168
E.J. Cook et al.
their uneven shells providing a large surface area for the attachment of cryptic
species. Biota may also reside in the mantle cavity, the gut or in various tissues.
During the early large-scale movements of oysters these associated species were
tolerated as a nuisance. However, with present knowledge and management such
releases are unlikely to be repeated on account of the wide range of microbiota and
syndromes that have been associated with such movements (Cheyney et al. 2000).
The movement of stock in seemingly small quantities can also have serious
consequences for native species. For example, the importation of Japanese eels
Anguilla japonica for cultivation trials in Europe released a rotund nematode that
in its final stage lodges in the visceral cavity near the air bladder and has caused
significant internal damage in other eel species such as the native freshwater eel
Anguilla anguilla (Kennedy and Fitch 1990). This nematode is easily dispersed by
copepods, and a wide range of paratenic hosts that include other fishes and insects.
The species has now become widely spread in Europe and the consequences for
the stock of the North Atlantic eel, already in decline, are unknown.
The spread of viral diseases through stock movements has been particularly
prevalent in Penaeid shrimp and has caused significant declines in production
(Subasinghe et al. 2000). Viruses may also be spread via other crustaceans, and
barnacles may even be capable of transmitting these to different countries as hull
fouling on ships. Pathogenic species may also be carried in the water and sediments
in the ballast tanks of ships and many species in commercial culture have been
found associated with hull fouling (Minchin and Gollasch 2002). No studies have
been undertaken on the potentially harmful biota carried on ships’ hulls although it
is suspected that the oyster disease Bonamia osteae was carried to different bays on
the hull of a barge (Howard 1994).
5.3.5 Genetic Impacts
Marine aquaculture species are increasingly being selected or modified with respect to
genetic traits linked to performance. Cross (2000) described the genetic improvement
of aquaculture species as an economic imperative and without it, the industry would
find it impossible to compete. For example, Coho salmon Oncorhynchus kisutch with
introduced growth hormone genes from Chinook salmon Oncorhynchus tshawytscha,
demonstrated much faster growth compared to the control group (Devlin et al. 1994).
Hybridization between the Yesso scallop Patinopecten (Mizuhopecten) yessoensis and
a local species Chlamys farreri have also been undertaken to improve growth performance (Yang et al. 2004; Yu et al. 2006). In addition, Chinese researchers have recently
introduced a new batch of Yesso scallop broodstock from Russia (Meng 2006) in an
effort to reconstruct their genetic diversity (Li and Xue 2005). These experiments have
produced new strains of scallops and some individuals have already been put out to
sea for a pilot grow-out.
As a result, a substantial fraction of genetic variation in aquaculture species resides
at a higher organisational level (among populations) than in natural populations
E.J. Cook et al.
their uneven shells providing a large surface area for the attachment of cryptic
species. Biota may also reside in the mantle cavity, the gut or in various tissues.
During the early large-scale movements of oysters these associated species were
tolerated as a nuisance. However, with present knowledge and management such
releases are unlikely to be repeated on account of the wide range of microbiota and
syndromes that have been associated with such movements (Cheyney et al. 2000).
The movement of stock in seemingly small quantities can also have serious
consequences for native species. For example, the importation of Japanese eels
Anguilla japonica for cultivation trials in Europe released a rotund nematode that
in its final stage lodges in the visceral cavity near the air bladder and has caused
significant internal damage in other eel species such as the native freshwater eel
Anguilla anguilla (Kennedy and Fitch 1990). This nematode is easily dispersed by
copepods, and a wide range of paratenic hosts that include other fishes and insects.
The species has now become widely spread in Europe and the consequences for
the stock of the North Atlantic eel, already in decline, are unknown.
The spread of viral diseases through stock movements has been particularly
prevalent in Penaeid shrimp and has caused significant declines in production
(Subasinghe et al. 2000). Viruses may also be spread via other crustaceans, and
barnacles may even be capable of transmitting these to different countries as hull
fouling on ships. Pathogenic species may also be carried in the water and sediments
in the ballast tanks of ships and many species in commercial culture have been
found associated with hull fouling (Minchin and Gollasch 2002). No studies have
been undertaken on the potentially harmful biota carried on ships’ hulls although it
is suspected that the oyster disease Bonamia osteae was carried to different bays on
the hull of a barge (Howard 1994).
5.3.5 Genetic Impacts
Marine aquaculture species are increasingly being selected or modified with respect to
genetic traits linked to performance. Cross (2000) described the genetic improvement
of aquaculture species as an economic imperative and without it, the industry would
find it impossible to compete. For example, Coho salmon Oncorhynchus kisutch with
introduced growth hormone genes from Chinook salmon Oncorhynchus tshawytscha,
demonstrated much faster growth compared to the control group (Devlin et al. 1994).
Hybridization between the Yesso scallop Patinopecten (Mizuhopecten) yessoensis and
a local species Chlamys farreri have also been undertaken to improve growth performance (Yang et al. 2004; Yu et al. 2006). In addition, Chinese researchers have recently
introduced a new batch of Yesso scallop broodstock from Russia (Meng 2006) in an
effort to reconstruct their genetic diversity (Li and Xue 2005). These experiments have
produced new strains of scallops and some individuals have already been put out to
sea for a pilot grow-out.
As a result, a substantial fraction of genetic variation in aquaculture species resides
at a higher organisational level (among populations) than in natural populations