ALBERT

Notes: A fish feeding trial was conducted in a warm-water recirculating system for 8 weeks to assess the nutritive value of processed mucuna seeds as a dietary protein replacement for fish meal in practical diets of tilapia. Diets 2–6 contained mucuna seeds processed as follows: raw, soaked in water, soaked in sodium bicarbonate solution (0.07%), soaked in ascorbic acid solution (0.1%) or soaked in water containing 3% of freeze-dried moringa leaf powder, followed by autoclaving. The mucuna seed meals were then used to replace 25% of the total dietary protein in each diet. The performance of fish fed these diets was compared with fish fed a fish meal-based control diet (diet 1), which contained 35% protein. All diets were prepared to be isonitrogenous and isoenergetic. Each treatment had three replicates, using seven fish per aquarium, with a mean initial body weight of 3.9 ± 0.06 g. Fish were fed five times about their maintenance level (3.0 g feed × body weight (kg)−0.8 day−1), and no mortality was observed during the experiment. The growth rate, feed conversion ratio and protein productive value of fish fed diets 1, 3, 4, 5 and 6 were similar. However, with regard to energy retention and apparent net lipid utilization, the values observed in fish fed diet 1 were similar to those of fish fed diets 5 and 6, and diet 6, and significantly higher than other dietary groups. Fish fed diet 2 showed a significantly (P 〈 0.05) reduced growth performance, higher carcass moisture and ash contents, and lower levels of lipid and energy compared with all other dietary groups. Fish fed diet 2 had a significantly lower plasma cholesterol level compared with other diets. However, no significant variation of muscle cholesterol was found between the dietary groups. Even though the hepato-somatic index of the fish fed diets 3, 4, 5 and 6 was significantly lower than diet 1, these values appeared to be significantly higher compared with fish fed diet 2. The present study indicates that the inclusion of mucuna seed meal (replacement of 25% of total dietary protein of feed) after soaking in any one of the tested solutions followed by autoclaving significantly improved the growth performance and feed utilization of tilapia compared with that of the raw seeds. Moreover, these values were similar to the performance obtained with the fish meal-based control diet 1. This might be due to the relative reduction of anti-nutrients, particularly the non-protein amino acid 3, 4-dihydroxyphenylalanine, and increased palatability and nutrient availability of processed beans.

Notes: 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.

Notes: An 8-week feeding trial was conducted in a warmwater recirculation system at 27 ± 0.2 °C to evaluate the nutritive value of dhaincha (Sesbania aculeata) seed meal as a possible fish meal substitute in the diet of tilapia. Five isonitrogenous and isoenergetic diets were formulated to contain 32% crude protein and 18.4 kJ g−1 gross energy. Sesbania seed meal was included in diets at various levels [0%, 9.7%, 19.4%, 29.1% and 38.8% for diets 1 (control), 2, 3, 4 and 5, respectively, which correspond to 0%, 10%, 20%, 30% and 40% of dietary crude protein]. Each treatment had two replicates, eight fish per replicate, with mean initial weight of 7.06 ± 0.03 g. Fish were fed 20 g kg−1 metabolic body weight daily. On the basis of the observed growth rate, feed conversion ratio, protein efficiency ratio, apparent net protein utilization and energy retention, diets 1 (control) and 2 (containing 9.7% Sesbania meal) were similar and significantly (P 〈 0.05) better than the other dietary groups. Fish fed diets 3, 4 and 5 containing higher levels of Sesbania meal showed significantly reduced growth performance compared with those fed diets 1 and 2. Fish fed diets 3, 4 and 5 had significantly lower faecal dry matter (DM) content, apparent crude protein, lipid and energy digestibility and reduced levels of cholesterol compared with the control and diet 2. Fish fed diets containing higher levels (〉9.7%) of Sesbania meal had significantly higher whole-body moisture, lower lipid and gross energy content. The lower growth performance of fish fed diets containing higher levels of Sesbania meal is thought to result from the presence of tannins, saponin and the non-starch polysaccharide content of the seed. The results of this study showed that inclusion of up to 9.7% untreated Sesbania seed meal (10% of the dietary protein) in the diet did not affect the growth performance and nutrient utilization in tilapia.

Notes: The suitability of raw and methanol-extracted moringa (Moringa oleifera Lam.) leaf meal to replace 10%, 20% and 30% of the total fishmeal-based dietary protein in tilapia feeds was tested. Ten isonitrogenous and isocalorific feeds (35% crude protein and 20 MJ kg−1 gross energy), denoted as diets 1 (fishmeal-based control), 2, 3, 4 (containing 13%, 27% and 40% raw moringa leaf meal), 5, 6, 7 (containing 11%, 22% and 33% methanol-extracted moringa leaf meal), and 8, 9, 10 (containing methanol-soluble extracts of the raw moringa leaf meal at the same level as would have been present in diets 2, 3, 4) were prepared. Forty tilapia (16.7±2.4 g), kept individually, were fed the experimental diets (four fish per treatment) at the rate of 15 g feed per kg metabolic body weight (kg0.8) per day. A reduction in the growth performance was observed with an increasing level of raw moringa leaf meal (diets 2–4), whereas inclusion of methanol-extracted leaf meal (diets 5–7) had no significant (P〈0.05) effect on the growth performance compared with the control (diet 1). The growth performance of fish fed diets 8–10 containing methanol extracts of the moringa leaf meal were also similar to the control. The chemical composition values of the gained weight showed that lipid accretion decreased with increased inclusion of moringa leaves, and ash content increased. Dietary moringa methanol extracts reduced protein accretion, but had no effects on lipid and ash contents compared with the control. The inclusion of raw, methanol-extracted residues and methanol extracts of the moringa leaf meal (diets 3 and 4, 5, 6 and 7, and 8 respectively) reduced the plasma cholesterol content significantly. Similarly, a significant reduction in muscle cholesterol was observed in fish fed the diets 4, 8, 9 and 10. It was concluded that the solvent-extracted moringa leaf meal could replace about 30% of fishmeal from Nile tilapia diets.

Notes: Two studies were conducted to test the relationship between androgens and routine metabolism in the Mozambique tilapia Oreochromis mossambicus. In the first study, endogenous levels of plasma levels of androgens and oxygen consumption rate were measured. In accordance with expectations routine metabolism corrected for metabolic body mass, was positively correlated with the behaviourally active metabolite of testosterone, 11-ketotestosterone, but not with testosterone itself. In the second study levels of 11-ketotestosterone were experimentally elevated, which increased the lowest values of (corrected) routine metabolism, indicating a positive relationship with standard metabolism. These results show the importance of measuring reproductive hormones, and are supportive of the hypothesis that elevated levels of androgens are a costly trait.

Notes: The present study assessed the suitability of titanium(IV) oxide, TiO2, as a digesta passage marker in Nile tilapia Oreochromis niloticus and studied the shape of the evacuation curve in this species. In three separate trials, fish were given one dose of either 0·5, 0·25 or 0·1% of their body mass (% BME) of feed marked with 1% TiO2 or 0·5% BME of the same feed without marker. The fish were serially slaughtered at intervals after feeding and the stomach contents analysed for dry mass and marker content. The data for individual trials were analysed with the linear, square root, surface area and exponential evacuation models and parameter comparisons showed that, although the marker interfered slightly with the evacuation process, true meal size could be predicted more accurately from the marker data. The results of an analysis of the combined data sets suggested that stomach evacuation in this species is dependent more on food particle surface area (surface area model) than on stomach content mass (exponential model) as is generally assumed. On the basis of these results, it was concluded that TiO2 at an inclusion level of 1% is an acceptable marker for quantifying evacuation with a view to predicting food consumption but should be used with caution in digestibility studies.

Notes: Tilapia hybrids of Oreochromis niloticus × O. aureus with a starting weight of 90 g were grown for 57 days in 18 floating net-cages set up in a fishpond (1.8 ha × 3 m deep; water temperature around 27 °C) at the Aquaculture Research Station in Dor, Israel. They were fed pellets of a commercial diet which contained 8.1 ppm natural l-carnitine. This diet was then supplemented with 150 or 450 ppm of l-carnitine. The results show that at the end of the 8-week feeding trail, l-carnitine supplementation did not influence weight gain. The subsequent histological characteristics of the pond fish were compared with those of a separated group of their siblings kept in an indoor tank in clean flow-through water. Normal and contact epi-microscopy, contact fluorescent microscopy and contact microfluorometry with various fluorescent probes revealed that the fish fed the diet with 150 ppm of supplementary l-carnitine showed the lowest permeability to fluorescein in gills, gut and skin epithelia, the highest activity in the system of active transport for organic anions, and the highest levels of the multixenobiotic resistance transporter (MXRtr) for lipophilic/amphiphilic xenobiotics. The MXRtr activity in the liver bile canaliculi and renal proximal tubules of this group of fish was much higher than that of the other groups except those from the indoor tank. The intralysosomal accumulation of neutral red in their head kidney macrophages was also significantly higher. The results suggest that a low level of l-carnitine enrichment provides several protective effects in fish reared under intensive pond-culture conditions.