Effect of dietary high amount of calcium and phosphorous on reducing the prevalence of morphological deformities in GH-transgenic Nile tilapia

To satisfy the world’s growing need for animal protein, it is important to develop or select fish species which are suitable for optimal cultivation in closed recirculating aquaculture systems (CRASs) as an environment-friendly aquaculture technology for providing safe and secure aquaculture food products. We have developed an ‘all fish’ growth-hormone (GH)-transgenic Nile tilapia Oreochromis niloticus (GHTi) which appears to be a predominant candidate for CRAS since it has been found to exhibit two important characteristics, namely, a shorter rearing duration to a market size and lowered N and P discharge load. However, these fish have undergone morphological changes, resulting in a short body which is less acceptable to consumers as an edible fish. One possible solution to reducing the prevalence of such morphological deformities is to determine the association between changes in the nutritional conditions of these fish. To this end, we first calculated the ideal total calcium (Ca) and phosphorous (P) intake (g/kg), ideal daily Ca and P intake and retention (g/kg/day) and ideal daily feeding rate (%) for the fourth filial (F₄) offspring of GHTi. Our hypothesis was that GHTi would achieve the same total retention of Ca (14.6 g/kg) or P (7.69 g/kg) during a 69-day shorter rearing period as their production-matched pedigree common domestic strain (CTi). We estimated that when GHTi were fed conventional commercial diets to satiety, those with a body weight (BW) of more than approximately 230 g could not retain sufficient Ca, while those with a BW of more than approximately 429 g could not retain sufficient P. We then attempted to reduce the prevalence of morphological deformities in GHTi via dietary compound regulation by supplying a high amount of dietary Ca [6.82 % in the diet with Ca supplementation (Ca-S)] or P [4.75 % in the diet with P supplementation (P-S)]. Both the Ca-S and P-S diet improved mineral retention, while those fed on a Ca-S diet showed a lower prevalence of deformities, close to the size-matched CTi. These results suggest that the requirements of dietary Ca and P were significantly higher in GHTi than in CTi and, consequently, that the conventional levels of Ca and P in commercial diets for CTi cannot meet the mineral requirement of GHTi. We therefore propose to develop an optimal feed to meet the altered nutritional requirements of GH-transgenic Nile tilapia for growth-promoting optimization. This may become prerequisite for rearing this GHTi line in CRASs.     

Effect of dietary phosphorus supplementation on utilization of algae in the grow‐out diet of Nile tilapia Oreochromis niloticus

This research involved testing the replacement of corn gluten protein concentrate in the diet of 1.5 g Nile tilapia with biofuel algae‐based or algae supplemented with phosphorus diets. Experimental diets were formulated to replace 50% of the gluten meal protein in the control diet with biofuel algae protein (Alga50) or Spirulina (Spirulina50) protein. In addition, dicalcium phosphate (P) was added to the Alga50 at a concentration of 3.8% or 7.74% to mitigate aluminium (Al) toxicity and designated as Alga50 + P, and Alga50 + PP respectively. After 9 weeks of the feeding experiment, fish fed diets supplemented with P, Alga50 + P and Alga50 + PP differed significantly (P < 0.05) with respect to the feed conversion and protein deposition from the control. The mineral composition of the fish body showed a decrease in levels of Al and iron (Fe) due to the P supplements. The mineral composition of the faeces indicated that Al and Fe were excreted in the faeces and were not accumulated in the fish body. The effect of dicalcium P supplementation on the neutralization of Al in the diet resulted in improved fish growth and histological integrity of the gastrointestinal tract.     

Effect of dietary carbohydrate to lipid ratio on performance of Nile tilapia and enhancement of natural food in pond aquaculture

This study tested the effect of two diets differing in carbohydrate to lipid (CHO:LIP) ratio (4.7 vs. 19.5 g/g) on the contribution of natural food and the total fish production in tilapia ponds. Eight ponds, each divided into three equally sized compartments, were assigned to one of the two diets, which differed in CHO:LIP ratio but had the same digestible protein to digestible energy (DP:DE) ratio (15.5 and 15.6 g/MJ). Ponds were fed equal amounts of crude protein. Three feeding levels (no, low and high) were nested in each pond in a split plot design. Average body weight of fish at stocking was 90 g, and the duration of the experiment was 42 days. Increasing the CHO:LIP ratio had no impact on tilapia production. However, the feeding level influenced both biomass gain, specific growth rate and survival. The apparent digestibility coefficient (ADC) for fat and carbohydrate was influenced by dietary CHO:LIP ratio but ADC for energy was unaffected. Proximate analysis of fish body composition showed no effect of diet except for levels of ash. Diet had no effect on the organic matter composition of the faeces, and the contribution of natural food to fish nitrogen gain. Therefore, we postulate that changing the dietary non‐protein energy source from lipid to carbohydrate does not have any impact on tilapia culture in semi‐intensive ponds.     

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.     

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.     

Effect of dietary cyanobacteria on growth and accumulation of microcystins in Nile tilapia (Oreochromis niloticus)

A 12-week growth trial was conducted in a flow-through system to investigate the chronic toxic effect of dietary intake of cyanobacteria on growth, feed utilization and microcystins accumulation in Nile tilapia (Oreochromis niloticus L.) (initial body weight: 5.6 g). Six isonitrogenous and isocaloric diets were formulated to include different contents of cyanobacteria with the dietary microcystins increasing from 0 to 5460.06 ng/g diet. The results showed that dietary intake of cyanobacteria could increase the growth of tilapia while there are no impacts on feed conversion efficiency or mortality. Feeding rate was higher for the diets containing highest cyanobacteria. Microcystins were mostly accumulated in fish liver. The relationship between microcystins contents in muscle, liver, spleen and dietary intake could be described by quadratic equations.Microcystins content in the muscle of Nile tilapia in present study exceeded the upper limit of the tolerable daily intake (TDI) of microcystins suggested by the WHO (0.04 μg/kg body weight/d). It is suggested that Nile tilapia fed on toxic cyanobacteria is not suitable for human food.     

Low-temperature tolerance of Nile tilapia, Oreochromis niloticus: effects of environmental and dietary factors

This study was conducted (1) to evaluate the effects of photoperiod (fixed vs. decreasing light), fish size (136 vs. 220 mm), dissolved ions (hardness and salinity) and diet (menhaden oil vs. coconut oil‐based) on the tolerance (survival) of Nile tilapia, Oreochromis niloticus, to low temperatures (decreased by approximately 0.5 °C per day) and (2) to evaluate the effect of dietary fatty acid composition on selected physiological characteristics of Nile tilapia exposed to decreasing temperatures. Size significantly affected mortality, with smaller fish being less tolerant to low temperatures than larger fish. Results were equivocal in the photoperiod, dissolved ion and dietary lipid experiments, and were dependent on the method of data analysis employed. Diet significantly affected plasma osmolarity, with higher values in fish fed the menhaden‐based diet. Haematocrit, serum glucose, sodium and cortisol concentrations, serum and splenic lysozyme activities, lymphocyte count and hepatosomatic index were not affected by diet. Haematocrit, white cell count and serum glucose and sodium concentrations were significantly affected by temperature, but serum and splenic lysozyme content, hepatosomatic index, and serum cortisol concentrations were not. The results of this series of experiments indicate that altering the environment or diet has little effect on the ability of Nile tilapia to survive low temperatures.     

高温诱导对尼罗罗非鱼性别分化及生长的影响

采用自雌鱼口腔中取出受精卵人工孵化的方法建立了尼罗罗非鱼家系20个。受精后9d,将各家系鱼苗分成两份,分别在28℃(对照组)和36℃(高温诱导组)下养殖,诱导处理12d后,统计高温诱导期成活率并将实验鱼转入自然水温下培育,养殖60～120d后对各实验组的雄性率及生长情况进行测定。结果表明,高温处理对仔鱼的成活率没有影响,但能显著提高某些家系的雄性率,如F27(诱导组88%,对照组49%)、F37(诱导组90%,对照组53%)和F41(诱导组91%,对照组53%);高温处理后多数家系的雄性率略有升高,但不显著;有两个家系高温诱导组雄性率低于对照组,分别是F8(诱导组43%,对照组46%)和F35(诱导组29%,对照组38%),这显示了尼罗罗非鱼性别分化受遗传和环境因子共同作用。生长情况测定结果表明,高温诱导对发育初期罗非鱼的生长没有显著影响。本研究结果说明,高温处理能显著提高某些家系的雄性率,高温诱导和家系选择有望成为高雄性率尼罗罗非鱼新品种培育的新的技术手段。     

Effect of dietary betaine levels on growth performance and hepatic intermediary metabolism of GIFT strain of Nile tilapia Oreochromis niloticus reared in freshwater

An 8‐week feeding experiment was conducted to determine the effect of dietary betaine levels on the growth performance and hepatic intermediary metabolism of genetically improved farmed tilapia (GIFT) strain of Nile tilapia Oreochromis niloticus (mean initial body weight: 78.3 ± 1.3 g, means ± SD). Six practical diets were formulated with the incorporation of betaine at the levels of 0 (control), 5, 10, 15, 20 and 25 g kg⁻¹. Survival showed no significant differences among the treatments (P > 0.05). The highest and lowest weight gain (WG) and specific growth rate (SGR) were observed for fish fed the diets containing 5 and 0 g kg⁻¹ (control) betaine, respectively. Feed intake showed similar trend with WG and SGR. In contrast, feed conversion ratio was the lowest when dietary betaine level was 5 g kg⁻¹. In general, dietary betaine supplementation showed no significant effect on hepatic composition of tilapia. Condition factor and viscerosomatic index tended to increase with increasing dietary betaine levels from 0 to 5 g kg⁻¹ and then decline when dietary betaine levels further increased from 5 to 25 g kg⁻¹. In contrast, hepatosomatic index declined with increasing dietary betaine levels (P < 0.05). Dietary betaine levels significantly influenced several hepatic enzymatic activities, including succinate dehydrogenase, lactate dehydrogenase, malic dehydrogenase, lipoprotein lipase and hepatic lipase, suggesting that dietary betaine addition had significant effects on nutrient metabolism in the liver. Based on the second‐order polynomial regression analysis of WG, 12.5 g kg⁻¹ of dietary betaine level seemed optimal for genetically improved farmed tilapia strain of O. niloticus.     

Effects of dietary protein on growth and body composition of Nile tilapia, Oreochromis niloticus L.

The effects of dietary protein (25%, 30%, 35%, 40% and 45%) on growth, survival, feed conversion ratio (FCR), protein efficiency ratio (PER) and body composition were investigated for four sizes (0.51, 45, 96 and 264 g) of Nile tilapia, Oreochromis niloticus L. In all four experiments, there was a progressive increase in growth with increasing dietary protein. In fry (0.51 g), significantly higher growth, survival and feed conversion were recorded for fish fed 40–45% rather than 25–35% protein diets. Similar trends for growth and FCR were also noted in 45 g fish. For larger (96 and 264 g) tilapia, significant differences in growth and FCR were found only between fish fed 25% and 30–45% protein diets. FCR and PER decreased with increasing weight of fish, and both were found to be negatively correlated with dietary protein level. Whole-body composition of the smallest fish was significantly influenced by dietary protein content. Percentage body protein of the fish fed 40–45% protein was higher than that of fish fed 25–35% protein diets, whereas lipid content decreased with increasing dietary protein level. In 45 g fish, both protein and lipid contents were higher in fish fed 25% and 30% protein diets than in those fed 35–45% protein diets. In larger tilapia, no significant influence of dietary protein level on body protein content was found. Percentage lipid decreased with increasing dietary protein level, and no definite trends in ash content were found. The results of these studies indicate that O. niloticus fry (0.51 g) should be reared on a practical diet containing 40% protein, and larger tilapia (96–264 g) on a diet containing 30% protein.     

饲料中海洋红酵母对尼罗罗非鱼幼鱼生长性能、消化酶及免疫酶活性的影响

为了研究海洋红酵母(Rhodotorula mucilaginosa)对尼罗罗非鱼(Oreochromis niloticus)幼鱼生长性能、消化酶及免疫酶活性的影响,配制6组饲料,分别为对照组、添加1 gkg-1、2 gkg-1、3 gkg-1、4 gkg-1和5 gkg-1的海洋红酵母组,投喂初始均质量为(5.220.01) g的尼罗罗非鱼,实验56 d。结果显示,与对照组相比,2 gkg-1和4 gkg-1组的饲料系数显著降低(P0.05),1 gkg-1、3 gkg -1和5 gkg-1组则没有显著性差异(P0.05)。5 gkg-1组鱼体粗蛋白含量显著低于1 gkg-1和2 gkg-1组(P0.05),1 gkg-1、3 gkg-1和5 gkg-1组鱼体粗灰分含量显著低于对照组(P0.05)。与对照组相比,1 gkg-1组胃蛋白酶活性显著升高(P0.05),3 gkg-1、4 gkg-1和5 gkg-1组胃蛋白酶活性显著降低(P0.05)。2 gkg-1和3 gkg-1组前肠和中肠淀粉酶和脂肪酶,以及肝脏溶菌酶和一氧化氮合酶活性均显著高于对照组(P0.05)。根据尼罗罗非鱼幼鱼的消化酶和免疫酶活性等指标综合分析得出,海洋红酵母在罗非鱼饲料中的建议添加量为2～3 gkg-1。     

木薯粉对罗非鱼生长、饲料利用和鱼体营养成分的影响

选择健康的吉富罗非鱼(体重1.29±0.25 g)为实验鱼,配制五种木薯粉含量分别为0%、10%、20%、30%和40%的等氮(粗蛋白为32%)、等能(总能为16 kJ·g-1)实验饲料,饲喂罗非鱼56 d,每饲料组设三个重复,研究不同含量木薯粉对吉富罗非鱼生长、饲料利用及全鱼营养成分的影响.结果表明:(1)木薯粉能提高罗非鱼的增重和蛋白质效率,其中以40%木薯粉组的效果最佳,其增重率、蛋白质效率和饲料系数分别为1470.99%(P＜0.05)、2.36(P＜0.05)和1.27(P＜0.05).(2)40%木薯粉组的干物质和蛋白质的表观消化率分别较对照组提高13.87%(P＜0.05)和7.93%(P＜0.05).(3)40%木薯粉组的全鱼粗蛋白、粗灰分分别较对照组显著提高7.07%(P＜0.05)和8.78%(P＜0.05),粗脂肪降低了13.00%(P＜0.05).     

Effect of environmental calcium levels on calcium uptake in tilapia larvae Oreochromis mossambicus

Effects of environmental calcium concentrations on the survival, growth, body calcium content and calcium uptake kinetics in developing tilapia (Oreochromis mossambicus) larvae were studied. Fertilized eggs were incubated in high- and low-calcium artificial freshwater (0.88–0.96 mmol l^–1 vs. 0.02–0.03 mmol l^–1 CaCl₂ or CaSO₄) until 3 days after hatching. Tilapia larvae showed similar hatching rates and wet weights in either high- or low-calcium medium, indicating neither the development nor the growth in tilapia larvae was affected by the environmental calcium levels. The body calcium content in low-calcium groups was about 90–95% that of high-calcium groups, No matter what calcium source was used (CaCl₂ or CaSO₄), acclimation to low calcium medium caused a stimulation of calcium uptake (measured in 0.2 mmol l^–1 calcium),i.e., 1.2–1.3 fold higher than that of high calcium groups. This enhanced calcium uptake capacity was characterized by a 50% decrease in K_m and a 25% increase in J_max. Effect of different calcium salts on calcium influx was significant only in low calcium level,i.e., calcium influx in low-CaCl₂ group higher than that in low-CaSO₄ group. These results suggest that tilapia larvae are able to modulate their calcium uptake mechanism to maintain normal body calcium content and growth in environments with different levels of calcium.     

Response of Nile tilapia (Oreochromis niloticus) to diet acidification: Effect on growth performance and feed utilization

A 12-week feeding trial was undertaken to assess growth, nutrient utilization, some hematological parameters, and proximate composition of Nile tilapia (Oreochromis niloticus) fed diets supplemented with graded levels (0.5%, 1.0%, and 1.5%) of two blends of organic acids or organic salts. Seven isonitrogenous (300 g CP kg^?1) and isocaloric (19.0 MJ gross energy kg^?1) diets were formulated. The control diet (D1) contained neither added blend of organic acids nor organic salts. Three diets (D2, D3, and D4) were supplemented with 0.5%, 1.0%, and 1.5% of malic acid + oxalic acid blend (OAB), respectively. The other three diets (D5, D6, and D7) were supplemented with 0.5%, 1.5%, and 1.5% of calcium lactate + sodium acetate blend (OSB), respectively. Fingerlings (7.05 ± 0.02 g) were randomly distributed into 21 glass aquaria (160 liter), with each aquarium holding 15 fish. At the end of the feeding trial, O. niloticus offered the control diet showed lower growth and feed utilization than all those fed the organic acids or organic salts blends supplemented diets. Fish fed the diet D3 showed the highest body weight (BW), body length (BL), weight gain (WG), specific growth rate (SGR), feed intake (FI), and the best feed conversion ratio (FCR) and protein efficiency ratio (PER). Fish fed diet supplemented by 1.5% OAB (D4) showed the highest serum protein content, while control group (D1) showed the lower level of total lipids compared with the other treatments. Fish group fed the diet supplemented with 0.5% of OSB (D5) showed the highest protein and ash contents and the lowest lipid content of the whole fish body, while the control group showed the lowest protein and the highest fat content. The present observations suggest that the growth, feed utilization, and health status of juvenile O. niloticus can be enhanced with a supplementation of 1% of OAB or OSB in the diet.     

Effect of dietary protein-energy levels and fish initial sizes on growth rate, development and production of Nile tilapia, Oreochromis niloticus L.

The effects of dietary protein‐energy levels on the growth rate, proximate composition and production were examined in Nile tilapia, Oreochromis niloticus, at two starting weights (22.9 and 39.8 g) reared in concrete ponds for 180 days. The highest weight gain (183.1 g) was obtained with fish fed a 30% protein and 10.5 kJ g^?1 diet for the small initial size and 180.2 g for a diet containing 25% protein and 12.6 kJ g^?1 for the large initial size. Dressed yields (edible mass) and fillets increased to 56.9% and 52.5% in fish fed diet with 25% protein and 10.5 kJ g^?1 at the initial size of 22.9 g, while fish started at 39.8 g exhibited the best values (56.5% and 52.1%) when fed the 30% protein and 10.5 kJ g^?1 diet. Proximate composition of soft tissue (wet weight basis) in small fish was significantly influenced by dietary protein‐energy levels. Protein was 26.1±0.3% in fish fed the high protein (30%) and low energy (10.5 kJ g^?1 diet), while lipid content was 6.4±0.3% at diet containing 20% protein and 14.7 kJ g^?1 diet. Large initial size fish fed the diet with 25% protein and 14.7 kJ g^?1 had the highest body protein (32.0±0.4%) and lowest lipid content (2.2±0.3%). Feed conversion ratio (FCR) and protein efficiency ratio varied with different dietary protein‐energy levels and initial fish sizes. Feed conversion ratio increased with increasing protein and decreasing energy level in the diet, and values in small fish were higher than values in large fish. Protein efficiency ratio decreased with increasing dietary protein level and decreasing energy level. The maximum total production (7.6 tons feddan^?1) was with dietary high protein (30%) and low energy (10.5 kJ g^?1) for small‐sized fish, while large initial fish had the highest production (3.7 tons feddan^?1) when fed the 25% protein and 12.6 kJ g^?1 diet energy. Starting with 22.9 g fish was more advantageous than the initial size of 39.8 g for rearing Nile tilapia. Small fish required a high‐protein and low‐energy diet, whereas large fish required a low‐protein and high‐energy diet to achieve highest production.     

Effect of dietary l‐methionine concentrations on growth performance,serum immune and antioxidative responses of juvenile Nile tilapia,Oreochromis niloticus

An 8‐week feeding trial was conducted to determine the effect of dietary l ‐methionine supplementation on growth performance, serum immune and antioxidative responses of juvenile Nile tilapia Oreochromis niloticus. Six iso‐nitrogenous (282 g kg^?1 crude protein) diets were formulated to contain graded levels of methionine (0.32%, 0.54%, 0.75%, 0.93%, 1.14% and 1.33% of dry weight) at a constant dietary cysteine level of 0.83 g kg^?1. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (2.3 ± 0.0 g), which were fed three times daily (8:30, 12:30 and 17:00 hours). The results showed that growth performance and feed utilization significantly improved when dietary methionine levels increased (P < 0.05). Using quadratic regression analysis of weight gain against dietary methionine levels indicated that, the optimal dietary methionine requirement for maximum growth of juvenile tilapia was 9.12 g kg^?1 of the dry diet in the presence of 0.83 g kg^?1 cystine. In addition, maximum C4 content and lysozyme activity were observed in fish fed 7.50 g kg^?1 methionine diet; maximum C3 content and superoxide dismutase activity were obtained in fish fed 9.30 g kg^?1 dietary methionine level. While there was no significant difference in serum glutathione peroxidase activity among all methionine supplemented treatments (P > 0.05). Methionine supplementation decreased malondialdehyde content in serum significantly (P < 0.05) when compared with the control diet, while there was no significant difference among supplemented treatments. These data suggested that l ‐methionine affected antioxidant status and promoted serum immune response in juvenile Nile tilapia, and at non‐stressed status, the requirement of dietary methionine in maintaining normal immunity and physiology is lower than that for maximum growth.     

Effect of gelatinization degree and inclusion level of dietary starch on the characteristics of digesta and faeces in Nile tilapia (Oreochromis niloticus (L.))

Higher faeces removal efficiency can help and reduce the negative impact of faecal waste on water quality and on the environment. Physicochemical properties of feed ingredients/nutrients may change the faeces characteristics and the ratio of removed to non-removed solids. The aim of this study was to assess what physicochemical properties of the diet (viscosity, fermentation and dry matter) influence faeces characteristics and faeces removal using Oreochromis niloticus (L.) as the test animal. Four experimental diets were formulated by the addition of two types of starch differing in gelatinization degree (gelatinized and native) and two levels (high and low) of starch to a basal diet according to a 2 × 2 factorial design. The diets were assigned to 16 tanks with 40 fish each, with four replicates for each diet. Replacement of native starch by gelatinized starch improved faeces removal rate, growth and digestibility (P < 0.01), but reduced fermentation (P < 0.05) at the end of the intestine. Addition of gelatinized starch did not change viscosity and dry matter of the digesta at the end of the intestine. A high level of starch in the diet also increased digestibility, growth and faeces removal percentage (P < 0.05). Fermentation and dry matter content at the end of the intestine were not influenced by a high starch diet, but viscosity was higher at the high level of starch inclusion. Volatile fatty acid levels in the stomach of Nile tilapia were high in the treatments with gelatinized starch. In conclusion, intestinal fermentation induced by native starch had a negative impact on faeces removal efficiency. A higher inclusion level of starch resulted in a higher viscosity of the digesta, leading to higher faeces removal efficiency.     

饲料磷水平对吉富罗非鱼肠道磷和脂肪酸转运及甘油三酯沉积的影响

摘要:为了探究饲料中不同磷水平对罗非鱼肠道磷和脂肪酸转运及甘油三脂沉积的影响,我们配制了3组不同磷水平的饲料,饲料中磷含量分别为1.21 %（LPD）、1.75 %（MPD）和2.66 %（HPD））,用配制的饲料投喂罗非鱼10周。结果显示：与LPD组相比,HPD组显著增加罗非鱼肠道钠磷协同转运体SLC34A2基因（95.7%）和蛋白（200.1%）的表达,增加肠道组织总磷含量（79.2%）;HPD组上调脂肪酸吸收基因cd36、fabp1、fabp2和fatp1及甘油三酯合成基因dgat1的表达（11.2%~54.0%）,下调脂肪酸转运基因apob-100的表达（37.7%）,增加游离脂肪酸（NEFA）的含量（241.1%）。与LPD组相比,HPD组显著增加罗非鱼肠道组织甘油三酯（TG）的含量（42.9%）。 综上,我们的研究表明,饲料中高磷水平增加肠道组织TG的含量,上调脂肪酸吸收途径和抑制脂肪酸排出途径。我们的研究为深入揭示磷影响鱼类磷代谢及脂类代谢的机理奠定基础。