4 Interactions of Wild and Reared Fish and Invertebrates
141
under these circumstances (McGinnity et al. 1997) so that the growth and survival
of the marked fish may not accurately reflect the performance of the reared group,
in general.
However, the method has proved useful in tracking cod released for ranching in
Norwegian fjords (Jorstad et al. 1994) and more recently has been used to establish
that spawning of farmed cod in sea cages leads to the progeny of reared fish being
present adjacent to the cages which can disperse from these locations (Jorstad et al.
2006). Some combination of genetic tagging with robust statistical techniques for
individual assignment should provide increasingly powerful methods for tracking
reared individuals in the wild.
A more complicated and expensive, but ultimately far more informative, experimental
approach to investigating interactions is to set up “common-garden” experiments. These
have proved very useful in studying interactions in anadromous Atlantic salmon in
freshwater in Ireland (McGinnity et al. 2003), Norway (Fleming et al. 2000), Scotland
(Eric Verspoor, Freshwater Fisheries Services, Scottish Office, Pitlochry, Scotlandpersonal communication) and Spain (Carlos deLeaniz, University of Wales Swansea,
Wales- personal communication), and in the marine phase (Box 4.3). Most of these
experiments were carried out in a single site, where the performance of natives and an
imported strain or population (and sometimes the hybrids between them) were
compared. While it is recognised that the most comprehensive results would be obtained
using a reciprocal design, this has not proved economically or practically possible in
most situations. These experiments combined field ecology with molecular genetics. In
Norway and Scotland different groups were batch marked using different allozyme
genotypes or mitochondrial haplotypes, while in other experiments, VNTR screening
of broodstock and parental assignment were used to identify progeny to family, which
were then accumulated into the different groups (McGinnity et al. 1997). The difficulties
associated with conducting such experiments in “open” wild situations with European
marine species are exponentially greater, in that a reasonably restricted area, where the
test groups of wild and reared individuals can be compared, is required. None-the-less,
it may be possible to design such experiments using isolated or semi-wild situations,
with some degree of genetic or non-genetic (e.g., oxytetracycline bath) batch marking
of reared larvae and also parental assignment. The high information content of the
results from such experiments (e.g., in relation to adaptive differences and individual
variation), certainly justify the extra time and expense involved in their design and
execution.
Evaluation of susceptibility of bivalve molluscs to various pathogens has been
carried out in a number of field trials and the relative susceptibility of Irish and
European population of Ostrea edulis to Bonamia ostreae has been evaluated by
relaying the oysters in areas where the parasite is endemic (Culloty et al. 2004).
Resistance of Crassostrea virginca of different heritage to Perkinsus marinus has
been evaluated by comparing, for example, North Carolina and Chesapeake Bay
oysters, using standard tray culture conditions, at several sites in both regions
(Brown et al. 2005a). Furthermore, nine groups of oysters consisting of five
regional strains and four hybrid strains were evaluated at three sites within
141
under these circumstances (McGinnity et al. 1997) so that the growth and survival
of the marked fish may not accurately reflect the performance of the reared group,
in general.
However, the method has proved useful in tracking cod released for ranching in
Norwegian fjords (Jorstad et al. 1994) and more recently has been used to establish
that spawning of farmed cod in sea cages leads to the progeny of reared fish being
present adjacent to the cages which can disperse from these locations (Jorstad et al.
2006). Some combination of genetic tagging with robust statistical techniques for
individual assignment should provide increasingly powerful methods for tracking
reared individuals in the wild.
A more complicated and expensive, but ultimately far more informative, experimental
approach to investigating interactions is to set up “common-garden” experiments. These
have proved very useful in studying interactions in anadromous Atlantic salmon in
freshwater in Ireland (McGinnity et al. 2003), Norway (Fleming et al. 2000), Scotland
(Eric Verspoor, Freshwater Fisheries Services, Scottish Office, Pitlochry, Scotlandpersonal communication) and Spain (Carlos deLeaniz, University of Wales Swansea,
Wales- personal communication), and in the marine phase (Box 4.3). Most of these
experiments were carried out in a single site, where the performance of natives and an
imported strain or population (and sometimes the hybrids between them) were
compared. While it is recognised that the most comprehensive results would be obtained
using a reciprocal design, this has not proved economically or practically possible in
most situations. These experiments combined field ecology with molecular genetics. In
Norway and Scotland different groups were batch marked using different allozyme
genotypes or mitochondrial haplotypes, while in other experiments, VNTR screening
of broodstock and parental assignment were used to identify progeny to family, which
were then accumulated into the different groups (McGinnity et al. 1997). The difficulties
associated with conducting such experiments in “open” wild situations with European
marine species are exponentially greater, in that a reasonably restricted area, where the
test groups of wild and reared individuals can be compared, is required. None-the-less,
it may be possible to design such experiments using isolated or semi-wild situations,
with some degree of genetic or non-genetic (e.g., oxytetracycline bath) batch marking
of reared larvae and also parental assignment. The high information content of the
results from such experiments (e.g., in relation to adaptive differences and individual
variation), certainly justify the extra time and expense involved in their design and
execution.
Evaluation of susceptibility of bivalve molluscs to various pathogens has been
carried out in a number of field trials and the relative susceptibility of Irish and
European population of Ostrea edulis to Bonamia ostreae has been evaluated by
relaying the oysters in areas where the parasite is endemic (Culloty et al. 2004).
Resistance of Crassostrea virginca of different heritage to Perkinsus marinus has
been evaluated by comparing, for example, North Carolina and Chesapeake Bay
oysters, using standard tray culture conditions, at several sites in both regions
(Brown et al. 2005a). Furthermore, nine groups of oysters consisting of five
regional strains and four hybrid strains were evaluated at three sites within