Does Carnobacterium divergens isolated from Atlantic salmon, Salmo salar L., colonize the gut of early developing turbot, Scophthalmus maximus L., larvae?

Abstract

It is well established from endothermic animals that the adhesion of lactic acid bacteria involves host speci®city (Fuller 1986). In juvenile ®sh, JoEborn, Olsson, Westerdahl, Conway & Kjellberg (1997) reported by in vitro tests that a Carnobacterium sp. isolated from Atlantic salmon, Salmo salar L., colonized the gastrointestinal tract of rainbow trout, Onchorynchus mykiss (Walbaum). However, no information from ®sh larvae is available on whether the adhesion of lactic acid bacteria involves host speci®city. This is relevant in the context of whether or not it is possible to colonize the gastrointestinal tract of larvae at early stages with probiotics, notably Gram-positive bacteria, such as lactic acid bacteria, or by a resident micro ora, which may contribute to nutrition. The following bacteria were used in the present study: Vibrio pelagius isolated from copepod-fed turbot, Scophthalmus maximus L., larvae (Munro, Barbour & Birkbeck 1994), which is unusual in that it contains the polyunsaturated fatty acid eicosapentaenoic acid (20:5 n-3) (Ringu, Sinclair, Birkbeck & Barbour 1992), and a lactic acid bacterium, Carnobacterium divergens, isolated from Atlantic salmon. The main reason for using this species was that it produced a substance that inhibited the growth of both Vibrio anguillarum and Proteus vulgaris (Strum 1988), and Aeromonas salmonicida (Ringu 1999). Recently, colonization of different bacterial strains in larval turbot was determined using an enzyme-linked immunosorbent assay (ELISA) (Ringu, Birkbeck, Munro, Vadstein & Hjelmeland 1996; Ringu & Vadstein 1998). The purpose of the current study, was to evaluate whether a C. divergens, orginally isolated from Atlantic salmon, was able to colonize the gut of turbot larvae by adding this bacterial species to the rearing water and to compare these results with those for larvae exposed to V. pelagius, by using the ELISA method. Furthermore, a previous study (Ringu et al. 1996) demonstrated that antisera used in ELISA showed high sensitivity against homologous bacterial antigens and very little crossreaction with heterologous bacteria. Turbot eggs were obtained from Tinfos Aqua, Norway, and 1000 eggs were incubated in 80-L circular tanks with at bottoms in static water. A detailed description of larval rearing conditions and cultivation of live feed (Brachionus plicatilis SINTEFstrain) is given by Ringu et al. (1996). The following bacterial strains were used: C. divergens, originally isolated from young Atlantic salmon juveniles (Strum 1988); and Vibrio pelagius, isolated from copepod-fed turbot larvae (Munro et al. 1994). Vibrio pelagius was identi®ed as described by Munro et al. (1994) using the `Bacterial Identi®er' program (Bryant, Lee, West & Colwell 1986). Carnobacterium divergens was identi®ed using carboR