695
Husbandry/Management
It may be problem that under severe economic pressures the aquaculturist is tempted
to produce the maximum yield of fi sh in a fi nite volume of water, i.e. to use very
high stocking levels. Some sympathy must be directed towards the fi sh farmers
especially when prices paid for the stock are low and profi t margins are tight or
inadequate. The underlying problem is that within intensive cultivation systems, the
fi sh may be ‘stressed’ beyond the limit commensurate with the production of healthy
specimens. Interestingly, it has been suggested that reducing the stocking density
when water temperatures are high may well prevent some diseases, such as columnaris outbreaks in rainbow trout (Suomalainen et al. 2005 ). The outcome would be
that the lower stocking level leads to less disease, and more output. Stress may be
compounded by other inappropriate management practices in which aeration and
water fl ow are insuffi cient, overfeeding occurs, and hygiene declines below the
threshold at which disease is more likely to ensue. It may need only one diseased
individual to act as a reservoir of infection to the rest of the stock. Unsatisfactory
occurrences, which are readily controlled, include:
• the accumulation of organic matter, namely faecal material and uneaten fi sh
food, within the fi sh holding facilities, which allow the buildup of microbial
populations, some of which may cause disease. Also, such organic matter may
attract vermin, which may pose other health issues including the risk of human
disease, e.g. Weil’s disease/leptospirosis;
• the presence of dead fi sh in the tanks/ponds/cage/raceways for prolonged periods
(= bad sanitation). Again, the permits the increase in microbial populations as
well as contributing harmful chemicals to the water;
• the accumulation of a biofouling community, i.e. algae and slime, in the fi sh
tanks, and the problem associated with the collapse of blooms resulting in the
release of toxic materials;
• the depletion of the oxygen content of the water with a concomitant increase in
nitrogen levels, especially as ammonium salts;
• the lack of proper disinfection for items entering the fi sh holding facilities.
Reference is made here to nets, protective footwear, and size grading
machinery;
• lack of adequate sanitary disposal arrangements for dead fi sh, allowing access to
birds, e.g. seagulls, and vermin, and the build-up and spread of potentially harmful micro-organisms.
Good basic hygiene (water quality) and farm husbandry practices may successfully
alleviate many of the problems attributed to disease.
Farmed Fish
Husbandry/Management
It may be problem that under severe economic pressures the aquaculturist is tempted
to produce the maximum yield of fi sh in a fi nite volume of water, i.e. to use very
high stocking levels. Some sympathy must be directed towards the fi sh farmers
especially when prices paid for the stock are low and profi t margins are tight or
inadequate. The underlying problem is that within intensive cultivation systems, the
fi sh may be ‘stressed’ beyond the limit commensurate with the production of healthy
specimens. Interestingly, it has been suggested that reducing the stocking density
when water temperatures are high may well prevent some diseases, such as columnaris outbreaks in rainbow trout (Suomalainen et al. 2005 ). The outcome would be
that the lower stocking level leads to less disease, and more output. Stress may be
compounded by other inappropriate management practices in which aeration and
water fl ow are insuffi cient, overfeeding occurs, and hygiene declines below the
threshold at which disease is more likely to ensue. It may need only one diseased
individual to act as a reservoir of infection to the rest of the stock. Unsatisfactory
occurrences, which are readily controlled, include:
• the accumulation of organic matter, namely faecal material and uneaten fi sh
food, within the fi sh holding facilities, which allow the buildup of microbial
populations, some of which may cause disease. Also, such organic matter may
attract vermin, which may pose other health issues including the risk of human
disease, e.g. Weil’s disease/leptospirosis;
• the presence of dead fi sh in the tanks/ponds/cage/raceways for prolonged periods
(= bad sanitation). Again, the permits the increase in microbial populations as
well as contributing harmful chemicals to the water;
• the accumulation of a biofouling community, i.e. algae and slime, in the fi sh
tanks, and the problem associated with the collapse of blooms resulting in the
release of toxic materials;
• the depletion of the oxygen content of the water with a concomitant increase in
nitrogen levels, especially as ammonium salts;
• the lack of proper disinfection for items entering the fi sh holding facilities.
Reference is made here to nets, protective footwear, and size grading
machinery;
• lack of adequate sanitary disposal arrangements for dead fi sh, allowing access to
birds, e.g. seagulls, and vermin, and the build-up and spread of potentially harmful micro-organisms.
Good basic hygiene (water quality) and farm husbandry practices may successfully
alleviate many of the problems attributed to disease.
Farmed Fish