Influence of feeding on the development of bacterial gill disease in rainbow trout Oncorhynchus mykiss

Abstract

Three trials were conducted to determine if feeding influenced the development of bacterial gill disease (BGD) in fingerling rainbow trout Oncorhynchus mykiss following bath exposure to Flavobacterium branchiophilum (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.

Blood chemistry and acid-base balance in rainbow trout Oncorhynchus mykiss with experimentally-induced acute bacterial gill disease

“…The marked lamellar hyperplasia associated with some of the more chronic BGD infections (Ostland et al 1990;Speare et al 1991a,b) that dramatically increases the diffusional distance, does not occur in the acute stages of the disease. Instead, there is mild to moderate swelling of lamellar pavement epithelium within the first 12 to 24h (MacPhee et al 1995). This could account for some increase in diffusional resistance across the gill lamellar epithelium, thereby contributing to a hypoxemia.…”

“…Previous work has shown that experimental challenge of rainbow trout with F. branchiophilum causes mortality and protracted morbidity only if the fish are fed (MacPhee et al 1995). Early attempts failed to produce BGD in fish while they were in the "fish boxes" because the fish would not take feed pellets, and thus we decided to use gastric feeding tubes.…”

“…The outer box was completely blackened. Water flow into the boxes was set at approximately 75 ml min -1 , a rate recommended by MacPhee et al (1995) for experimental BGD challenges. Room air was vigorously bubbled through air stones that were placed in the anterior part (cephalic end) of each box.…”

“…During the acute and peracute stages of BGD, natural and experimentally-infected trout normally show very little macroscopic or microscopic gill damage, despite often profound clinical disease MacPhee et al 1995). Because of this, and because of the usually rapid response to therapy (From 1980;Bullock 1990;Bullock et al 1991), it is hypothesized that the pathogenesis of BGD, at least initially, is largely the result of a reversible functional impairment of various gill processes, rather than of non-specific tissue damage, and that this impairment is initiated by chemical mediators, be they bacteria-, and/or hostderived.…”

Refining Feeding Practices for Hatchery Production of Siberian Sturgeon,Acipenser baeri

“…Additionally, larvae are not believed to be as adept as larger fish at locating feed; therefore, it has been a common practice to overfeed hatchery fish to ensure they are receiving adequate nutrition. Overfeeding increases systemic bacterial loading, the potential for gill infections (MacPhee et al 1995), and contributes to poor water quality (Faure and Labbe 2001). Siphoning excess feed can be extremely labor intensive and introduces risks of accidental damage to the fish during the siphoning process.…”