Growth, Survival, and Biochemical Composition of Freshwater Prawns Macrobrachium rosenbergii Fed Natural Food Organisms Under Controlled Conditions

Under production conditions freshwater prawns Macrobrachium rosenbergii are supplied nutrients by a combination of prepared diets and natural pond organisms. For maximum production efficiency and profitability it is important that the nutritional contributions of natural foods be identified and quantified. In this study the relative importance of forage organisms previously identified as important natural foods for prawns in ponds were evaluated under controlled conditions. Juvenile prawns (average weight 1.80 ± 0.06 g) were stocked into 18 37.5-L aquaria at a density of 10 prawns per tank. The six dietary treatments tested were: 1) unfed (negative control); 2) commercially prepared diet (positive control); 3) oligo-chaetes; 4) chironomids; 5) zooplankton; and 6) a combination of the latter three. Each treatment was evaluated in triplicate aquaria for 7 wk. The growth rate of prawns in the unfed treatment was statistically lower than in fed treatments ( P < 0.05). There were no significant differences ( P > 0.05) between growth rates and survivals among prawns in the five fed treatments. Selective retention of arachidonic acid (20:4n-6), eicosapentanoic acid (22: 5n-3), and docosahexanenoic acid (22:6n-3) in unfed prawns likely indicates the relative nutritional importance of these fatty acids. Comparisons of whole-body fatty acid and amino acid concentrations of prawns and food organisms indicate that zooplankton and oligochaetes may have the most appropriate biochemical compositions as prawn food sources.     

Effect of Stocking Density on Growth and Water Quality for Largemouth Bass Micropterus salmoides Growout in Ponds

Juvenile largemouth bass Micropterus salmoides , trained to accept artificial diets, were stocked into six 0.04-ha ponds at stocking densities of either 6,175 or 12,350 fish/ha. Fish were fed a floating custom-formulated diet, containing 44% protein, once daily to satiation for 12 mo (May 1994–May 1995). At final harvest, the total yield of fish was significantly greater (P < 0.05) and feed conversion ratio (FCR) was significantly lower, for bass stocked at the higher density (4,598 kg/ha and 2.3, respectively) than when stocked at the lower density (2,354 kg/ha and 3.3, respectively). There was no significant difference (P > 0.05) in average weight, length, or survival of bass stocked at the two densities. Averaged over the study period, there were no significant differences (P > 0.05) in total ammonia-nitrogen (TAN), nitrite-nitrogen, or un-ionized ammonia concentrations in ponds in which bass were stocked at the two densities. These data indicate that largemouth bass of the size used in this study are amenable to pond culture at densities of at least 12,350 fish/ha and that higher stocking densities may be possible.     

Effects of Added Substrate on the Production and Population Characteristics of Freshwater Prawns Macrobrachium rosenbergii in Ponds

The effects of added substrate on the growth and population characteristics of freshwater prawns raised in ponds were evaluated. Juvenile prawns (0.3 × 0.2 g) were stocked into six 0.04-ha ponds at a density of 59,280/ha. In three randomly selected ponds artificial substrate was added sufficient to increase available surface area approximately 20%. Three control ponds received no added substrate. Added substrate consisted of PVC frames with horizontal plastic mesh and vertical suspended seines. Prawns were fed a commercial diet (32% protein) twice daily according to a computer-generated feeding schedule. At harvest average individual weight, daily yield, and total yield were significantly higher (P < 0.05) in ponds with added substrate (37 g, 12.0 kg/ha per day, and 1,268 kg/ha, respectively). There was no significant difference in survival between treatments, averaging 59% overall. In ponds without substrate the number of small males (SM) was significantly higher and the number of orange claw males (OC) was significantly lower than in ponds with added substrate. Average individual weights of blue claw males, orange claw males, reproductive females, and virgin females were significantly higher (P × 0.05) in ponds with added substrate. Prawns raised in ponds containing added substrate had growth rates and population structures characteristic of prawns stocked at lower densities. Optimum relationships between stocking rates and amounts and types of added substrate should be evaluated as possible methods to increase production levels.     

Characterization of dietary protein in Brassica carinata meal when used as a protein supplement for beef cattle consuming a forage-based diet

As a novel oilseed crop in Florida, Brassica carinata has the capacity of producing high-quality jet biofuel, with a protein-dense meal (~40% crude protein; CP) obtained as a by-product of oil extraction. Characterization of the meal protein is limited, yet necessary for formulation of beef cattle diets; therefore, the objective of this experiment was to determine ruminal and postruminal digestibility of protein from B. carinata. Eight ruminally cannulated Angus crossbred steers (473 ± 119 kg) were used in a duplicated 4 × 4 Latin square design, in which in situ ruminal and postruminal degradability of nutrients were evaluated. The three-step in vitro procedure was used to compare CP and amino acid (AA) degradation in B. carinata meal pellets (BCM) with that of cottonseed meal (CSM), dry distillers grains with solubles (DDGS), and soybean meal (SBM). In situ bags were incubated in the rumen for 0 to 96 hr, with the undegraded supplement remaining after 16 hr subjected to serial in vitro enzymatic solutions. Data were analyzed using the MIXED procedure of SAS. Ruminal rate of degradation of dry matter, organic matter, and CP was greatest (P ˂ 0.01; 10.9, 11.3, and 11.5 %/h, respectively) for SBM. Rumen degradable protein (RDP) content did not differ (P = 0.20; 47.8% and 55.1%, respectively) between CSM and DDGS, but was decreased (P ˂ 0.01) compared with SBM and BCM, which did not differ (P = 0.99; 72.3% and 71.8% RDP, respectively). Compared with DDGS, SBM had greater (P < 0.01) intestinal digestibility of rumen undegradable protein (RUP). Intestinally absorbable digestible protein (IADP) was greatest (P < 0.01) for CSM, with SBM and BCM having the least IADP. Total tract digestibility of CP (TTDP) was greater (P < 0.01) for SBM compared with CSM and DDGS. The contribution of RUP to intestinally absorbable AA was 7.2 and 3.1 g of lysine and methionine per kilogram of CP in BCM, respectively. The evaluation of B. carinata meal as protein supplemented for cattle consuming a forage-based diet resulted in 71.8% RDP and 97.1% TTDP, thus indicating its viability as a high-quality protein supplement for beef cattle.