ABSTRACT: Three trials were conducted to determine if feeding influenced the development of bacterial gill disease (BGD) in fingerling rainbow trout Oncorhynchusmykiss following bath exposure to Flavobacteriumbranchiophilum (LAB 4a). In each trial (Trial 1, n = 70 x 3; Trial 2, n = 140 x 3; Trial 3, n = 250 x 3), the comparison groups (fed, unfed, negative controls) were held in similar conditions and (where applicable) fed prior to exposure to the pathogen. Severe clinical signs and high rates of mortality developed within 24 h in fish which were provided feed following the bath exposure. Cumulative mortalities ranged from 43 to 63% by 12 d post-exposure. Unfed fish demonstrated only mild and transient clinical signs of BGD, and cumulative mortalities of 0 to 2% 12 d post-exposure. In one trial, resumption of feeding 6 d post-exposure resulted in 26% cumulative mortality within 7 d. Estimation of the quantity of F. branchiophilum antigen by enzyme-linked immunosorbent assay (ELISA) indicated that feeding facilitated colonization of the gill. The evaluation of water quality and direct observations suggest that the influence of feeding on BGD is linked to the consumption of feed by the fish, rather than to environmental changes arising from feeding. Alterations in the unstirred layer on the gill, secondary to feed consumption and waste excretion, may aid bacterial colonization.

KEY WORDS: Mucosal . Colonization . Respiration . Excretion

Published in DAO Vol. 21, No. 3 (1995) on March 30
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1995