PROBIOTICS AND FISH GROWTH
Heavy stocking, overuse of chemotherapeutics and general mismanagement of fish health have led to a need for alternative options to keep aquatic stock healthy. The period just after hatching is an important time for fishes as larvae are more susceptible to stressors. Probiotics are microbes that have been shown to improve fish immunity, gut health, growth and mitigate stress (Table 1). Prior research led by DSU has isolated several probiotic bacteria from the intestines of Fundulus heteroclitus and demonstrated their ability to inhibit growth of certain fish pathogens in disc diffusion assays. Because these probiotics were isolated from brackish water fish they may be useful for both marine and fresh water species. These probiotic bacteria will now be evaluated to see if they can enhance growth and survival of four commercially important finfish species, two marine (cobia and clownfish) and two freshwater (hybrid striped bass and rainbow trout). Each species will be tested in succession.
For each species trial, fish will be divided into 12 groups of ten larvae and placed in 2-L experimental containers with 1-L of water. Individual experimental containers will be randomly assigned to one of four treatments (three probiotics and an untreated control) allowing three replicates per treatment. Treatments will be applied by dosing the culture water with 106 CFU/ml of probiotic every other day.
Fish in the experimental containers will be fed a prepared diet selected for each individual fishes' size and nutritional requirements at a rate of 4% biomass per day. The daily ration will be divided into three feedings and the amount adjusted weekly. Water quality in the experimental containers will be checked daily, followed by a 50% water exchange.
After 30 days, surviving fish from each individual experimental container will be euthanized with an overdose of MS-222, counted, group weighed and measured for length. Growth and survival will be calculated and compared across treatments to ascertain which probiotic has the greatest impact on fish performance. Growth will be measured in calculated daily gains as well as relative weight gains. The experimental data will show which of the novel probiotics has the greatest impact on getting larvae through the high mortality post larval bottleneck period.