| Effects of environmental factors on growth and energy budget of yellow catfish Pelteobagrus fulvidraco (Richardson) was systematically investigated in the present study. The optimum bioenergetic feeding model and growth model of P. fulvidraco were established by the growth experiment. The research approach of population experiment of energy ecology was conducted to analyze the effect of ecological factors on biochemical composition, energy content, feeding, growth, food conversion efficiency and digestibility of yellow catfish, also to infer the effects of ecological factors such as feeding level, water temperature, body weight, dissolved oxygen level and ambient ammonia concentration on feeding, growth and energy allocation of tallow catfish. Furthermore, the effect of dissolved oxygen level on the blood parameters and the activities of main digestive enzymes of yellow catfish were studied. In addition, the effects of ambient ammonia concentration on the blood parameters and antioxidant capability of yellow catfish were investigated.1. The effect of feeding levels (FL,50%,60%,70%,80%,90% and 100% satiation per day) on growth, feeding and energy budget of juvenile yellow catfish with initial body weight 1.174±0.276 g were investigated during the 60 d rearing experiment. The results showed that the relationship between specific growth rate (SGR,% per day) of yellow catfish and feeding level was a decelerating curve, and the relationship was described as SGR=Y=a+b ln (FL+1). It was found that SGR, apparent digestibility coefficients (ADC,%), feed conversion efficiency (FCE,%) and growth energy was higher at 70% FL than other feeding level, and the faecal production was low in 70% FL, therefore, it was recommended that optimum feeding level for yellow catfish is 70% (corresponding to feeding ration 2.59%d-1) during this growth stage, which could save cost of formulated diet of artificial culture for yellow catfish and reduce the pollution.2. The effects of water temperature (21,24,27,30 and 33℃) and body weight (6,16 and 35 g) on maximum food consumption, specific growth rate and energy allocation of yellow catfish were investigated during 42 d rearing experiment in this study. Maximum food consumption, feeding ration, specific growth rate, food conversion efficiency and apparent digestibility were higher with temperature range from 24℃to 30℃than these in other water temperatures, as well as the allocation ratio of growth energy reached high level with temperature range from 24℃to 30℃. The optimum water temperature for growth was 27℃. Besides, the results showed that the body weight had significant impact on feeding and growth. Except for maximum food consumption and feeding ration, the other indexes of yellow catfish with 6 g and 16 g body weight were significantly higher than other individuals with 35 g, so body weight. Two way ANOVA analyses indicated that significant interactions effect of temperature and body weight on feeding and growth of yellow catfish.3. The effect of different concentrations of dissolved oxygen (2.28±0.56 mg l-1,4.04±0.38 mg l-1,6.51±0.64 mg l-1 and 9.11±1.62 mg l-1) on growth, energy metabolism and the activities of main digestive enzymes of yellow catfish with initial body weight 15.25±0.27 g were investigated during 56 d experiment. The results showed that:①Feeding, growth and food conversion efficiency increased with dissolved oxygen concentrations increasing, while no more increase were found when dissolved oxygen reaching 6.51±0.64 mg l-1 (saturation). Also, growth energy ratio accounting for assimilated energy increased significantly with dissolved oxygen increasing.②Except for pepsin and amylase in the stomach, the activities of protease, amylase and lipase in the liver and intestine, and lipase in stomach, increased with dissolved oxygen concentrations increasing.③Haemoglobin concentration (Hb) and red blood cell count (RBC) reduced with the level of dissolved oxygen increasing.4. The acute toxic test of ammonia nitrogen were conducted using four different sizes of yellow catfish (weighing 0.034±0.002 g,0.296±0.049 g,3.52±0.95 g and 32.96±5.75 g) by 96h low-hydrostatic method. The results showed that sensitivity of yellow catfish to ammonia nitrogen reduced with body weight increasing. Fish size and the 96-h LC50 of ammonia were significantly correlated.The effect of different concentrations of ambient ammonia nitrogen (0 (control),3.36, 6.72,13.44 and 26.88 mg l-1) on feeding, growth, blood parameters and antioxidative capability was studied using yellow catfish with body weight 20.24±0.18 g. The results showed that:①Feeding rate, specific growth rate, food conversion efficiency, apparent digestibility coefficients and growth energy proportion accounting for gross energy intake reduced with ammonia nitrogen concentrations increasing. Growth energy proportion accounting for gross energy intake of yellow catfish was about one fourth in the concentration of 26.88 mg l-1 ammonia nitrogen compared with the control group after 56 d rearing experiment.②Plasma cortisol level increased with ammonia nitrogen concentrations increasing, while blood glucose concentration reduced with ammonia nitrogen concentrations increasing. Linear relationship was found between plasma ammonia concentration and ambient ammonia nitrogen concentration, was and expressed as y=29.102x+89.089 (n=15, R2=0.9649). Ambient ammonia nitrogen concentration and plasma ammonia concentration were significantly correlated at the end of the experiment (P<0.05). Alanine transaminase (ALT), aspartate transaminase (AST) and alkaline phosphatase (AKP) in the plasma of yellow catfish increased, while serum total protein reduced, when exposure to high ammonia concentration. This result indicated that high ammonia concentration leading to liver damage, which possibly due to fish death after long time exposure to high ammonia concentration.③Certain threshold was found in the inductive effect of ammonia on the activities of antioxidative enzyme. Total antioxidative capacity (T-AOC), antioxidative enzyme activities (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX)) and glutathione (GSH) in the blood, liver and gill tissue of yellow catfish reduced, but maleie dialdehyde concentration (MDA) increased in all above three tissues, with ammonia nitrogen concentration increasing.5. The best feeding and growth model of bioenergetics in yellow catfish was established according to the results from the second, third, fourth and fifth chapters. The bioenergetics model included the following sub-models: Body energy content:lnE=0.1779×T+0.8376×lnW-0.0036×T2+0.0053×T×lnWMaximum food consumption: lnCmax=-0.1998×T+0.3799×lnW+0.0025×T2+0.0206×T×lnWFaecal production:F=(0.2847 FR-0.2434)DO0.2278Excretion energy:U=0.0354 FR DO0.4056 e-0.0059TANMetabolism energy:R=(0.0452 FR+0.2680) DO0.4319 e-0.0096TANAccording to test the degree of accuracy of above models, these models showed good prediction to feeding rate. The predicted value of final body weight from the present models agreed well with the observed value of the group with the body weight 16 g at different water temperatures. Also, the predicted value of final body weight from the present models agreed well with the observed value of the groups with 2.28±0.56 mg l-1 and 4.04±0.38 mg l-1 dissolved oxygen. But the predicted value of final body weight from the present models disagreed with the observed value of yellow catfish exposure to different levels of ammonia nitrogen. |
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