Probiotic Effects of a Novel Strain, Acinetobacter KU011TH, on the Growth Performance, Immune Responses, and Resistance against Aeromonas hydrophila of Bighead Catfish (Clarias macrocephalus Günther, 1864).

Anurak Bunnoy,Uthairat Na-Nakorn,Prapansak Srisapoome

doi:10.3390/microorganisms7120613

Abstract

In the present study, the novel probiotic strain Acinetobacter KU011TH with an evident lack of pathogenicity in catfish was experimented. Three practical administration routes, namely, feed additive (FD), water-soluble additive (SOL), and a combination route (FD+SOL), were applied in two sizes of catfish. After 120 days of FD+SOL administration, catfish fingerlings (15 g) exhibited a significant improvement in all tested growth performance parameters. For 15- and 30-day applications at the juvenile stage (150 g), phagocytic activity, phagocytic index, lysozyme activity, respiratory burst activity, alternative complement pathway, and bactericidal activity were significantly increased. Furthermore, probiotic-administered bighead catfish exhibited an upregulated expression of several immune-related genes in tested organs. Significant colonization by Acinetobacter KU011TH in rearing water and on skin and gills was observed among experimental groups. Histological analysis clearly indicated enhanced physical characteristics of skin mucosal immunity in the treated groups. No histopathological changes in the gills, skin, intestine or liver were observed among the fish groups. Interestingly, after challenge with Aeromonas hydrophila, the survival rates of the treated groups were significantly higher than those of the controls. In conclusion, the novel probiont Acinetobacter KU011TH provides a potent strategy for improvement in growth and disease resistance, which is an important steppingstone for sustaining catfish aquaculture.

Highlights

In Thailand, catfish farming has been growing at an impressive rate in recent decades
Research on the genus Acinetobacter has been focused on some species that have effects on human health, especially A. baumannii, the beneficial effects of most of the remaining species on their hosts have never been addressed to date
When considered together with pathogen challenge, the data clearly showed that the combination of water supplemented with 103 colony-forming units (CFU)/mL and feed supplemented with1 × 103, 1 × 105 and1 × 107 CFU/kg diet effectively enhanced catfish resistance against the harmful pathogen. These results suggested that water-soluble application of the viable probiotic at concentrations ranging from 1 × 103–105 CFU/mL at three-day intervals for 30 days is sufficient to elevate the catfish immune system to safeguard the fish from A. hydrophila infection

Summary

Introduction

In Thailand, catfish farming has been growing at an impressive rate in recent decades. The bighead catfish (Clarias macrocephalus Günther, 1864), known as broadhead catfish or “pla-duk-uey” in Thai, is an economically important cultured species in Southeast Asia, especially Thailand. Hybrid catfish have demonstrated many commercially desirable characteristics, such as rapid growth; increased feed conversion, resistance to infectious diseases, and overall survival, as well as their tolerance to a wide range of environmental conditions. As a consequence, these fish have attained a remarkable market value in production and export among the fish and fishery products of Thailand [2,3]. Interest in alternative disease control strategies, including nonspecific immunostimulants, vaccines, nutritional supplements, phytochemical products, and probiotics, has been increasing in the global aquaculture industry during the last decade [7]

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