Farm-raised salmon is the highest valued seafood product in British Columbia (BC) and is the province’s top agricultural export. In 2019, the salmon farming industry generated over $1.6 billion in total revenue and supported over 6,000 jobs. Recently, however, salmon aquaculture companies in BC have experienced fish mortalities due to gill disorders and mouth lesions that have cost the companies substantial revenue. Many potential causes such as viruses, bacteria, parasites, and harmful-algae blooms have been examined extensively and ruled out as causative agents. The present hypothesis is that the removal of biofouling communities on the salmon nets via power-washing creates suspended particulate matter that impacts fish-gill health. Hydrozoans, with their stinging cells, are the most likely problematic species. They have been shown to cause gill disorders and mouth lesions in previous European laboratory-based studies and are known to occur in biofouling communities at BC salmon farms.
This study examined the development of biofouling communities on nets at two commercial Atlantic salmon (Salmo salar) farms on Vancouver Island (BC), with a focus on identification and quantification of the various species. Five 30 x 30-cm fish-net panels were deployed at each of five depths (1, 5, 10, 15, and 20 m), totalling 25 panels per site. These panels were collected bi-weekly, with fresh panels being re-deployed, for approximately six months. Their collection occurred just before commercial net cleaning. Species growing on the nets were identified and quantified, with an emphasis on hydrozoan identification. Key environmental parameters (e.g. temperature, salinity, dissolved oxygen, pH, nitrates, ammonia, phosphates, iron, and silica) were measured daily. The gill health of fish contained within the study pens was monitored weekly for the duration of the study. The relationship between the environmental parameters, the biofouling community, and fish-gill health will be examined by various correlative statistical techniques.
Results show seasonal/site patterns of the environmental parameters, seasonal/site/depth variations in the biomass of various species in the biofouling community, and seasonal trends in individual gill scores of the fish sampled. Specific results will be discussed. These data will be used to explore interactions between the environmental variables and the biofouling community and between the biofouling community and gill health.