ABSTRACT
Transgenic channel catfish (Ictalurus punctatus) containing salmonid growth hormone genes can grow 33% faster than normal channel catfish under aquaculture conditions. However, before transgenic catfish are released and utilized by the private sector, their genetic impact on the natural environment must be examined. Predator avoidance is one of the major fitness traits determining potential environmental risk. To determine the predator avoidance ability and growth performance of transgenic catfish in a natural habitat, various densities of transgenic and nontransgenic channel catfish were communally stocked in 0.04-ha earthen ponds without supplemental feeding. Largemouth bass (Micropterus salmoides) and green sunfish (Lepomis cyanellus) were stocked as predators. Nontransgenic fry had better predator avoidance than transgenic channel catfish when data were pooled (p <.01). When data were not pooled, nontransgenic catfish had better predator avoidance in six trials and transgenic individuals had better predator avoidance in four trials. There was no difference in predator avoidance in three trials. Overall predator avoidance was also better for nontransgenic individuals (p <.01) when the fish were evaluated as 3.5-g fingerlings, more clearly than as fry, as transgenic individuals were more vulnerable in 3 of 4 trials at this life stage. There was no significant difference in growth performance between transgenic and nontransgenic channel catfish in ponds without supplemental feeding. These findings indicate that transgenic channel catfish could be used for commercial aquaculture without affecting the natural environment. Although transgenic channel catfish may be released to nature by accident, any ecological effect would be unlikely because the increased susceptibility of transgenic channel catfish to predators would most likely decrease or eliminate the transgenic genotype.
ABSTRACT
: Expressed sequence tag (EST) markers are important for gene mapping and for marker-assisted selection (MAS). To develop EST markers for use in catfish gene mapping, 100 randomly picked complementary DNAs from the channel catfish (Ictalurus punctatus) pituitary library were sequenced. The EST sequences were used to design primers to amplify channel catfish and blue catfish (I. furcatus) genomic DNAs. Polymerase chain reaction products of the ESTs were analyzed to determine length polymorphism between the channel catfish and blue catfish. Eleven polymorphic EST markers were identified. Five of the 11 EST markers were from known genes and the other six were from unidentified ESTs. Seven ESTs were found to be associated with microsatellite sequences. Analysis of channel catfish gene sequences indicated highly biased codon usage, with 16 codons being preferably used. These codons were more preferably used in highly expressed ribosomal protein genes and in highly expressed pituitary hormone genes. G/C-rich codons are less used in channel catfish than those in other vertebrates suggesting AT-richness of the channel catfish genome.
