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81.
Food availability and thermal regimes can largely govern growth opportunities in fishes. In temperate regions, streams can exhibit summer temperatures that exceed the optima for coolwater-adapted species relative to the amount of available food, and therefore, spring and fall may confer better growing conditions, especially for larger size classes. We examined the relationship between growth, consumption and growth efficiency across seasons in juvenile steelhead (Oncorhynchus mykiss) in their natal streams in Idaho, USA. Subyearling (0+) growth rates were higher in summer, whereas yearlings exhibited no statistically significant difference in growth between seasons. Consumption rates were overall lower in winter–spring but constituted a higher proportion of maximum consumption compared with summer and fall, indicating better food availability relative to metabolic demands. Net growth efficiencies were higher in winter–spring, but substantially more so than the proportion of maximum consumption. This suggests that overwinter growth performance was driven at least partly by higher growth efficiency, and the effect was most pronounced for yearling steelhead. The low proportions of maximum consumption for both age classes suggest that food was an overall limiting factor to growth, especially in summer when metabolic demands were highest. We discuss how temperature-based models can overestimate growth in the warmest parts of the year and develop a simple conceptual model for the seasonal timing of juvenile growth. In anadromous populations, the outmigration of presmolts in spring can reduce the level of competition. For the individuals that remain in the river, growth in this period can be particularly important. 相似文献
82.
Toxicity of Un-ionized Ammonia and High pH to Post-larval and Juvenile Freshwater Shrimp Macrobrachium rosenbergii 总被引:1,自引:0,他引:1
David L. Straus H. Randall Robinette John M. Heinen 《Journal of the World Aquaculture Society》1991,22(2):128-133
Post-larval and juvenile Macrobrachium rosenbergii were exposed for 72 h at 29 C to four pH levels (8.5, 9.0, 9.5, 10.0) and four concentrations of un-ionized ammonia-nitrogen (0, 1, 2, and 3 mg/L NHj -N). Results indicated potentiation between NH3 and high pH. Juveniles were more tolerant of high pH and NH3 than post-larvae.
For post-larvae, estimates of 72 h LC50 for pH were 9.43, 9.21, and 8.71 at 0, 1, and 2 mg/L NH3 -N, respectively; 72 h LC50 estimates for NH3 -N were 2.18 and 1.45 mg/L at pH levels of 8.5 and 9.0, respectively. For juveniles, estimates of 72 h LC50 for pH were 9.91, 9.56, 9.04, and 8.76 at 0, 1, 2, and 3 mg/L NH3 -N, respectively; 72 h LC50 estimates for NH3 -N were 2.02 and 0.54 mg/L at pH 9.0 and 9.5, respectively.
In pond culture of M. rosenbergii , high pH levels can cause mortality at stocking. The 72 h data can be used as an indication of safe stocking levels of pH and ammonia. These data suggest that post-larvae should not be exposed to pH > 9.0 nor to NH3 -N > 1 mg/L in the pH range 8.5–9.0 and juveniles should not be exposed to pH > 9.5 nor to NH3 -N > 0 mg/L at pH 9.5, > 1 mg/L at pH 9.0, or > 2 mg/L at pH 8.5. 相似文献
For post-larvae, estimates of 72 h LC50 for pH were 9.43, 9.21, and 8.71 at 0, 1, and 2 mg/L NH
In pond culture of M. rosenbergii , high pH levels can cause mortality at stocking. The 72 h data can be used as an indication of safe stocking levels of pH and ammonia. These data suggest that post-larvae should not be exposed to pH > 9.0 nor to NH
83.
García-Sánchez M. Pino González-Ávila Sergio Solana-Gutiérrez Joaquín Popa Marius Jurj Ramon Ionescu Georgeta Ionescu Ovidiu Fedorca Mihai Fedorca Ancuta 《Landscape Ecology》2022,37(5):1311-1329
Landscape Ecology - Romania is currently one of the best-connected landscapes, with high-quality habitats and a high density of brown bears. However, regional development measures are needed for... 相似文献