Investigation of grilsification in farmed Atlantic salmon: Causes and management solutions
With the highly competitive nature of the North American marketplace, it is critical that salmon farm operations strive for the lowest unit cost of production possible. The formula for achieving this level of high performance from fish includes good husbandry and aggressive feeding strategies. One of the apparent side effects of such a formula is the increased frequency of early sexual maturation (grilsification) of a proportion of the salmon stock. These salmon (grilse) tend to be smaller, often with poorer flesh quality. Additionally, grilsification often compromises the health status of the fish, thereby making them more susceptible to disease. High levels of grilsing also impact on the farmer's flexibility in the marketplace, in that they have to market some of their fish in a very short time period. With an estimated gross revenue of $250 million this past year, losses due to grilsification are in the range of $25 - $50 million, making grilsing the single largest economic problem for salmon aquaculture in New Brunswick at the present time.
While it is generally acknowledged that the increased grilsing rate in farmed fish is primarily due to the aggressive feeding and growing strategy used by farms (early transfer of smolts, smolt size upon transfer, feed type and frequency), grilsing is also affected by environmental factors such as water temperature, and photoperiod. In addition, the presence of high and low grilsing families suggests that there is also a genetic component to grilsing. In the New Brunswick industry, the impact of early sexual maturation takes several forms:
- direct loss of value due to low quality flesh,
- loss of flesh weight due to gonadal development,
- impact on harvesting/marketing strategies (selling at inopportune times)
- losses due to increased mortality and disease.
This detailed investigation of the causes of grilsification will assist with the development of sound management practices to reduce the toll grilsing is taking on the local industry. This project has completed an industry survey of the factors associated with grilsing. Information related to feeding, photoperiod, smolt size and transfer date, sex, fat content, cage location, smolt origin/stock has been be gathered from six representative farms (over 500 cages in total) in NB and collated with grilsing levels. Coincident data has been gathered on biological and genetic markers in grilsing and non-grilsing fish. This data has included sex maturation hormones and immune system/genetic markers. Correlations are being made between these physiological and genetic data and grilsification.
2002 - 2004
Atlantic: Gulf of Maine, Scotian Shelf
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