The Influence of the Probiotic PondToss™ on Growth Performance and Health of Channel Catfish, Ictalurus Punctatus, And Nile Tilapia, Oreochromis Niloticus

Abstract

In 2011, global aquaculture production of food fish comprising channel catfish and Nile tilapia reached 62.7 million tonnes with an estimated value of US$ 130 billion. As aquaculture technology intensifies to meet market demands, the economic losses in the aquaculture industry from bacterial diseases continue to grow. Of those bacterial diseases, columnaris has been reported as one of the major causes of massive economic losses in channel catfish and Nile tilapia farming. In the search for alternative environmentally-friendly treatments, probiotics have been suggested as possible alternatives to chemotherapeutants and antibiotics. Towards this goal, this research evaluated the effects of the commercially-available probiotics as a feed additive on channel catfish and Nile tilapia growth performance and protection against columnaris (Flavobacterium columnare) under laboratory conditions. The first study was conducted to evaluate the influence of the probiotic product PondToss™ on growth performance and survival of the juvenile Nile tilapia Oreochromis niloticus and its potential to reduce mortality when challenged with Flavobacterium columnare. The study was carried out in two phases, growth phase and disease challenge phase. The growth phase was designed for feeding a control or probiotic (0.1% PondTossTM at 5.9×107CFU/g of feed or 0.2% PondTossTM at 1.2×108 CFU/g of feed) diet in a flow-through system for 56 days. The results at the end of this study demonstrated that addition of PondTossTM to the feeds at these rates did not significantly improve mean final body weight (p=0.4297) which was 35.3 ± 1.6 g, 35.2 ± 1.3g, and 34.5 ± 1.7g for control, .1% PondTossTM and 0.2% PondTossTM, respectively. Mean percent weight gain (p=0.1159) was 930.4 ± 66.7%, 949.9 ± 41.6%, and 903.1 ± 49.5% for control, 0.1% PondTossTM and 0.2% PondTossTM, respectively. Specific growth rates (p=0.0838) were 4.12 ± 0.09 % day-1, 4.12 ± 0.06% day-1, and 4.06 ± 0.05% day-1 for control, 0.1% PondTossTM and 0.2% PondTossTM, respectively. Feed conversion ratio (p=0.7052) was 1.12 ± 0.04, 1.11 ± 0.01, and 1.12 ± 0.02 for control, 0.1% PondTossTM and 0.2% PondTossTM, respectively. Mean survival rates (%) (p=0.1711) were 98.2 ± 1.5%, 96.2 ± 3.5% and 97.2 ± 3.5% for control, 0.1% PondTossTM and 0.2% PondTossTM respectively. Fish from all replicates of a treatment were pooled and then randomly assigned to one of six treatments: C1 (Control fish fed Control feed), C2 (Fish from Control fed PondToss™ at 5.9×107 CFU/g), C3 (Fish from 0.1% PondToss™ now fed Control feed), C4 (Fish from 0.1% PondToss™ now fed 0.1% PondToss™ at 5.9×107 CFU/g), C5 (Fish from 0.2% PondToss™ now fed Control feed) and C6 (Fish from 0.2% PondToss™ now fed 0.2% PondToss™ at 1.2×108 CFU/g). All fish were fed their original diet until post-challenge when new feeds were fed. Fish were then challenged with F. columnare strain ALG-530 by immersion at a dosage of 1.4 x 106 CFU/mL. None of the fish were negatively impacted or experienced mortality. The failure to induce an outbreak of columnaris in all treatments could have been related to environmental conditions of the study, pre-exposure to F. columnare, or issues related to the F. columnare virulence or infection mode. Regardless, no conclusion could be made about potential benefits of PondToss™ in reducing mortalities related to columnaris in Nile tilapia fingerlings.

The second study was conducted to evaluate the influence of PondTossTM on growth performance and survival of channel catfish, Ictalurus punctatus, fingerlings and its potential effect on their survival when challenged with F. columnare ALG-530. The study was again carried out in two phases-growth phase and disease challenge phase. The growth phase was designed for feeding a control or probiotic (1% PondToss™ at: 4.1×107 CFU/g or 2% PondToss™ at 6.9×107 CFU/g of feed) diet in a flow-through system for 52 days. The results at the end of the study showed that under the conditions of the present trial, none of the diets significantly improved mean final body weight (FBW, CONTROL: 36.2 ± 2.5 g, 1% PONDTOSS™:34.5 ± 2.1 g, 2% PONDTOSS™: 35.0 ± 1.9 g), percent weight gain (%WG, CONTROL: 351.1 ± 30.3%, 1% PONDTOSS™: 334.9 ± 28.4%, 2% PONDTOSS™: 339.8 ± 22.2%), specific growth rate (SGR, CONTROL: 2.9 ± 0.1% day-1, 1% PONDTOSS™: 2.82 ± 0.1% day-1, 2% PONDTOSS™: 2.8 ± 0.1% day-1), feed conversion ratio (FCR, CONTROL: 1.2 ± 0.2, 1% PONDTOSS™: 1.2 ± 0.1, 2% PONDTOSS™: 1.1 ± 0.1), and survival rate (SV: CONTROL: 76.4 ± 23.1%, 1% PONDTOSS™: 86.4 ± 24.6% and 2% PONDTOSS™: 87.2 ± 27.2%). In the challenge phase, fish from each treatment in Phase 1 were combined and then randomly assigned to one of six treatments: C1 (Fish from Control fed Control feed), C2 (Fish from Control fed 1% PondToss™), C3 (Fish from 1% PondToss™ fed Control feed), C4 (Fish from 1% PondToss™ fed 1%PondToss™), C5 (Fish from 2% PondToss™ fed Control feed) and C6 (Fish from 2% PondToss™ fed 2%PondToss™). Fish were then challenged with F. columnare strain ALG-530 (3.4 ×106 CFU/mL) by immersion based upon doses determined during the pre-challenge study. The fish were exposed to the bacteria in static water for 6 hours and monitored for 20 days after the challenge. All dead and moribund fish were removed and counted. Moribund and freshly dead fish were collected and isolated for bacterial recovery and confirmation. Under this study condition, the treatments had no significant effects on mean mortalities compared to the control. Because of the limited number of fish available for the challenge study, fish losses within each treatment replicate resulted in large changes in mortality rates leading to high within treatment variability and non-significant differences. Regardless, no significant benefit or general trends were observed when using PondTossTM as a feed additive in reducing mortalities related to columnaris infection. In conclusion, PondTossTM used as a feed additive did not significantly enhance growth, FCR or survival of Nile tilapia or channel catfish fingerlings under the given experimental conditions. Likewise, challenges with F. columnare did not show any reduction in mortalities when using PondTossTM as a feed additive at the experimental dosages, either before or after challenge, for juvenile channel catfish and were inconclusive for juvenile Nile tilapia. Because columnaris typically infects fish from the outside through gills and skin and then becomes systemic, a better approach to using probiotics like PondTossTM might be via water application.