The use of AquaMats® to enhance growth and improve fin condition among raceway cultured rainbow trout Oncorhynchus mykiss (Walbaum)

AquaMats® are a type of artificial seaweed designed to provide structure in ponds used for fish culture and as a substrate for the growth of aquatic plants and invertebrates which in turn are a source of nutrition to cultured species. In two separate tests AquaMats® were placed into raceways used to rear rainbow trout Oncorhynchus mykiss (Walbaum) to evaluate their effect on fish growth and fin condition. In the first test, the AquaMats® were placed perpendicular to the raceway length similar to a baffle design. One treatment consisted of AquaMats® that were cleaned on a regular basis, and the other treatment consisted of AquaMats® that were not cleaned throughout the test. By the end of the test no differences were found between treatments with respect to final fish weight, specific growth rate, or feed conversion ratio. The use of AquaMats® did not improve fin condition, in fact several fins measured were significantly better among control fish. In the second test AquaMats® were placed on the raceway bottom parallel to their length and to the water flow. AquaMats® were also hung from the side of the raceway to provide cover. At the conclusion of this test no differences were found between treatments with respect to final fish weight, specific growth rate, or feed conversion ratio. The placement of AquaMats® did have a transitory impact on fin condition. Mid‐way through the test, treatment fish generally exhibited longer fins compared with the controls. However, by the end of the test, these differences were no longer detectable. The results from both tests indicate that fish were not provided with additional nutrition to the extent it improved growth. However, the use of AquaMats® did make a significant, albeit transitory, impact on fin condition.     

Intestinal absorption and tissue distribution of glucose and isoleucine in rainbow trout (Oncorhynchus mykiss)

The intestinal absorption and tissue distribution of D(U¹⁴C)-glucose (¹⁴C-glc), 3-O-methyl-D(U¹⁴C)-glucose (¹⁴C-OMG) and L(U¹⁴C)-isoleucine (¹⁴C-ile) were studied in rainbow trout, Oncorhynchus mykiss, using a forced-feeding technique. The appearance of radioactivity in faeces, blood, liver, white muscle and brain was monitored over 48 h. The recoveries of radioactivity 48 h postfeeding in the fish tissues studied were 36, 57 and 48% for ¹⁴C-glc, ¹⁴C-ile and ¹⁴C-OMG, respectively. White muscle and liver contained most radioactivity on the whole tissue basis. Concentrations of ¹⁴C-glc and its derivatives in the liver and the brain exceeded those of ¹⁴C-ile and its derivatives, but the reverse was found in the white muscle. These differences may reflect differences in the metabolism of glucose and isoleucine. All tissues studied showed some differences in the accumulation of ¹⁴C originating from ¹⁴C-OMG and ¹⁴C-glc. As ¹⁴C-OMG is a nonmetabolizable glucose analogue, these differences may be the result of glucose metabolism at tissue level.     

Landscape‐level constraints on recruitment of chinook salmon (Oncorhynchus tshawytscha) in the Columbia River basin,USA

• 1. The decline of salmonid populations in the Pacific Northwest has been well‐documented. It is unclear, however, which threats to salmonid persistence are the most serious, and how best to prioritize recovery efforts intended to ameliorate these threats.
• 2. It has been argued previously that one possible cause of salmon endangerment is degradation of spawning grounds. In order to explore this hypothesis, this study examines the relationships between chinook salmon (Oncorhynchus tshawytscha) productivity and landscape‐level characteristics of spawning grounds in the interior Columbia River Basin.
• 3. Population productivity is expressed as the mean and maximum recruitment rates for different stocks, measured from 1980 to 1990; habitat conditions are calculated using sub‐watershed scale data on land cover, land use, water quality and watershed hydrology.
• 4. Significant linear regression results were obtained for three environmental variables: percentage of land classified as urban, proportion of stream length failing to meet water quality standards, and an index of the ability of streams to recover from sediment flow events. A multiple regression with all three variables accounts for over 60% of the variation in mean salmon recruitment.
• 5. It further appears that these landscape attributes may limit the maximum recruitment rates of salmon, with a magnitude of difference in productivity large enough to be relevant to recovery planners. Additional study will be necessary to identify cause‐and‐effect linkages between habitat quality and salmon recruitment success, and to determine the ultimate impact of changes in recruitment rates on short‐ and long‐term salmon population trajectories.

Copyright © 2002 John Wiley & Sons, Ltd.     

Distinct alpha (α)-subunits of salmon glycoprotein hormones: production sites in the pituitary with sexual maturity

Salmon pituitary glands contain two structurally distinct -subunit proteins (1 and 2) of glycoprotein hormones: the 2-subunit is common to all salmon gonadotropins (GTH I and GTH II), whereas the 1-subunit is present in only some GTH I molecules. GTH I is predominant in the pituitary gland and plasma during gametogenesis of salmon, but the roles of the 2 GTHs in gametogenesis remain unclear. To understand the roles of GTH I, it is important to clarify patterns of 1- and 2-subunit production with sexual maturity. Thus, we produced antisera that recognized the 1- or 2-subunit, and then immunohistochemically examined the production sites of these subunits in the trout pituitary gland during ovarian development. In all pituitary glands examined, the immunoreactivity of both the 1- and 2-subunits was strong in the GTH II-producing cells, although salmon GTH II, both 1- and II-subunits, has not been detected. However, GTH I-producing cells showed a less dense immunoreactivity for 1- and 2-subunits, whereas the I-subunit was abundant. On the other hand, TSH cells, reacted with 2 but not with 1.     

Seal predation on salmon and forage fish schools as a function of tidal currents in the San Juan Islands, Washington, USA

Tidal patterns in feeding behaviour are known in several upper trophic level predators. Although harbour seal ( Phoca vitulina richardsi ) movements between resting and foraging areas are often correlated with tidal phase, little is known about tidal influences on seal foraging because it is difficult to make direct observations of predation events. This study sought to determine whether harbour seals exhibit tidal patterns in their at-sea distribution, abundance, and foraging success and to discuss how changes in capture rates or prey types might affect the ability of an individual to meet its daily energy requirement. During 1995–97, seal abundance in the water during flooding tides was significantly greater than median daily abundance. Seals aggregated near a channel constriction. Salmon accounted for 50% and 87% of observed captures of single, large fish in 1996 and 1997, respectively. Predation on schooling fishes involved juvenile sandlance or herring. Large-fish captures were episodic (16.9% and 27.5% of observations with nonzero capture rates) and occurred more often on the incoming tide near constricted water flow. Median per capita capture rates were highest in currents during slower flooding (0.31 fish·seal^–1 h^–1). Surface attacks on forage fish schools were more common than large-fish captures (54.0% and 66.7% of observations with at least one attack on forage fish). Night-time and subsurface feeding were not assessed. Given what is known about seal food requirements, tidal differences in capture rates are predicted to have a significant impact on both the hunting strategy and energy intake of individuals. Results support the idea that interactions among tidal currents, topographic features, and fish play a role in structuring marine predator–prey dynamics.     

在循环养殖系统中不同溶氧量对虹鳟幼鱼代谢水平的影响

在循环养殖系统中设置四种溶氧水平,分别为7.05、8.82、11.84和15.80 mg/L,其中8.82 mg/L为对照组,对虹鳟幼鱼（体长13.0-18.5 cm）的代谢水平及生长率进行了研究。结果表明,饲养30 d后7.05mg/L的低溶氧使虹鳟幼鱼耗氧率和排氨率下降,11.84和15.80 mg/L溶氧下饲养的鱼耗氧率明显增加,15.80 mg/L使鱼的排氨率显著高于对照组。并且11.84和15.80 mg/L组虹鳟幼鱼在24 h内都具有高的代谢水平。随着溶氧量提高,虹鳟幼鱼的增重率、特定生长率和饲料转化率均随之升高,表现出生长指标的明显变化。     

添加氯化钾和蛋黄对虹鳟精液冷冻保存的效果

为筛选出更有效的虹鳟(Oncorhynchus mykiss)精液冷冻保存液,在以10％ 甲醇和0.3 M葡萄糖作为主要成分的基础上,分别或同时添加0.9 g/L氯化钾和10％ 蛋黄形成四种冷冻保存液,用于虹鳟精液冷冻保存试验,分别形成4个处理组:Ⅰ#(不添加氯化钾和蛋黄)、Ⅱ#(添加氯化钾)、Ⅲ#(添加蛋黄)和Ⅳ#(...     

Synergistic effect of sodium selenite and Pediococcus acidilactici on growth,intestinal bacterial counts,selenium bioavailability,hepatic enzymes and non‐specific immune response in rainbow trout (Oncorhynchus mykiss)

Lactic acid bacteria (LAB) have a crucial role in inorganic selenium metabolism as well as their known desirable effects on fish. In this study, the synergistic effects of dietary sodium selenite and Pediococcus acidilactici on growth performance, intestinal bacterial counts, selenium bioavailability, hepatic antioxidant enzyme thioredoxin reductase activity and hepatic glycolytic enzyme activity that is hexokinase, phosphofructokinase and pyruvate kinase, and non‐specific immune response such as serum lysozyme and complements C₃, C₄ and ACH₅₀ activity in rainbow trout (Oncorhynchus mykiss) were investigated. Thus, a 3 × 3 factorial design experiment was conducted with nine purified diets including three levels of sodium selenite (0, 1 and 2 mg/kg) and three levels of P. acidilactici (0, 7 and 9 log CFU/g). After 8 weeks of feeding, weight gain and specific growth rate were increased by increasing dietary sodium selenite and P. acidilactici levels compared to control (p < .05), whereas feed conversion ratio and condition factor was decreased by increasing dietary sodium selenite and P. acidilactici amounts in comparison with control (p < .05). Survival rate was not significantly affected among the experimental treatments (p > .05). Total cultivable bacterial populations after 4 and 8 weeks of the feeding trial were not significantly different among the dietary treatments, while LAB levels were higher in P. acidilactici‐fed groups than in control and selenium‐fed groups (p < .05). Selenocysteine, methylselenocysteine and selenomethionine levels in the intestine of rainbow trout were increased by increasing the sodium selenite and P. acidilactici levels (p < .05), and selenocysteine was found the most selenium species in the trout intestine. The quantity of total selenium in the whole body, intestine, blood, liver and muscle of rainbow trout were increased by increasing the amounts of sodium selenite and P. acidilactici compared to control (p < .05). Hepatic thioredoxin reductase and hexokinase activity were increased by increasing dietary selenium and P. acidilactici levels in comparison to control (p < .05), whereas phosphofructokinase and pyruvate kinase activity in the liver of rainbow trout were not significantly different between the dietary treatments. Serum lysozyme, complements C₃, C₄ and ACH₅₀ activity were enhanced by increasing dietary selenium and P. acidilactici levels compared to control (p < .05). The most synergistic effects of dietary supplements on growth and metabolism of rainbow trout were obtained at 2 mg/kg sodium selenite and 7 log CFU/g P. acidilactici. The findings revealed the synergistic effect of dietary selenium and P. acidilactici on growth and metabolism in rainbow trout (O. mykiss).     

Effect of an alcohol extract from a defatted soybean meal supplemented with a casein-based semi-purified diet on the biliary bile status and intestinal conditions in rainbow trout Oncorhynchus mykiss (Walbaum)

A feeding experiment was conducted to examine the effect of a supplemental ethanol extract from a defatted soybean meal on the biliary bile status and intestinal conditions of rainbow trout Oncorhynchus mykiss . A semi-purified control diet based on casein (Cont) and three diets supplemented with the extract (ES), bovine bile salts (BS) and their combination (ESBS) were fed to trout (10 g) for 6 weeks. The growth, feed efficiency ratio, fat digestibility and gallbladder- and hepato-somatic indices of fish fed diet ES decreased. Compared with this group, these parameters were improved in fish fed diet ESBS. The total biliary bile salt content was the lowest in fish fed diet ES and this group had a high proportion of chenodeoxycholyltaurine. The inclusion of the bile salts to diet ES (diet ESBS) increased the total biliary bile salt content. A similar trend was observed in the bile salt concentration of intestinal digesta. Although morphological changes occurred in epithelial cells of the distal intestine of fish fed diet ES, the histological features of fish fed diet ESBS were similar to those of fish fed diet Cont. These results indicate that alcohol-soluble substances of soybean meal cause physiological changes in the biliary bile and intestine of rainbow trout.     

Effect of gonadotropin type II and 17-hydroxy-4-pregnene-3,20-dione on 17,20β-dihydroxy-4-pregnen-3-one production by rainbow trout testes at different developmental stages

Plasma levels of 17,20-dihydroxy-4-pregnen-3-one (17,20OHP), which is involved in the regulation of spermiation in male salmonid fish, increase dramatically at the time of spermiation. To advance the understanding of the regulation of 17,20OHP production during the spermatogenetic cycle in trout, we have studied the in vitro effect of gonadotropin type II (GtH II) and the precursor 17-hydroxy-4-pregnene-3,20-dione (17OHP) on the production of 17,20OHP. The sensitivity with which testes secreted 17,20OHP following stimulation with GtH II was maximum during spermatogenesis. The addition of 17OHP (10 to 1600 ng ml-1) to the culture medium of testes fragments induced a significant and dose-related increase in 17,20OHP secretion. Although the capacity to produce 17,20OHP was not saturated by the 17OHP concentrations used, the conversion rate was highest for tested at an immature stage. As to the regulation of 17OHP, in vivo, a single injection of partially purified salmon gonadotropin (50 ng g-1 body weight) induced a significant increase in the circulating levels of 17OHP of immature males. In conclusion, the maximum sensitivity to GtH II stimulation and the highest conversion rate of 17OHP to 17,20OHP in vitro, occurred before the dramatic increase in the 17,20OHP secretion observed in rainbow trout at the time of spermiation.