventilation and caused an increase in plasma pH, total carbon dioxide content (Ca_{CO 2}) and catecholamine levels, and a reduction in oxygen tension (Pa_{O 2}). Infusion of ammonium bicarbonate (NH ₄HCO₃) caused hyperventilation and was associated with an increase in Ca_{CO 2} and plasma total ammonia (C_amm) and ammonia gas (NH₃) concentration. Infusion of sodium chloride (NaClI) and Cortland's saline had no effect on ventilation. The results indicate that trout do not exhibit the ventilatory sensitivity to pH seen in terrestrial vertebrates. Ventilatory responses to NaHCO₃ appear to have been a result of reductions in Pa_{O 2}, a release of catecholamines and an increase in Ca_{CO 2} whereas responses to NH₄HCO₃ appear to have been a result of increases in Ca_{CO 2} and C_amm.     

The nature of hematological response in fish

Hematological status was examined in rainbow trout,Oncorhynchus mykiss, held for 3–4 weeks under temperature, photoperiod and P_{O 2} conditions approximating those of their winter, spring and summer habitats. The most striking change observed was in red cell population composition. In winter fish mature cells were predominant; juvenile and developing erythrocytes characterized spring and summer animals. Hemoglobin, hematocrit and both mean erythrocytic volume and hemoglobin were modestly lower in spring and summer than in winter fish. Red cell numbers were not significantly affected. These observations suggest that avoidance of viscosity-based increases in circulatory work cost is more advantageous than elevation of blood O₂-carrying capacity. Although hemoglobin isomorph profiles were significantly altered, there is little evidence that such changes are of critical adaptive importance. Given presumed age-based reduction in gas transport effectiveness, the replacement of mature and senescent cells by more metabolically-competent juvenile cells appears to be the pivotal event in hematological response. Leucocyte counts were significantly elevated in spring and summer as compared to winter fish. Lymphocyte/heterophil ratios declined from 8.27 in winter fish to 3.13 in summer trout. Thrombocyte, monocyte, eosinophil and basophil abundances were little changed.     

Dietary microbial phytase supplementation and the utilization of phosphorus, trace minerals and protein by rainbow trout [Oncorhynchus mykiss (Walbaum)] fed soybean meal-based diets

Effects of thermal and enzymatic treatments of soybean meal on apparent absorption of total phosphorus, phytate phosphorus, nitrogen (protein), ash, calcium, magnesium, copper, iron, manganese, strontium and zinc were examined using rainbow trout, Oncorhynchus mykiss (Walbaum), as the test species. Absorption of the test nutrients was estimated using yttrium as an inert non-absorbable indicator. Thermal treatments (microwaving, dry roasting, steam heating, cooking) had no measurable effect on the apparent absorption of phosphorus and other minerals. Phytase supplementation increased the apparent absorption of phosphorus, nitrogen (protein), ash, calcium, magnesium, copper, iron, strontium and zinc in low-ash diets containing soybean meal, but had little effect in high-ash diets containing both soybean and fish meal. In low-ash diets, the apparent absorption of phosphorus increased in accord with the level of phytase added to the diet, from 27% (no phytase added) up to 90% (phytase added, 4000 units kg⁻¹ diet) or 93% (predigested with phytase, 200 units kg⁻¹ soybean meal). In high-ash diets, dietary acidification with citric acid decreased the effect of phytase, whereas in low-ash diets, acidification markedly increased the effect of the enzyme. Excretion of phosphorus in the faeces of fish fed a low-ash diet containing phytase-treated soybean meal was 0.32 g per kg diet consumed, a 95%−98% reduction compared with phosphorus excretion by fish consuming commercial trout feeds.     

Cortisol does not affect hepatic α- and β-adrenoceptor properties in rainbow trout (Oncorhynchus mykiss)

Distribution and function of hepatic - and -adrenoceptors were examined in rainbow trout (Oncorhynchus mykiss) injected with slow release hydrogenated coconut oil implants alone (sham) or containing cortisol. - and -Adrenoceptors were assayed on purified hepatic membranes 10–14 days post-implantation using ³H-prazosin () and ³H-CGP (). At 10–14 days, plasma cortisol values were significantly elevated to approximately 220 compared with 35.0 ng ml^-1 in cortisol implanted vs. sham trout. No significant differences were found between any of the experimental groups for either the affinity (K_d) or maximal number of binding sites (B_max) for either receptor type. Epinephrine significantly stimulated glucose release from hepatocytes isolated from sham injected trout, but not from cortisol-treated fish. Epinephrine-induced glucose release was blocked by both - and -antagonists. These studies do not support the hypothesis that rainbow trout exposed to chronic cortisol alter properties of hepatic adrenoceptors.     

我国养鳟面临的问题及其对策探讨

本文总结我国虹鳟引进至今在消化吸收及国产化方面所取得的进展及当前存在的主要问题.并提出今后我国养鳟业应以专业户为主,加强对现有鳟鱼场的管理,挖掘潜力,建立全国流通体系.南方养鳟可土池、水泥池并举以降低成本在技术管理上需予注意三个问题.