Four VT Papers Presented at Aquaculture America Meeting
Left: Dr. Steven R. Craig
Abstracts listed below:
1. Alternate Feedstuffs and Nutritional Strategies for Tilapia and Cobia
Steven R. Craig (
)
Two areas of interest at the Virginia Tech Aquaculture Center (VTAC) are organically certifiable replacement feedstuffs and the use of probiotics in conjunction with lower quality protein sources. The need to verify optimal inclusion rates for these new feedstuffs in dietary formulations, especially with respect to the higher level carnivores, is extremely important, as is their potential effects on final product quality. The use of probiotics to enhance digestive efficiencies is also a promising area of research. Inclusion of dietary probiotics might permit the use of feedstuffs previously considered inferior, or reduce the amount of dietary protein necessary for optimal production.
Research at VTAC has involved a certifiable protein source in diets for tilapia and cobia. In these trials, a standard experimental feed designed for tilapia, containing 38% crude protein and 8% lipid was used as a control diet. The other seven experimental diets were formulated so that NuProTM replaced the soybean meal component of dietary protein at levels of 20, 40, 60, 80 and 100%, with an additional diet containing solely NuProTM as the intact protein source. All these diets outperformed the control diet, with higher weight gain responses ranging from 9 to 35% above that experienced with the control diet. There were no significant differences in feed efficiency ratio values, or filet proximate composition. Trials are presently ongoing with cobia where eight experimental diets with NuProTM levels ranging from 10-100% of total dietary protein, are being fed to triplicate groups of juvenile cobia.
Research into probiotics at the VTAC is ongoing as well. In preliminary trials, an increase in weight gain was observed in tilapia fed diets with 0.05, 0.1 and 0.2% of a commercially available probiotic. A separate system was maintained with identical conditions utilizing the same control diet as in the “seeded” system. Over 9 weeks, the seeded control returned 1046% increase from initial weight compared with 844% from fish fed the same diet in the control system. In this same trial, fish fed a 32% crude protein diet supplemented with 0.05% of the probiotic in the seeded system had significantly higher weight gain than fish fed a 38% crude protein diet in the control system. Trials are underway to replicate these findings and investigate if further reductions in dietary protein can be achieved with probiotic addition without compromising production.
2. Transport of Juvenile Cobia
Jacqueline K. Zimmerman* and Michael H. Schwarz
Procedures and physical parameters used to transport 237 day-old live juvenile cobia (Rachycentron canadum) will be discussed. Included will be discussion related to transportation densities, gas saturations/management, pH, and ammonia levels. Implementation of these procedures resulted in 100% survival of 150g cobia after a total transport time of 20 hours covering over 1000 miles from The Gulf Coast Research Laboratory (GCRL) in Ocean Springs, MS to the Virginia Tech Seafood Agricultural Research and Extension Center in Hampton, VA. Additional relevant discussion will address other transport issues presently affecting fingerling shipment of this species.
3. Live Prey Size and Type as Factors in Cobia Larval Culture
Jacqueline
K. Zimmerman*, Michael H. Schwarz, David Mowry, Nick King
Virginia Tech’s ongoing cobia larviculture program combined efforts with INVE Aquaculture Nutrition to focus efforts on developing feeding regimes for cobia larviculture. Various combinations of live prey size and type (S and L rotifers, AF and EG Artemia nauplii) were evaluated with cobia larvae in recirculating systems to determine live prey preference as well as pinpoint key transitional stages historically associated with high mortality. Results on prey size, type, amounts consumed, and key observations on yolk sac, oil globule absorption, and fry performance will be presented along with relevant discussion.
4. Invited Paper - Mycobacteriosis: An Emerging Disease of Wild and
Cultured Fish with Zoonotic Potential
Stephen A. Smith
Fish mycobacteriosis, commonly known as “piscine tuberculosis”, is a progressively fatal local to systemic bacterial disease of wild and cultured fishes. The most commonly isolated species from fish are M. marinum, M. fortuitum, and M. piscium. To date, over 160 species of marine, brackish and freshwater fish have been found to be capable of being infected with these pathogens. Clinical signs in fish range from no clinical symptoms to ulcerated skin lesions to tumor-like nodules of the body and/or internal organs. Other clinical signs may include loss of scales, depigmentation or hyperpigmentation, emaciation, exophthalmia, fin and tail rot, abnormal swimming behavior, lethargy, cachexia, stunted growth and a generalized “wasting” syndrome. Internally, fish may have small, cream-white milliary nodules in any body organ or tissue, or may have generalized signs of a systemic bacterial infection. The internal organs most commonly affected are the spleen, kidney and liver, but the intestine, heart, gills, muscle and gonads may also be infected. Current diagnostic assays for fish mycobacteriosis involve culture of the bacteria on selective media, histological identification of the bacteria in tissue sections, and polymerase chain reaction analysis using fluids or tissues from the fish. In addition to causing morbidity and mortality in fish, these bacteria also have a zoonotic potential for humans. Infections in humans generally produce localized, cutaneous granulomas on the hands and arms commonly called “fish handlers disease” or “swimming pool granulomas”.
Chemotherapeutic treatment is not recommended for infections of mycobacteriosis in fish. Control of an outbreak is by culling infected individuals from a population or destruction of the entire population of fish to avoid the potential loss of investment, time and effort with a potentially infected group of fish, as well as, reducing the potential health risk to humans. Measures for avoiding infection in populations of fish should include pre-purchase diagnostic evaluation, regular fish health monitoring and possibly vaccines in the near future. Little is known about the efficacy of disinfectants on aquatic mycobacterial species. The most commonly recommended chemicals for mycobacterial disinfection (phenolics, glutaraldehyde) are toxic to animals and are not readily available outside a laboratory or hospital setting. To date, no disinfectants are specifically labeled or approved by the U.S. Environmental Protection Agency for use with food fish infected with mycobacteriosis. However, the use of either ethanol (75%) or sodium chlorite has been shown to be effective for disinfecting aquarium and aquaculture systems.
In addition to the oral presentations, the following Virginia Tech posters were presented at this year’s Aquaculture America meeting:
1. Development of Circular Sludge Collection Cones for Concentration of Solids in Raceways. Rasmussen, M.R., Lauresen, J., McLean, E., Craig, S.R.
2. An Economic and Business Analysis to Assist Aquaculture Producers make Strategic and Operation Decisions. Smith, S., Coale, C., Haugh, C.G., White, A., McLean, E.
3. Use of a Certified Organic Protein Source in Diets for Cobia Rachycentron canadum. Lunger, A., Schwarz, M.H., McLean, E., Craig, S.R.
4. Impact of Supplemental Internal Structures upon Hydrodynamic Performance of Commercial Trout Tanks for use in Flatfish Culture. Rasmussen, M.R., McLean, E.
5. Influence of Stocking Density upon Fluid Dynamics in a Recirculating Aquaculture System. Rasmussen, M.R., McLean, E., Craig, S.R.
6. Comparison of two Different Methods for Evaluating the Hydrodynamic Performance of an Industrial-scale Fish-rearing Unit. Rasmussen, M.R., McLean, E., Craig, S.R.
7. The Effect of Tank Color upon Growth Performance and Stress Response of Summer Flounder, Paralichthys dentatus. Cotter, P.A., Harris, J.O., McLean, E., Craig, S.R., Schwarz, M.H., Rasmussen, M.R.
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