Antinutritive effects of galactomannan-rich endosperm of Sesbania (Sesbania aculeata) seeds on growth and feed utilization in tilapia, Oreochromis niloticus

An 8‐week feeding trial was conducted using tilapia, Oreochromis niloticus L., in a recirculation system maintained at 27±0.2°C to observe the negative effects of Sesbania endosperm on growth and nutrient utilization. Five experimental diets were formulated to contain 32% protein, of which fishmeal was the major source. Endosperm separated from Sesbania seeds was included at levels of 0.0%, 2.9%, 5.8%, 8.7% and 11.6% in diets 1 (control), 2, 3, 4 and 5, respectively, equivalent to levels of 0.0%, 9.7%, 19.4%, 29.1% and 38.8%, respectively, of whole Sesbania seeds. Each treatment had two replicates, eight fish per replicate, with a mean initial live weight of 5.2±0.1 g. Fish were fed 20 g per kg metabolic body weight of fish daily. The body weight gain, metabolic growth rate, feed conversion ratio, protein efficiency ratio, protein productive value and energy retention of fish fed the control and diet 2 were significantly better (P<0.05) than those of fish fed the other diets. Physical observation showed that the intestines of the fish fed diets that included endosperm contained loose, viscous and sticky material. Fish fed diets 3, 4 and 5 had a lower proportion of dry matter in their faeces, and lower apparent crude lipid and energy digestibility coefficients compared with fish fed the control diet and diet 2. They also had significantly reduced levels of muscle and plasma cholesterol, whole‐body crude protein, lipid and gross energy.     

Nutritional evaluation of Tenebrio molitor meal as fishmeal substitute for tilapia (Oreochromis niloticus) diet

Fishmeal (FM) and soy meal (SM) are the most common protein sources used in fish feed, but they are associated with environmental, economic or production problems. Insects could be an interesting alternative source of protein. This work investigates the nutritive value of Tenebrio molitor meal (TM) and the effect of total replacement of SM by TM (TM/FM diet) or partial replacement of FM by TM (TM/FM/SM diet) versus a diet based in SM and FM (FM/SM diet) for tilapia. We studied the chitin content in TM, the in vitro protein digestibility, protease activity, oxidative stress and antioxidant defences, growth performance and nutrient utilization. The results indicate that an inclusion up to 500 g kg^?1 of TM in the diet did not affect feed intake, in vitro protein digestibility, muscle amino acid composition or biometric indexes. However, their inclusion reduced growth performance and affected the muscle fatty acid profile. The lowest values for protease activity, elevated FRAP in digestive tracts and ROS level in muscle and higher SOD activity were observed in fish fed with SM/FM diet. The use of TM requires better understanding of the role of chitin in digestion and the study of toxins that might affect fish growth.     

Evaluation of pea protein isolate as alternative protein source in diets for juvenile tilapia (Oreochromis niloticus)

To evaluate isolated pea protein as feed ingredient for tilapia (Oreochromis niloticus) juveniles, triplicate groups were fed with four isonitrogenous [crude protein: 421.1–427.5 g kg⁻¹ in dry matter (d.m.)] and isoenergetic (gross energy: 20.46–21.06 MJ kg⁻¹ d.m.) diets with varying protein sources for 8 weeks. Fish meal-based protein content of diets was substituted with 0% (diet 100/0=control group), 30% (diet 70/30), 45% (diet 55/45) and 60% (diet 40/60) isolated pea protein. Tilapia juveniles with an initial body weight of 2.23–2.27 g were fed in average at a level of 5% of their body weight per day. Highest individual weight gain (WG: 21.39 g) and specific growth rate (SGR: 4.21% day⁻¹) and best feed conversion ratio (FCR: 0.90) were observed in tilapia fed diet 100/0, followed by fish-fed diet 70/30 (WG: 19.09 g; SGR: 4.03% day⁻¹; FCR: 0.98), diet 55/45 (WG: 16.69 g; SGR: 3.80% day⁻¹; FCR: 1.06) and diet 40/60 (WG: 16.18 g; SGR: 3.74% day⁻¹; FCR: 1.06). Although fish fed diet 100/0 showed the best performance, inclusion of 30% protein derived from pea protein isolate resulted in a growth performance (in terms of WG and SGR) that did not differ significantly from diet 100/0 in contrast to fish fed diet 55/45 and 40/60. Crude ash content in the final body composition of the experimental fish decreased with increasing dietary pea protein content, while crude protein and lipid content remained equal between the groups. Significant decreasing growth performance and body ash incorporation of tilapia at higher inclusion levels seem to be mainly related to the dietary amino acid profile and phytic acid contents.     

Evaluation of hydrolysed rubber seed meal as a dietary protein source for Nile tilapia Oreochromis niloticus L.

This study evaluated the use of hydrolysed rubber seed meal as a locally grown alternative feed ingredient to reduce the use of fishmeal within formulated feeds for tilapia. Five experimental diets were prepared by formulating different inclusion levels of hydrolysed rubber seed meal (0%, 25%, 50%, 75% and 100% of plant‐based protein contribution). Dried and defatted rubber seed meal was hydrolysed by adding rumen digesta liquid to the ingredient. For digestibility measurement, chromic oxide was added to each diet as an inert marker. The digestibility trial was conducted over a 14‐day period by collecting faecal matter from the rearing tanks. In addition, a growth trial was conducted over a period of 50 days using four replicates per dietary treatment. In both experiments, all fish were fed three times daily to apparent satiation. At the end of growth trial, the inclusion level of hydrolysed rubber seed meal up to 50% of plant‐based protein contribution did not give any significant difference compared to the control diet in terms of feed efficiency, specific growth rate and protein retention parameters. In the digestibility study, fish fed diets containing hydrolysed rubber seed meal up to a 50% of plant‐based protein inclusion level did not give any significant difference compared to the control diet in terms of protein and dry matter apparent digestibility. Based on the result of this growth and digestibility study, up to a 50% of plant‐based protein contribution of hydrolysed rubber seed meal can be used within formulated tilapia feeds without any adverse effect.     

Juvenile tilapia (Oreochromis niloticus×Oreochromis aureus) requires dietary myo-inositol for maximal growth

An 8-week growth experiment was conducted to estimate the dietary requirement of myo-inositol (MI) for juvenile hybrid tilapia. MI was supplemented at 0, 150, 250, 350, 450, 600, and 1200 mg/kg diet in the basal diet providing 0, 167, 259, 367, 479, 612, and 1253 mg MI/kg diet. Basal diet without MI but with succinylsulfathiazole to suppress MI synthesis by intestinal bacteria was included for comparison. Each diet was fed to triplicate groups of tilapia (mean initial weight 0.51±0.01 g, n=3). Fish fed ≥367 mg MI/kg diet had significantly (P<0.05) higher weight gain, followed by fish fed 259 mg MI/kg diet, and lowest for fish fed the unsupplemented basal diet. Fish fed ≥367 mg MI/kg diet had higher feed efficiency than fish fed the basal diet. Supplementation of dietary inositol did not affect survival of tilapia. The MI concentrations in liver were highest in fish fed the ≥479 mg MI/kg diet, followed by fish fed the 259 and 167 mg MI/kg diets, and lowest in fish fed the basal diet. Hepatic lipid concentrations were higher in fish fed 367 mg MI/kg diet than fish fed ≤259 mg MI/kg diet. Weight gain percentage and MI concentrations in the liver for the different treatments were analyzed by broken-line regression and indicated that the requirement for dietary MI in growing tilapia is about 400 mg/kg diet. Addition of an antibiotic to basal diet did not affect the growth and hepatic inositol concentration of tilapia, suggesting that the intestinal microbial synthesis was not a significant source of inositol for tilapia.     

Replacing dietary corn with barley seeds in Nile tilapia, Oreochromis niloticus (L.), feed

Four isocaloric–isonitrogenous rations containing 0%, 15%, 30% and 51% of ground barley seeds as a replacement for dietary corn were fed to three replicate groups of Oreochromis niloticus (Linnaeus) fingerlings with a mean initial weight of 3.5 g. The randomly selected fish were tested for 9 weeks in 60 L circular tanks. Each tank was considered as an experimental unit. The tanks were put together in a water recirculating system using filtered and aerated ground well water (24 ± 3 °C). Tilapia weight gain, feed conversion, specific growth rate and protein efficiency ratio were similar in fish fed diets containing 15% and 30% barley and were superior to those fed diets containing 0% control and 51% barley. There were no differences between tilapia fed diets containing 0% and 51% barley. Body moisture, crude fat, crude protein and total ash did not change as the level of barley in the feeds was increased.     

Immuomodulatory effect of dietary turmeric supplementation on Nile tilapia (Oreochromis niloticus)

This study aimed to assess the immunomodulatory effect of dietary turmeric (TUM) in Oreochromis niloticus juveniles. A total of 240 Oreochromis niloticus fingerlings were divided into four equal groups (n = 60), three replicates (n = 20) for each: control and TUM‐treated groups at 2 (T1), 4 (T2) and 8 (T3) g kg^?1 diets for 8 weeks. Body weight gain, leucocytes counts, plasma levels of interleukin 2 (IL‐2), interleukin 4 (IL‐4), lymphocyte proliferation index to pokeweed mitogen (PWM), nitric oxide (NO) and lysozyme enzyme activities were measured. Histopathology of spleen was performed. TUM at 2 g kg^?1 significantly (p < .05) improved weight gain, leucocytes, NO and lysozyme activity than control and other treatment groups. IL‐2 level was significantly lower (p < .05) in T2 and T3 than in control and T1, while IL‐4 and lymphocyte proliferation index were significantly (p < .05) elevated in T3 than control, T1 and T2. Spleens of T2 showed improvement in white pulp, while spleen of T3 and T4 revealed white pulp depletion. In conclusion, TUM supplementation exerted immunomodulatory effect in Oreochromis niloticus through manipulation of lymphocyte count, IL‐2, IL‐4 and antibacterial enzymatic activity (NO and lysozyme) that resulted in higher weight gain. Increasing TUM supplementation of fish diets beyond 2 g kg^?1 was not beneficial.     

Dry whey meal as a protein source in practical diets for Nile tilapia,Oreochromis niloticus fingerlings

ABSTRACT

This study was conducted as a trial of using dry whey meal (DWM) as a substitute for fish meal (FM) in practical diets for Nile tilapia, Oreochromis niloticus. Triplicate fish groups were fed on five isonitrogenous (30.2%) and isolipidic (6.9%) diets. The control diet (D1) used FM as the sole protein source. In the other four diets (D2–D5), FM protein was substituted by 25, 50, 75, or 100% DWM. Fish (3.5 ± 0.1 g) were stocked at a rate of 20 fish per 100-L aquarium and fed one of the tested diets up to satiation twice daily for 12 weeks. Fish growth, feed utilization, protein efficiency ratio, apparent protein utilization, and energy utilization for fish fed DWM diets up to 75% FM (D2–D4) tended to be higher but were not statistically different than the control diet. No significant effect of diet was found in whole-body moisture, crude protein, and total ash contents. Whole-body lipid content in fish fed the 100% DWM (D5) diet was significantly higher than that for fish fed the control diet. The optimal replacement level of FM by DWM was estimated by second-order polynomial regression to be 62.5%.     

Evaluation of guar seed as a protein source in Nile tilapia, Oreochromis niloticus (L.), practical diets

An 84-day feeding trial was conducted with juvenile (6.9 g) Nile tilapia, Oreochromis niloticus (L.), to investigate the effects of replacing fish meal with the legume guar seed as a protein source in practical diets. Four isonitrogenous (32% crude protein) and isocaloric (3.5kcal DEg^?1 diet) diets were formulated. The replacement levels for guar were 25%, 50% and 75%. The reference diet contained fish meal as the main protein source and no guar. The growth performance, feed conversion ratio and protein efficiency ratio were significantly better in fish fed diets with 25%, 50% and 0% guar than in fish fed the 75% guar diet. The results of the present study suggest that effective replacement of fish meal protein by guar seed protein up to the level of 50% is possible in tilapia practical diets without any adverse effects on growth and feed conversion ratio.     

Meat and bone meal as a potential source of phosphorus in plant-protein-based diets for Nile tilapia (Oreochromis niloticus)

A growth trial was conducted to evaluate meat and bone meal (MBM) as a source of Phosphorus (P) for Nile tilapia fed with plant-based diets on growth, and the efficiency of P utilization. Four isonitrogenous and isoenergetic diets were formulated. A plant-based diet, deficient in P (0.45 % diet, no P added), was used as the basal diet. Three levels of MBM were substituted for cornstarch in the base diet to produce experimental diets containing MBM_0.56, MBM_0.67, or MBM_0.78% P. These diets were fed (to apparent satiation) to Nile tilapia (initial body weight = 1.53 ± 0.01 g) for eight weeks. Weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR, feed:gain), whole-body P concentration (WBPC), protein retention (PR), and retained phosphorus (RP) increased significantly (P ≤ 0.05), with the increasing dietary P levels coming from MBM. Diets containing MBM_0.78 produced significantly greater WG, SGR, WBPC, PR, and RP compared to other experimental diets (P ≤ 0.05). The linear regression analysis revealed a positive correlation between the WG, WBPC, RP, and dietary P levels coming from MBM of Nile tilapia. These results indicate that MBM has an additional value as a source of P and can serve as a potential source of supplemental P for Nile tilapia fed plant-protein-based diets.     

Utilization of Caridina nilotica (Roux) meal as a protein ingredient in feeds for Nile tilapia (Oreochromis niloticus)

The effects of replacing fish meal with Caridina nilotica as a protein ingredient on growth performance, nutrient utilization, carcass, proximate composition and economic benefits in Nile tilapia (Oreochromis niloticus) culture was evaluated. Replacement of the FM with C. nilotica was done at 25%, 50%, 75% and 100% (D25, D50, D75 and D100) and the substitution effects was compared with the control diet (D0, 0% C. nilotica). After 140 days of culture, the best growth performance, nutrient utilization and economic benefits occurred in fish groups fed diets with 25% C. nilotica inclusion. However, growth performance in fish fed diets D50 and D75 were comparable with the control (P > 0.05). At 100% substitution level of FM with C. nilotica, the growth performance and fish survival was lower than control. Protein and lipid contents in the fish and their digestibilities were highest in diet D25 and decreased with increasing levels of substitution of FM with C. nilotica. This study demonstrate that utilization of local protein sources (C. nilotica) can be effectively used to replace up to 75% of FM in the diets without compromising growth performance, survival, nutrient utilization and economic benefits in O. niloticus culture.     

尼罗罗非鱼幼鱼饲料的适宜脂肪需要

选用初始体质量为(46.14±4.67)g的尼罗罗非鱼(Oreochromis nilotica)360尾,随机分成6组(每组4重复,每重复15尾),分别饲喂添加鱼油水平为0%(对照组)、3%、6%、9%、12%和15%的纯化饲料(实测脂肪水平为0.20%、2.70%、6.11%、8.04%、11.13%和14.85%)。饲养8周后,以尼罗罗非鱼幼鱼的生长、体组成、血清生化及脂肪代谢酶活性等指标为判断依据,确定其饲料的脂肪需要量。结果表明,随饲料脂肪水平的升高,尼罗罗非鱼的增重率、特定生长率以及蛋白质效率均呈现先上升后下降的趋势,饲料系数呈现先下降后上升的趋势。饲料脂肪水平的升高使尼罗罗非鱼肝体比及全鱼和肌肉的脂肪含量显著增加(P<0.05)。随饲料脂肪水平的升高,尼罗罗非鱼血清总胆固醇和甘油三酯含量呈先上升后下降的趋势,各实验组显著高于对照组(P<0.05);血清高密度脂蛋白含量呈先上升后稳定的趋势;血清谷丙转氨酶和谷草转氨酶活性均在饲料脂肪水平为6.11%时最小,在14.85%时达到最大。随饲料脂肪水平的升高,尼罗罗非鱼脂蛋白酯酶、肝脂酶和肠道脂肪酶活性均呈先升高后下降的趋势,脂肪酸合成酶活性显著下降(P<0.05)。对增重率、蛋白质效率、饲料系数和血清高密度脂蛋白胆固醇进行回归分析得出,尼罗罗非鱼幼鱼饲料最适脂肪水平分别为8.86%,9.75%,9.40%和8.30%,因此确定尼罗罗非鱼幼鱼饲料适宜的脂肪需要量为8.30%～9.75%。     

Susceptibility of Nile tilapia (Oreochromis niloticus) fed with dietary sodium chloride to nitrite toxicity

Juvenile Nile tilapia (Oreochromis niloticus) were fed with diets supplemented with 0 or 6% NaCl for 10 weeks. Tilapia were exposed to approximately 21 mg/l nitrite-N after 5 and 10 weeks of feeding to determine the effect of dietary NaCl supplementation on resistance to nitrite toxicity. Fish were sampled before (baseline, pre-exposure) and after 24 h nitrite exposure to determine the effects of dietary NaCl on mortality, hematology (hematocrit, hemoglobin, and methemoglobin), and plasma electrolyte dynamics (nitrite, chloride, sodium, and potassium). After 10 weeks of feeding, tilapia were also challenged with Streptococcus iniae to determine the effect of sodium chloride on immunity. Tilapia fed with the NaCl-supplemented diet had significantly higher weight gain compared with the control group, which was associated with a significant increase in feed intake in the NaCl group. Mortality from nitrite exposure was lower in tilapia fed with the NaCl-supplemented diet compared with the control group at 5 and 10 weeks, but the differences were not significant. However, dietary NaCl supplementation caused a significant decrease in plasma nitrite levels after nitrite exposure. The dietary reduction in nitrite may be related to the increase in plasma chloride in the 6% NaCl-supplemented fish. A direct link between the effects of dietary NaCl supplementation on methemoglobin (MetHb) could not be established. Tilapia in this study were subjected to acute nitrite toxicity. Dietary sodium chloride may be more effective in protecting against nitrite toxicity at lower levels of nitrite, but the conditions at which it proves to be effective may be limited and requires further investigation. Feeding NaCl to tilapia did not affect susceptibility to S. iniae or immune function, but nitrite exposure cause a stress-related reduction in non-specific immune function. This is the first study to examine the effects of dietary salt on nitrite toxicity in tilapia.     

Tol2-mediated transgenesis in tilapia (Oreochromis niloticus)

The Nile tilapia (Oreochromis niloticus) is an important species in aquaculture and an excellent model system for laboratory studies. Functional genetic analysis using this species has been difficult because existing methods for producing transgenics are inefficient. Here we show that the Tol2 transposon system can be used to create transgenic tilapia with high efficiency. We constructed a line that is transgenic for GFP under control of a Xenopus elongation factor 1α (EF1α) promoter. The germline transmission rate of the Tol2 construct to the first generation was about 30%, which is much higher than conventional methods. GFP expression was strong and ubiquitous in the embryos. Application of the Tol2 system for constructing transgenics in tilapia and related species will promote research in many areas, but will be especially useful for studies of evolutionary developmental biology in the cichlid fishes of East Africa.     

Effect of dietary protein level on the reproductive performance of Nile tilapia, Oreochromis niloticus (L.)

The effects of five dietary protein levels (25%, 30%, 35%, 40% and 45%) on the individual spawning frequency and the egg production of 135 tagged female Nile tilapia, Oreochromis niloticus (L.), were studied from 8 May to 19 November 1996 in outdoor concrete tanks. Virtually identical spawning patterns were found in all treatments, but there was a great deal of variation in the frequency of spawning and egg production. Overall, individual spawning frequency varied from one to 14 and individual egg production from 31 to 2828 eggs per spawning. The average number of spawnings and average number of eggs per spawning for fish receiving dietary protein levels of 25%, 30%, 35%, 40% and 45% were 8.0 ±1.6, 8.4 ± 2.2, 8.5 ± 2.7, 8.4 ± 2.5 and 9.4 ± 2.1 spawnings, and 1167 ± 305, 1082 ± 410, 1288 ± 324, 1145 ± 389 and 1328 ± 311 eggs per spawning, respectively. Fish receiving 45% dietary protein spawned more frequently than fish receiving 25% dietary protein. The total number of eggs produced per female was significantly higher for females fed 45% protein feed than females receiving 25% and 30% protein feeds. No definite trend was found in the number of eggs produced per spawning and the number of eggs produced per gram in females fed at different protein levels. Based on weekly checking, the time interval between spawnings varied from 7 to 77 days, and mean spawning intervals ranged from 15.8 to 17.1 days. Sixty per cent of females spawned after an interval 14 days, 15% after 21 days, 13.6% after 7 days, 7.2% after 28 days, 1.8% after 35 days and 1.0% after 42 days, and the time interval was 49-77 days for the rest of the females (1.5%). In all treatments, maximum spawning activity was recorded from May to August, and thereafter, it gradually decreased and no spawning females were found in November.     

The potential for rice wine residual as an alternative protein source in a practical diet for Nile tilapia (Oreochromis niloticus) at the juvenile stage

This study investigated the utilization level of rice wine residual (RWS) in a diet for juvenile Nile tilapia. The effects of RWS in diets were evaluated for growth (at week 4), fillet composition, haematological and blood chemical parameters (at weeks 3 and 6) and intestinal morphology (at week 6). The dietary treatments (each diet in triplicate groups) consisted of seven isonitrogenous (320 g kg^?1 crude protein) servings that were formulated to include RWS at levels of 0 (control diet), 75, 150, 225, 300, 375 and 450 g kg^?1 dry diet (Diets 1–7, respectively) and a commercial diet (Diet 8). The growth performances of fish in the groups on Diets 1–4 did not differ significantly. There were no marked variations in fillet composition, serum lysozyme, haematological profiles and blood urea nitrogen (BUN) among treatment diets, except for haematocrit and BUN (week 3) and haemoglobin (week 6) of fish on Diets 6–7. While the blood glucose increased as the amount of RWS incorporation increased (P < 0.05), the cholesterol decreased (P < 0.05). Only intestinal morphometry of fish fed Diet 7 differed significantly from any of the other treatments. Taken together, RWS (at 225 g kg^?1 diet) has the potential for use in juvenile Nile tilapia diet without negative effects.     

吉富罗非鱼成鱼胆碱的最适需要量

选用初始体质量为(220.00±8.34) g的吉富罗非鱼(Oreochromis niloticus)360尾, 随机分成6组,每组3重复(每重复20尾), 于1 m×1 m×1.5 m池塘网箱中饲养。分别饲喂胆碱含量为97.80(对照组)、375.04、565.74、974.27、      1 409.81、1 824.35 mg/kg的半纯化饲料10周, 研究胆碱对吉富罗非鱼成鱼生长、饲料利用、鱼体营养组成、胆碱蓄积量及部分血液生化指标的影响。结果显示, 经过10周的饲喂, 饲料中添加胆碱可显著提高鱼体增重率、特定生长率和饲料效率(P<0.05); 降低肝脂肪含量(P<0.05), 提高肌肉脂肪含量(P<0.05); 显著升高肝胆碱蓄积量(P<0.05); 胆碱添加组血清甘油三酯(TG)和总胆固醇(T-CHO)显著高于对照组(P<0.05), 并随饲料胆碱含量增加呈现升高的趋势; 肝甘油三酯(TG)和总胆固醇(T-CHO)随着胆碱含量的增加而显著降低(P<0.05); 血清谷草转氨酶(ALT)、谷丙转氨酶(AST)和碱性磷酸酶(ALP)均随着饲料胆碱含量的增大而显著降低(P<0.05)。结果表明, 饲料中添加适量的胆碱可以改善吉富罗非鱼成鱼的生长性能, 提高饲料利用效率, 降低肝脂肪含量, 促进肝脂肪转运; 对特定生长率进行回归分析, 得出吉富罗非鱼成鱼对饲料中胆碱的最低需要量为506.43 mg/kg, 而对肝胆碱蓄积量回归分析得出的需要量为981.38 mg/kg。

     

Toxicity and absorption of dietary leucomalachite green in Nile tilapia Oreochromis niloticus

Farmed fish are exposed to risks from feed-borne chemical contamination, such as leucomalachite green (LMG) in fish meal. Consequently, the use of malachite green is prohibited in aquacultural practice. An improved understanding of the toxicity of dietary LMG provided to farmed fish is needed in order to manage risk. Oreochromis niloticus specimens were fed experimental diets containing 0, 100, 500, and 2500 μg/kg LMG for 28 days. On sampling days 7, 14, and 28, fish in the exposed groups had detectable levels of LMG. Accumulation levels were approximately 12.2 % (in the liver) and 6.2 % (in the muscle) of the LMG concentration in the feed (104, 510, and 2200 μg/kg). Hematocrit and mean corpuscular hemoglobin concentrations in the 500 and 2500 μg/kg groups were significantly elevated at 7 and 14 days. Hemoglobin in the group that received the highest dose was significantly higher than that in the control group. Significant increases in the activities of alanine aminotransferase and alkaline phosphatase were also detected in the group receiving the highest dose. Total cholesterol concentrations in all of the exposed groups were significantly higher than those in the control group. These observations of toxicity were dose dependent. Histological changes in gills and livers were observed in LMG-exposed fish.     

吉富罗非鱼生长过程中氮收支变化的研究

为充实有关鱼类研究数据,提供实际生产理论依据,研究了吉富品系尼罗罗非鱼（Oreochromis niloticus）从鱼种（18 g）生长至成鱼（180 g）过程中氮收支变化。试验为期73 d,每日饱食投喂并收集鱼粪,溶解氧质量浓度为8.0-6.0 mg·L-1,pH为 7.5-6.5,水温为24-30 ℃。在鱼均质量达到50 g、100 g和180 g时测定并计算当前生长阶段氮收支。结果表明,生长氮比例在养殖初期最高（64%）,养殖中期最低（47%）;粪氮比例在养殖中期最高（9%）,养殖初期和末期分别为5%和4%;排泄氮比例随鱼的生长而逐渐增加。此外,试验期间水中总氮增加速度在养殖中期减慢,养殖末期再次加快。     

Digestive enzyme activity in juvenile Nile tilapia (Oreochromis niloticus, L) submitted to different dietary levels of shrimp protein hydrolysate

The effect of different dietary concentrations of shrimp protein hydrolysate (SPH) on digestive enzyme activity of Nile tilapia juveniles was evaluated. SPH concentrations in diets were 0, 15, 30 and 60 g kg^?1 (treatments SPH0, SPH15, SPH30 and SPH60, respectively). Hemoglobin, azocasein, BApNA (Nα-benzoyl-dl-arginine-p-nitroanilide), SApNA (Suc-Ala-Ala-Pro-Phe p-nitroanilide), aminoacyl of β-naphthylamide and starch were used as substrates for enzyme activity determinations. The activity of total alkaline protease was significantly higher (P < 0.05) in fish under SPH15 and SPH60 treatments than in the control (SPH0). However, the effect was not dose-dependent. Substrate-SDS-PAGE was also performed to evaluate changes in the profile of Nile tilapia digestive proteases caused by SPH. Substrate-SDS-PAGE revealed 12 active proteolytic bands, eight of which responded to SPH dietary incorporation. Inhibition substrate-SDS-PAGE indicated a decrease in the activity of three enzymes, with trypsin activity decreasing with the increase of SPH concentration, whereas the opposite occurred for two aminopeptidases. Distinct protease profiles were also found for each treatment, suggesting adaptability of digestive proteases from Nile tilapia to the different diets.