Experimental infection of eggs and yolk sac larvae of halibut, Hippoglossus hippoglossus L.

Abstract

Scanning electron micrographs of halibut eggs with an epiflora dominated by Flexibacter sp., showed ulcerations colonized by large numbers of bacteria. The chorion was dissolved in most ulcerations and the zona radiata was severely damaged. Infection experiments showed that exposure to these bacteria caused high mortalities at the late egg stage, hatching and the early yolk sac stage. Eggs exposed to three different Vibrio spp. showed different mortality patterns, with low mortality at hatching, followed by a eontinuous high mortality throughout the yolk sac stage. Mortality in the uninfected control group was low throughout the experiment. Transmission electron microscopy of the l''/7>no-infccted larvae showed baeteria present in the gill, heart and frontal yolk sae regions.

Diseases, prophylaxis and treatment of the Atlantic halibut Hippoglossus hippoglossus: a review

“…It resembles the fish pathogen Flexibacter maritimus, but differs from the latter in a number of biochemical and physiological characteristics. Challenge experiments confirmed that this bacterium is capable of causing mortality in halibut eggs and yolk-sac larvae by penetrating the eggshell (Bergh et al 1992b). It has not been found on hosts other than halibut, despite its ability to cause mortality in the eggs and larvae of cod Gadus morhua (Bergh 2000).…”

“…In general, the incidence of gaping-jaw larvae increases with increasing temperature (Pittman et al 1989(Pittman et al , 1990a, an environmental factor that might cause increased bacterial activity and increase larval swimming activity. However, it should be noted that the gaping jaw condition is not related to the total number of bacteria in the rearing water (Opstad & Bergh 1993 (Bergh et al 1992b(Bergh et al , 1997. The exact nature of the gaping jaw syndrome remains unresolved.…”

“…Thus, since the early 1990s, the amount of experience and knowledge of diseases of viral, bacterial or parasitical etiology of the Atlantic halibut has grown significantly. The evidence for the importance of diseases that affect the early life stages, such as infections by birnaviruses (Biering et al 1994), nodaviruses (Grotmol et al 1995(Grotmol et al , 1997, or various opportunistic bacteria (Bergh et al 1992b) has now been demonstrated by different challenge experiments (Table 1).The parasite fauna of wild Atlantic halibut have not been widely studied, for which reason our knowledge of potential harmful parasites in farmed fish is limited. Studies of parasites on wild halibut have mainly concentrated on describing metazoan parasites, particularly helminths (e.g.…”

“…In principle, this prophylactic treatment establishes a hygiene barrier between the rearing water of the broodstock fish, including ovarian fluid, and the rearing water of the larvae, by killing extraovulary organisms. Epibiotic bacteria grow on the surface of halibut eggs (Hansen & Olafsen 1989), and some of them may be pathogens (Bergh et al 1992b, Hansen et al 1992. By killing the epiflora, 69 Dis Aquat Org 48: [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74] 2001 their ability to accumulate to a level which may be harmful to the eggs is blocked, and the possibility that certain species of epiflora may infect the larvae posthatch is avoided.…”

Use of Probiotics in Aquaculture

“…Bergh and colleagues [22] observed that, when starting its first feeding, the intestinal flora of the Atlantic halibut (Hippoglossus hippoglossus) changed from a prevalence of Flavobacterium spp. to Aeromonas spp./Vibrio spp.…”