Kevin C. Williams

The fate of nitrogenous waste from shrimp feeding

This study characterized and quantified the dissolved nitrogen (N) waste from shrimp (Penaeus monodon) feeding. The subsequent utilization of the dissolved N (DN) compounds by the microbial community in shrimp pond water was also examined. There were three main sources of soluble N from feeding; gill excretion, leaching from formulated feed, and leaching from shrimp faeces. The main source of DN was ammonia excreted from shrimp gills. However, there was also a significant amount of DN leached from feed and faeces over the course of a few hours. Most of this was in the form of dissolved organic N (DON) compounds. In the case of feed, a significant proportion of this was dissolved primary amines (DPA, 23%) whilst in faeces, it was urea (26%). Urea leached from shrimp faeces was rapidly utilized by the microbial community in pond water. However, other DON compounds appeared to be less bioavailable. Dissolved organic N leached from formulated feed appeared to be less effectively utilized by the microbial community and is likely to accumulate in pond water. Dissolved organic N leachates from formulated feed and faeces are, therefore, likely to have a significant impact on water quality in shrimp ponds, both by the accumulation of DON, and stimulation of the growth of the microbial community. There is, therefore, considerable scope to improve water quality, and hence reduce nutrient discharges from shrimp farming, by reducing overfeeding, and improving feed retention by shrimp.

Asian seabass Lates calcarifer perform well when fed pelleted diets high in protein and lipid

Under controlled (28 °C and 12:12 photoperiod) freshwater recirculation conditions, two 48-tank (180 l) experiments tested the hypothesis that the dietary crude protein (CP) specification for Asian seabass could be reduced by increasing the dietary concentration of lipid. In Experiment 1, 384 fish (230 g initial bodyweight) were fed air-dry extruded diets of 38%, 42.5%, 47.3% and 52% CP in combination with lipid concentrations of 7.0%, 12.8% and 18.3% (12 diets) for 8 weeks. In Experiment 2, 720 juvenile fish (80 g initial bodyweight) were fed for 6 weeks one of 12 air-dry diets that varied in lipid between 11.5% and 22.4% and in protein between 43.8% and 64.7%. Air-dry feed conversion ratio (FCR) and growth rate improved linearly with increasing dietary CP and improved step-wise with increasing dietary lipid from 1.48 to 0.86 g/g and 2.69 to 4.86 g/day, respectively, in Experiment 1 and similarly from 1.00 to 0.78 g/g and 2.27 to 3.10 g/day, respectively, in Experiment 2. In terms of growth rate and FCR, a small protein sparing effect of lipid was observed which was more pronounced for the smaller fish (Experiment 2). Increasing dietary CP resulted in very little change in the proportion of dietary N that was retained by the fish (35% to 42% in Experiment 1 and 25% to 31% in Experiment 2). In both experiments, retention of dietary gross energy improved as dietary lipid increased, with fat deposition appearing to be a major component of this energy conservation (total DM body lipid content increasing from 24.0% to 29.1% in Experiment 1 and from 20.3% to 32.7% in Experiment 2). However, DM lean gain increased linearly with increasing dietary CP over the range examined and was not influenced by the amount of lipid in the diet, indicating that any protein sparing by lipid was due to increased body fat deposition. The results show that productivity of Asian seabass can be markedly improved by increasing dietary protein and lipid concentrations. However, Asian seabass appear to have only a limited capacity to use lipid as a primary energy source. In this aspect, they differ markedly from salmonids.

The dietary protein and lipid requirements of post-puerulus western rock lobster, Panulirus cygnus

Abstract The dietary requirements of post-puerulus western rock lobster for protein and lipid (fat) were examined in a 6-week, pair-fed feeding study. Incremented dietary amounts of protein (30%, 35%, 40%, 45%, 50% and 55%) at each of two dietary fat levels (6% and 10%) were examined. An additional diet of fresh mussels ( Mytilus edulis ) was included as a reference. At the end of the 6-week growth experiment, growth of the rock lobsters was better when protein levels were greater than 50% of the diet. Growth of rock lobsters was also significantly greater in diets with the lower fat levels. The growth of the animals fed the reference diet was significantly superior to all of the experimental diets. Survival of animals in all treatments was equal to or greater than 75%. Though there were some significant differences in survival among treatments, this was not consistent with any relationship between either protein or fat content of the diets. The number of moulting events observed in each of the test treatments was significantly lower than that observed by the mussel-fed animals. This was consistent with what was observed with the level of growth difference among the test treatments and the mussel-fed treatment. There were no significant differences in the number of moulting events among any of the protein-lipid level treatments. There were no significant differences among the test treatments with feed intake on a proportion of body weight basis. This was in accordance with the pair-feeding protocol of this study. Feed conversion by the lobsters in each of the test treatments was in accordance with what was observed in their corresponding growth responses. Diets containing 6% fat and either 50% or 55% protein had significantly lower FCR values than all other test diets (2.7:1 and 2.5:1, respectively). The diet that had 10% fat and 30% protein had the highest FCR (7.6:1) and was significantly higher than all other diets. There were no other significant differences in feed conversion among the test treatments. The results of this study support that post-puerulus Panulirus cygnus have a very high dietary protein requirement and a poor capacity to utilise dietary lipid. It should be noted though that the relative growth of the post-puerulus P. cygnus fed the pelleted diets was considerably lower than of those fed the reference diet of fresh mussels. Accordingly, optimal diets derived from this study should be based on fat levels of about 6% and protein levels equal to or exceeding 55%.

Apparent digestibility of selected feed ingredients for humpback grouper, Cromileptes altivelis

Abstract The dry matter (DM), crude protein (CP) and gross energy (GE) apparent digestibility of nine feed ingredients locally available in South Sulawesi were determined with juvenile (∼20 g) humpback grouper. In each of the three 4×4 latin square experiments, humpback grouper were fed a reference diet and three other diets in which test feed ingredients were substituted at rates of either 40% or 30% for animal or plant sources, respectively. Chromic oxide was used as the indigestible marker. Faeces were collected by sedimentation at 3-h intervals. Each experiment entailed four collection periods with each diet being randomly changed between the tanks. The apparent digestibility of GE could not be determined for three feed ingredients as the amount of collected faeces was insufficient for energy analysis. The derived DM, CP and GE apparent digestibility coefficients (ADC; means±S.D.) for the test feed ingredients were, respectively: shrimp head meal—58.5±3.33, 78.0±1.32 and 63.6±0.89; soybean meal—54.8±2.72, 67.2±1.29 and 51.1±0.89; palm oil cake meal—45.3±2.37, 80.5±1.30 and 40.4±3.74; oven-dried blood meal—48.1±0.85, 55.2±1.35 and not determined (nd); formic acid-fermented blood meal—67.9±1.63, 87.5±0.55 and nd; propionic acid-fermented blood meal—61.7±2.60, 84.2±0.69 and nd; local sardine meal—87.2±2.53, 92.5±1.40 and 85.2±0.90; local fish meal—59.1±1.23, 82.4±1.99 and 77.2±1.91; and rice bran meal—22.2±1.52; 59.5±1.41 and 44.3±0.97. The protein of both plant and animal feed ingredients was well digested by humpback grouper, while the DM and GE of the protein-rich animal feed ingredients were more digestible than the carbohydrate-rich plant feed ingredients.

Optimising the essential fatty acids in the diet for weight gain of the prawn, Penaeus monodon

Abstract A study of the influence of the proportion of dietary essential fatty acids (EFA) in the lipid of diets fed to the prawn, Penaeus monodon , showed clearly that these nutrients are required as a proportion of the total fatty acids in the diet. A factorial array of diets were prepared to contain optimal levels (g kg −1 ) of the fatty acids, linoleic (LOA, 18:2 n −6), linolenic (LNA, 18:3 n −3), eicosapentaenoic (EPA, 20:5 n −2) and docosahexaenoic (DHA, 22:6 n −3). As a second factor to the study, the total amount of lipid in the diet was also increased at incremented levels from 45 to 135 g kg −1 at 30 g kg −1 increments. The weight gain of prawns was greatest (156.2±6.2%) when their diet contained 75 g lipid kg −1 , of which 30 g kg −1 was essential fatty acids. Weight gain of prawns fed with diets containing 45 g lipid kg −1 with 17 g of essential fatty acids kg −1 was greater (148.0±3.4%) than prawns fed with the diet that had 45 g lipid kg −1 and 30 g of essential fatty acids kg −1 (124.0±6.8%). The nutritional condition of the prawns, as determined by the amount of lipid in their digestive glands, was generally reflective of weight gain, though there were exceptions, with higher lipid levels in prawn DG from faster growing prawns. The fatty acid composition of the DG lipid generally mimicked that of the dietary lipid. The proportions of each of the essential fatty acids in the DG lipid varied marginally between treatments, but generally LOA, LNA, EPA and DHA levels in the DG fatty acids were present in slightly lower proportions than that in the diet. The amount of dietary lipid present influenced the composition of the fatty acids in the DG lipid when the lowest inclusion level of lipid was compared with the higher inclusion levels. The results of this study clearly indicate that EFA are required as a proportion of the total fatty acids in the diet, and not as a proportion of the diet. Accordingly, it is suggested that EFA should be defined as a percentage of the total fatty acids in conjunction with an indication of the amount of lipid in the diet. This study also showed that for weight gain, the optimal total lipid level of the diet is less than 105 g kg −1 .

The effects of dietary lipid amount and fatty-acid composition on the digestibility of lipids by the prawn, Penaeus monodon

The digestibilities of the lipid content, and the fatty acids of this lipid, were examined in each of a series of the diets designed to examine the optimal fatty-acid and lipid requirements for the giant tiger prawn, Penaeus monodon. Digestibility of the total lipids was similar for dietary lipid levels of 45, 75 and 105 g kg−1 though the digestibility of total lipids in diets with lipid levels of 135 g kg−1 was significantly (P<0.05) lower. Digestibility of total lipids was unaffected by fatty-acid composition, except when the level of dietary polyunsaturated fatty acids was 17 g kg−1 of the diet and total lipid content was greater than 45 g kg−1. Highest fatty-acid digestibilities were observed for the long-chain highly unsaturated fatty acids, eicosapentaenoic (20:5n−3) and docosahexaenoic (22:6n−3) acids. High levels of digestibility were observed for all fatty acids with unsaturated bonds including the monounsaturated fatty acid, oleic acid (18:1n−9). Longer-chain saturated fatty acids were the least digestible, with digestibilities diminishing as fatty-acid chain length increased. The results of this study clearly demonstrate that amount of lipid in the diet influences its own digestibility and also that the fatty-acid composition of the total lipid in the diet influences the digestibility of the total lipid and also that of the individual fatty acids.