Location: Warmwater Aquaculture Research Unit
2012 Annual Report
Fifteen one-acre ponds at Delta-Western Research Center, Indianola, MS, will be filled with well water and treated with 20 mg/L KMnO4 as a prophylaxis for Proliferative Gill Disease prior to stocking fish. The ponds will be stocked with 6,000 channel catfish per acre averaging 250-500 pounds/1000 (stocker size). Eight one-acre ponds will serve as controls while seven one-acre ponds will serve as the test group (or vice versa). Fish will be supplied by Delta Western. If the stocked fish are from different source ponds, fish from each source pond will be alternately stocked in control and test ponds. Fish in control ponds will be fed a 32% crude protein commercial floating diet while fish in test ponds will be fed the same 32% crude protein commercial diet supplemented with Biomin® at 200 g/ton. Both diets will be made in 10-15 ton batches on the same day so changes in diet composition during the year resulting from least-cost formulations are similar for both treatments. On day 0, fish will be randomly stocked into 15 ponds. The mean weight of each pond will be based on a sample of 500-600 fish. The fish will be fed once per day to apparent satiation and the amount of feed consumed by fish in each pond will be recorded daily. Temperature and dissolved oxygen (DO) concentration will be measured at two-hour intervals throughout the night. Aeration (provided by one five-hp paddlewheel aerator per pond) will be initiated when the DO drops to 4 mg/L. Aerators will be turned off in the morning when the DO is 4 mg/L and rising. Aerator run times will be recorded for each pond daily. Salt (NaCl) will be added to maintain a chloride concentration of 100 mg/L as a prophylaxis against methemoglobinemia (brown blood). Sick fish will be taken to the National Warmwater Aquaculture Center (NWAC) diagnostic laboratory and only approved treatments will be applied. Where not stated, normal aquaculture practices will be used.
At the end of the six-month study, ponds will be harvested by seining and draining the water. The fish will be weighed as a group and then fish (200-300) will be sampled to obtain an average weight. Thirty fish from each pond will be processed to determine headed-gutted yield, fillet yield, and amount of visceral fat. Ten random fillets will be analyzed for body composition (fat, ash, protein, water). At the end of the study, data (weight gain, feed efficiency, survival, fillet composition, and fillet yield) will be subjected to statistical analysis. Differences between treatments will be considered significant at P < 0.05.
At the end of the six month study, there was no significant difference in the amount of food consumed or the amount of weight gained between the Control and Biomin® P.E.P. MGE fed fish. Food conversion ratio (FCR) was also similar between the two groups (2.1 vs 2.0). A FCR of 2.0 may seem high but is lower than the industry average of 2.8 for channel catfish. The net yield between the two groups was also similar (9,329 kg/ha vs 9,430 kg/ha). Survival was excellent between the Control and Biomin® P.E.P. MGE fed fish. The survival numbers presented in Table 1 are only an estimate and reflect only the fish that were counted as deceased.
The effect of Biomin® P.E.P. MGE on disease resistance in channel catfish is not clear as survival has been good in all of our studies. Feeding Biomin® P.E.P. MGE to catfish and challenging them with bacterial diseases may help in determining if there are any positive effects of Biomin® P.E.P. MGE on disease resistance.
The lack of a difference in feed intake and weight gain is surprising based on the results of our last tank study. In the present study, feed was blown out of a feed truck into 1-acre ponds by a trained feeder, similar to what you would find on a commercial catfish farm. ARS scientist went out and observed the feeder feed the fish on multiple occasions and he appeared to be doing a good job.
The processing results showed that carcass, fillet, and nugget yield was similar between the Control and Biomin® P.E.P. MGE fed fish. Fillet proximate analysis revealed that fillet fat was significantly lower (P = 0.0038) in fish fed Biomin® P.E.P. MGE (31.3% vs 35.9%) while fillet protein tended to be a little higher (62.4 vs 61.2) (P < 0.10). The amount of ash was similar between treatments. The observed lower amount of fat in the fillets of treated fish warrants further investigation.
Although the current study did not show any significant differences in performance characteristics between treated and untreated food-sized channel catfish, there was a significant reduction in the amount of fillet fat in the treated fish. This should be further explored as a reduction in fat could have positive benefits on fillet yield.