WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2023 51 (CONTINUED ON PAGE 52) Mozambique Tilapia — Probiotics and the Goldilocks Dose Our work at UNT-MCAPL began by using the single-strain probiotic Lactobacillus rhamnosus IMC 501 (Synbiotec, Camerino, Italy). Its use resulted in improvements in immunity and bone growth in the false percula clownfish Amphiprion ocellaris (Avella 2010). Results from experiments using this single-strain probiotic in Mozambique tilapia Oreochromis mossambicus, fed daily at five concentrations over a 28-d experimental period, resulted in a 30 percent increase in wet weight of juveniles compared to controls (Fig. 1A). This growth advantage continued for the four-week duration of the experiment and into grow-out stages (up to 250 days after the start of the experiment), continuing even after probiotics were discontinued (Anderson 2019). Although these results were encouraging, the manufacturer’s recommended dose of 5 × 1011 CFU/g did not result in the fastest growth rate, and higher growth rates were obtained by doubling the recommended dose to 10 × 1011 CFU/g. This finding is important for the farmer who must balance the cost of using supplements against potential gains associated with their use. Probiotic concentrations greater than 10 × 1011 CFU/g did not lead to further growth enhancement but to a slight decrease (Fig. 1 A, B). In short, for Mozambique tilapia juveniles, double the recommended dose of L. rhamnosus IMC 501 probiotics was just right — not too little and not too much. Red Drum — Probiotics and an American Beauty Encouraged by results with Mozambique tilapia, we investigated the effects of probiotics on red drum Sciaenops ocellatus. Red drum is one of the top-five aquaculture crops in Texas, with yearly harvests estimated at 90,718-104,326 t worth $6.9-7.3 million, helping to generate, with other species and aquatic plants, an estimated $349 million/yr economic impact on the state’s economy with jobs, feed and other economic benefits (Treece 2018). Red drum is also a favorite of the recreational fishery and has been stocked for many years, with 12 million red drum fingerlings produced in hatcheries stocked into Texas bays annually. We have been working with Jim Ekstrom, CEO, Ekstrom Enterprises and David Maus, Co-owner and Director of Copper Shoals Red Drum®, Ekstrom Aquaculture LLC, Palacios, TX, to help improve aquaculture sustainability and lower production costs. Reducing operating costs at the farm, finding substitutes for more affordable proteins in feeds, and/or increasing feed efficiency (by addition of supplements /probiotics) are needed to maintain profit margins. For red drum we used the multi-strain probiotic PrimaLac® (Star Labs, Clarksdale, Missouri, USA), consisting of four bacterial strains: L. acidophilus, L. casei, Bifidobacterium bifidium and Enterococcus faecium. PrimaLac® has a 30-yr history of improving growth and condition in terrestrial livestock and recently in shrimp and tilapia. Red drum feed was the same as that used at Ekstrom Aquaculture LLC: 44 percent crude protein, 15 percent crude fat, 3 percent crude fiber, 1 percent phosphorus and 12 percent ash. For juveniles, the smallest floating extruded feed, a 1.6 mm (1/16”) pellet size, from Rangen Inc. was used. Production and access to this probiotic feed for red drum was the outcome of a unique four-way collaboration between academia (UNT-MCAPL) and three industry partners: Star Labs, Rangen, Inc. and Ekstrom Aquaculture LLC, who supplied MCAPL with juvenile red drum over three years. Two treatment methods were used: 1) water-soluble, 2-percent PrimaLac® (WSP) was added directly to water and 2) a Probiotic Enhanced Starter Feed (PESF) was commercially formulated with the industry standard of 2 percent PrimaLac® (2 kg/t of feed) at the Rangen Inc. feed mill in Angleton, TX. PESF was fed to red drum juveniles at three levels: low, 3 percent of total fish mass; medium, 4 percent of total fish mass; high, 5 percent of total fish mass. These levels were designed to determine the effects of feeding rate, as well as the probiotics, on growth, mortality, condition and gut health. Results for both treatment types (WSP and PESF) were similar and showed significant (P < 0.05) increases in mean wet weight by 33 percent and improved (P < 0.05) FCE (mass gained/ feed consumed) for red drum juveniles after eight weeks of treatment (Busby 2021). Addition of PrimaLac® probiotics reduced aggressive behavior among fish and thus improved fish condition and health (Fig. 2). PrimaLac®-treated fish had significantly (P < 0.05) fewer incidences FIGURE 3. Relative abundance and percentages for microbial diversity in the small intestine for the eight most abundant phyla in juvenile red drum Sciaenops ocellatuss. Higher diversity occurs in fish intestines fed the probiotic (PrimaLac® ) compared to the control (no PrimaLac) treatments. WSP_C = Water Soluble Probiotic – Control (no PrimaLac®) and WSP_P = Water Soluble Probiotic (fish raised in 2% PrimaLac® dissolved in the water). See Busby (2021) for experimental details.
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