Bacterial impact on growth, health and disease of farmed Atlantic salmon and lumpfish

Despite considerable efforts to improve production with regard to animal welfare, disease control and sustainability in Norwegian aquaculture, both losses and feed conversion rate have not declined during the last 10 years. Lumpfish, used to control sea lice infestation in farmed Atlantic salmon, are lost to an even larger extent than Atlantic salmon. In both salmon and lumpfish, bacterial diseases are among the most important causes of death, and ulcer caused by bacteria contribute much to this. At the same time, new knowledge in both mammals and fish regarding the interaction between many bacteria and hosts and the good, probiotic effects of some bacteria, have shown that bacteria are important for increasing robustness, disease resistance and growth. A better understanding of the interaction between bacteria and between bacteria and eukaryotes will probably help to make living conditions that promote health, growth and sustainability. This thesis was initiated to investigate what impact adding potential probiotic bacteria to the two most abundant fish species in Norwegian aquaculture, lumpfish and Atlantic salmon has, and examine the effects regarding resistance to disease, survival and growth with an objective also to do some investigation regarding causality in bacterial diseases causing ulcer in Norwegian aquaculture. Tenacibaculum dicentrarchi was isolated from a natural disease outbreak in post-smolts. The bacteria were characterized by bacterial cultivation and Multi-locus Sequence Analysis (MLSA). The disease was reproduced in a challenge trial. This is the first time that T. dicentrarchi has been shown to cause disease in salmon in Norway. Bath treatment of Atlantic salmon by supplying probiotic Aliivibrio spp. (A. njordis NCIMB 42593 (VL1), A. balderis NCIMB 42592 (VL2) and A. nannie NCIMB 42594 (VL3)) to the rearing water indicated a significantly (p <0.05) lower mortality, greater resistance to natural Moritella viscosa infection, less ulcers, faster growth and better feed conversion rate. In lumpfish, bathing with the same probiotic bacteria indicated a significantly (p