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In too deep: The welfare of intensively farmed fish

CIWF report examining the welfare issues involved with intensive farming of fish.
Compassion in World Farming: Philip Lymbery


Intensive fish farming, whereby large numbers of fish are confined in a small area, causes serious welfare problems that need to be addressed urgently to prevent further widespread suffering.

Packed this tightly, these natural wanderers of the ocean swim as a group, or shoal, in incessant circles around the cage, like the pacing up and down of caged zoo animals. Fins and tails become worn and damaged as the fish rub against the cage sides or each other. The stress of crowding and confinement can manifest itself in increased susceptibility to disease.

The prevalence of fin and tail injuries, blinding cataracts, abnormal behaviours, disease outbreaks, serious infestation of salmon by sea lice, and high rates of mortality strongly indicate that current commercial stocking densities for farmed fish are too high. Maximum stocking densities of 10 kg/m3 for juvenile salmon at sea, and 20 kg/m3 for trout reared in freshwater should be introduced urgently through legislation.

Intensive farming has led to sea lice becoming the greatest single problem for farmed salmon in many areas. Sea lice are small parasitic crustaceans that feed on their host causing fish to lose skin and scales. Lice damage around the head can be so severe that the bone of the living fishes’ skull can be exposed.

Movement and transfer can be a frightening experience for fish, and has been described as causing “considerable” stress (Shepherd & Bromage, 1988). To protect fish welfare, transport times should be reduced to the absolute minimum. Water conditions for the fish in transit, such as oxygen levels, carbon dioxide, and pH, should be monitored at frequent intervals.

Farmed fish are normally starved for about 7-10 days before slaughter. It is said that this is to empty their gut and minimise the risk of the flesh becoming contaminated when gutted.