Effects of pre- and probiotics on pond production, growth and disease susceptibility of channel catfish Ictalurus punctatus and Nile tilapia Oreochromis niloticus
Type of Degreedissertation
Fisheries and Allied Aquacultures
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Disease outbreaks have become a major challenge to the profitable culture of fish and shellfish as aquaculture operations intensify. Globally, total annual losses from disease outbreaks have reached billions of United States dollars and have been identified as a threat to the sustainability of the industry. Costs, regulations, certification protocols and consumer preferences are driving the industry away from the use of therapeutic drugs towards the use of prebiotics and probiotics. This dissertation evaluated the effects of a prebiotic and probiotics under pond production conditions as well as the effects on growth and disease susceptibility under laboratory conditions. Four investigations were conducted. The first two examined the effects of two commercially-available probiotic products Lymnozyme® and PondToss™ as water additives in reducing mortality due to columnaris and improving pond water quality and pond production of channel catfish Ictalurus punctatus. Results from these two investigations lead to the evaluation of a prebiotic Previda® and some probiotic strains of Bacillus subtilis as feed additives in diets of Nile tilapia, Oreochromis niloticus. Hence, the third and fourth studies evaluated the effects of the prebiotic and probiotics and their combinations as feed additives on growth, immunity parameters and survival from Aeromonas hydrophila and Streptococcus iniae challenges in Nile tilapia Oreochromis niloticus. The effectiveness of the commercially-available aquatic probiotic product Lymnozyme® as a water additive to reduce mortality due to Flavobacterium columnare in juvenile channel catfish was assessed. Two experiments were conducted. In the first experiment, Lymnozyme® treatment was applied for 2 hours daily and in the second 8 hours daily. Mean cumulative mortalities from the first experiment were 77±15.4%, 76±8.9%, 69±11.2% and 64±7.6%, respectively, for control, and 3-, 7-, and 14-days of treatment with no significant difference between treatments (p=0.3179). In the second experiment, control fish had a significantly higher (p=0.0041) mean cumulative mortality (80±12.5%) than all treatments for 3, 7 and 14 days with mean mortalities of 61±14.5%, 50±13.0%, and 44±14.6%, respectively. The efficacy of using PondToss™ in ponds to improve water quality and pond production of channel catfish was evaluated over two production seasons (2011 and 2012). There was no significant treatment effects in mean total ammonia-nitrogen (TAN) and nitrite-nitrogen levels for untreated and treated ponds in both seasons (p=0.9130 in season 1, p=0.2131 for season 2). Water temperature, dissolved oxygen, pH, alkalinity, hardness and chloride levels were similar in all ponds (untreated and treated) for the two production years. Mean growth rate, percent survival, feed conversion ratio and mean weight at harvest in both production years showed no significant difference between treated and untreated ponds. Mean standing crops of 7,890±983kg/ha and 6,768±1294 kg/ha were obtained in 2011 with respect to treated and untreated ponds, while in 2012, mean standing crops were 9,060±620 kg/ha and 8,512±928 kg/ha for treated and untreated ponds, respectively. In either year, there was no significant treatment effects (p=0.2617 and 0.5604, respectively). The individual and combined effects of an 8-week feeding of diets containing two probiotic Bacillus subtilis strains (Aqua NZ and AP193) and the prebiotic Previda® on mean growth performance, immune parameters and Aeromonas hydrophila disease challenge in juvenile Nile tilapia were evaluated under laboratory conditions. None of the diets significantly improved growth performance (p=0.6972), respiratory burst activity (p=0.14) or lysozyme activity (p=0.32) of Nile tilapia. Except for the diet containing the prebiotic Previda® only (p=0.17), all other diets resulted in significantly lower mean cumulative fish mortality compared to the control (p<0.05). The combined effect of the prebiotic and probiotic strains showed a significant reduction in mortality from the prebiotic only diet. The 3-week (21 days) feeding effects of the probiotic strains SB3086, SB3295, SB3615, SB3086 + SB3615 and AP193 on mean growth, immune parameters and susceptibility to Streptococcus iniae infection in juvenile Nile tilapia produced no significant improvement in growth performance. Results from serum bactericidal activity showed a significant difference between treatment and control groups (p=0.0002), except the group fed probiotic strain SB3295 (p=0.5823). Lysozyme activity was also significantly higher in all treatments than control (p<0.0001). Mean cumulative mortalities were significantly lower in probiotic fed fish as compared to control (P≤0.0170). The combination of probiotic strains SB3086 and SB3615 did not appear to have any significant advantage in reducing mortality due to S. iniae in juvenile Nile tilapia. In conclusion, the prebiotic and probiotic strains used as water or feed additives in combination or individually effectively reduced disease mortality in channel catfish and Nile tilapia under laboratory conditions. Under production conditions in channel catfish ponds; however, PondToss™ was not significantly effective in improving water quality and growth.