4 Interactions of Wild and Reared Fish and Invertebrates
137
4.5 Consequences of Interactions
4.5.1 Direct Effects
Following direct interactions it is likely that hybrid progeny of interbreeding between
farm and wild strains, as well as “pure” parental types, will result. The proportions of
each of these types among first generation progeny will depend on the relative proportion of wild and reared parents, the relative spawning success of each sex of each type
and, ultimately, the relative fitness of parental types and hybrids (with either type as
dam and sire). The various field experiments with Atlantic salmon in Ireland and
Norway have shown a trend for graduated spawning success and reproductive fitness;
highest in pure wild, intermediate values in hybrids and lowest in reared (Einum &
Fleming 1997; McGinnity et al. 1997, 2003; Fleming et al. 2000). Assuming that this
is a general trend in interactions between wild populations and reared strains of most
species, then following a single reared incursion, reared influence in the wild will
gradually decrease over generations albeit at the expense of reduced fitness in this
period. However it is recognised that incursions will usually be continuous, i.e., there
and Norway. In the Burrishoole river system in the west of Ireland, longstanding ranching and nearby sea cage farming occur alongside native
salmonid populations.
Using archival scales, statistically significant changes in gene diversity
occurred at the MH class I marker over time in wild S. trutta, but no changes
were observed at neutral microsatellite loci (Coughlan et al. 2006). In an
experimental natural stream in the same system, eyed eggs from native
salmon and salmon from a neighbouring river (derived from wild broodstock
and only retained in the hatchery until eyed egg stage) were introduced.
Significant selective effects were evident at MH class II after eight months in
freshwater, in the non-native population, but not in natives. No significant
results were observed in either group at the MH class I locus or at eight
neutral microsatellite loci (deEyto et al. 2007). Thus, it appears that variation
at MH loci may be a feature of local adaptation, as well as influencing
survival in native trout when challenged by diseases carried by reared salmon.
Therefore, reared salmon may negatively impact on wild salmonid populations, putatively via disease transmission, in addition to having direct and
other indirect genetic effects (McGinnity et al. 2003).
These data, demonstrating another way that aquaculture practices can
detrimentally effect wild salmonid populations, suggest that further studies of
such interactions in the context of fish immunity (e.g., MHC genes) and
disease prevalence are required. Similar, MHC-based studies in other teleost
species subjected to aquaculture are also advisable.
137
4.5 Consequences of Interactions
4.5.1 Direct Effects
Following direct interactions it is likely that hybrid progeny of interbreeding between
farm and wild strains, as well as “pure” parental types, will result. The proportions of
each of these types among first generation progeny will depend on the relative proportion of wild and reared parents, the relative spawning success of each sex of each type
and, ultimately, the relative fitness of parental types and hybrids (with either type as
dam and sire). The various field experiments with Atlantic salmon in Ireland and
Norway have shown a trend for graduated spawning success and reproductive fitness;
highest in pure wild, intermediate values in hybrids and lowest in reared (Einum &
Fleming 1997; McGinnity et al. 1997, 2003; Fleming et al. 2000). Assuming that this
is a general trend in interactions between wild populations and reared strains of most
species, then following a single reared incursion, reared influence in the wild will
gradually decrease over generations albeit at the expense of reduced fitness in this
period. However it is recognised that incursions will usually be continuous, i.e., there
and Norway. In the Burrishoole river system in the west of Ireland, longstanding ranching and nearby sea cage farming occur alongside native
salmonid populations.
Using archival scales, statistically significant changes in gene diversity
occurred at the MH class I marker over time in wild S. trutta, but no changes
were observed at neutral microsatellite loci (Coughlan et al. 2006). In an
experimental natural stream in the same system, eyed eggs from native
salmon and salmon from a neighbouring river (derived from wild broodstock
and only retained in the hatchery until eyed egg stage) were introduced.
Significant selective effects were evident at MH class II after eight months in
freshwater, in the non-native population, but not in natives. No significant
results were observed in either group at the MH class I locus or at eight
neutral microsatellite loci (deEyto et al. 2007). Thus, it appears that variation
at MH loci may be a feature of local adaptation, as well as influencing
survival in native trout when challenged by diseases carried by reared salmon.
Therefore, reared salmon may negatively impact on wild salmonid populations, putatively via disease transmission, in addition to having direct and
other indirect genetic effects (McGinnity et al. 2003).
These data, demonstrating another way that aquaculture practices can
detrimentally effect wild salmonid populations, suggest that further studies of
such interactions in the context of fish immunity (e.g., MHC genes) and
disease prevalence are required. Similar, MHC-based studies in other teleost
species subjected to aquaculture are also advisable.