4 Interactions of Wild and Reared Fish and Invertebrates
143
4.7 Methods to Reduce Such Effects
4.7.1 Induction of Sterility/Triploidy
Induction of sterility in reared strains of fish and invertebrates has been extensively
investigated in conjunction with the aquaculture industry, because in many species
both appearance and flesh quality deteriorates greatly at sexual maturity. In certain
species, such as gadoid and pleuronectid fish, males tend to mature younger and at
a much smaller size, leading to an interest in all female production. Sterility would
also be desirable in animals that might escape from rearing facilities or in
commercial ranching (although, obviously where the object of stocking is to
produce or enhance self-sustaining populations, sterility would not be desirable).
Sterility can be achieved directly by hormonal treatment although this is
recommended against in certain regions, and triploidy, induced by temperature or
pressure shock in fish or by chemical means in shellfish, is an alternative. In certain
fish species (e.g., salmonids) male triploids have a weak reproductive capability
and sex reversal has to be achieved in the female parent (converted to a so-called
pseudo male) by hormonal means. All-female production is possible in salmonids
because the female is the homogametic sex. Objections have been raised to sterile
fish production in salmon ranching since it is not clear whether the process will
inhibit freshwater migration. Furthermore, induction of triploidy seems to inhibit
some aspects of physiological performance, such as reduced tolerance of low
oxygen conditions. Since these conditions pertain in cage farming during sea louse
In this experiment, 0+parr from the Owenmore river showed substantial
downstream migration, which was not shown by native and ranched parr.
This appears to have been an active migration rather than competitive displacement and may reflect an adaptation to environmental or physiographic
conditions within the Owenmore River catchment, where the main nursery
habitat is downstream of the spawning area. There were no differences
between native and ranched in smolt output or adult return. Both of these
measures, however, were significantly lower for the non-native group.
A greater proportion of the non-native Atlantic salmon was taken in the
coastal drift nets compared to the return to the Burrishoole system, probably
as a result of the greater size of the non-native fish. The overall lifetime success of the non-native group, from fertilized egg to returning adult, was some
35% of native and ranched. The ranched group showed a significantly greater
male parr maturity, a greater proportion of 1-year-old smolts, and differences
in sex ratio and timing of freshwater entry of returning adults compared to
natives, which may have fitness implications under specific conditions.
143
4.7 Methods to Reduce Such Effects
4.7.1 Induction of Sterility/Triploidy
Induction of sterility in reared strains of fish and invertebrates has been extensively
investigated in conjunction with the aquaculture industry, because in many species
both appearance and flesh quality deteriorates greatly at sexual maturity. In certain
species, such as gadoid and pleuronectid fish, males tend to mature younger and at
a much smaller size, leading to an interest in all female production. Sterility would
also be desirable in animals that might escape from rearing facilities or in
commercial ranching (although, obviously where the object of stocking is to
produce or enhance self-sustaining populations, sterility would not be desirable).
Sterility can be achieved directly by hormonal treatment although this is
recommended against in certain regions, and triploidy, induced by temperature or
pressure shock in fish or by chemical means in shellfish, is an alternative. In certain
fish species (e.g., salmonids) male triploids have a weak reproductive capability
and sex reversal has to be achieved in the female parent (converted to a so-called
pseudo male) by hormonal means. All-female production is possible in salmonids
because the female is the homogametic sex. Objections have been raised to sterile
fish production in salmon ranching since it is not clear whether the process will
inhibit freshwater migration. Furthermore, induction of triploidy seems to inhibit
some aspects of physiological performance, such as reduced tolerance of low
oxygen conditions. Since these conditions pertain in cage farming during sea louse
In this experiment, 0+parr from the Owenmore river showed substantial
downstream migration, which was not shown by native and ranched parr.
This appears to have been an active migration rather than competitive displacement and may reflect an adaptation to environmental or physiographic
conditions within the Owenmore River catchment, where the main nursery
habitat is downstream of the spawning area. There were no differences
between native and ranched in smolt output or adult return. Both of these
measures, however, were significantly lower for the non-native group.
A greater proportion of the non-native Atlantic salmon was taken in the
coastal drift nets compared to the return to the Burrishoole system, probably
as a result of the greater size of the non-native fish. The overall lifetime success of the non-native group, from fertilized egg to returning adult, was some
35% of native and ranched. The ranched group showed a significantly greater
male parr maturity, a greater proportion of 1-year-old smolts, and differences
in sex ratio and timing of freshwater entry of returning adults compared to
natives, which may have fitness implications under specific conditions.