Aquaculture  - Biotechnology topics

For millennia, farmers have assisted natural selection to build herds that thrive in farm environments and have had remarkable success. Over the last half century alone, the agriculture industry has doubled the milk produced by a single cow, doubled (or tripled) the number of eggs chickens lay and cut to about six weeks the time to bring a chicken to market size.

In the aquaculture industry, too, good breeding is essential to success – but selecting top breeding Dungeness crabs or haddock poses a unique set of challenges that are not faced when breeding and crossing top performing land farm animals. How can shellfish hatcheries, for example, select the best potential breeders from populations that normally hide away under the sea… or sand!?

Hatcheries in British Columbia are beginning to look at establishing broodstocks of Dungeness crabs, red sea urchins and geoduck clams. Because they can only, practically, handle small numbers of broodstock individuals, inbreeding will rapidly occur if there is no protection of genetic diversity. Such protection hinges on being able to distinguish one top-performing family line from another. An added complicating factor is that offspring of individual matings are rarely held separately from each other – so how can breeders accurately follow or track their breeding lines?

Good Breeding - "To the Manner Born"

Scientists at Fisheries and Oceans Canada (DFO) are working with researchers in the aquaculture industry to develop state-of-the art tools to help solve these problems. For example, Dungeness crab breeders often have difficulty getting reliable results from tests for genetic variability in wild stocks from which their broodstock populations are founded. Research is, therefore, focusing on development of rapid and inexpensive DNA probes, capable of screening thousands of individual shellfish. This information is used to build a ‘genetic portrait’ (database or library of genetic information) of the genetic diversity in as wide a range of wild populations as possible.

With this information, DFO scientists can identify areas of DNA that vary from one population to another, as well as between family lines. These gene code variations can then be isolated and copied to produce genetic ‘markers’ for that population or family. Once these markers are made, it is a relatively simple matter to develop probes for them. This allows the scientists to identify individuals, which show the widest genetic diversity between each other for selection for breeding programs. By selecting individuals with the maximum genetic diversity possible, scientists give industry the optimum animals they need to begin a selective breeding program without risking immediate inbreeding.

Identity crisis!

The same innovative technology is helping breeding programs track their best performers over several generations. For example, it takes two to three years to condition Atlantic halibut broodstock prior to producing good quality eggs. If the young are reared together, it is difficult to keep track of the most successful crosses, and significant inbreeding can result. Scientists studying halibut broodstock, selected by traditional methods, such as physical characteristics, growth rates, etc., found that many were siblings or half-sibs.

Similar problems confront haddock breeders, but traditional solutions – such as physically separating breeding lines – are not practical in most of today’s fish culture environments. Like the halibut, Canada’s cultured haddock have been reared together, so individual pedigrees are unknown.

Studying fish genealogy – Getting to the Pedigree…

To solve the problem of identifying the pedigree of individual fish, DFO scientists are extracting DNA using tiny clips of fin tissue or blood samples, from potential halibut broodstock. They look for highly variable regions of the genome and select sections that represent a genetic ‘fingerprint’ for each individual. Since these differ from all other possible parents, this allows the scientists to track the pedigree of their offspring.

By knowing this pedigree, breeders can avoid inbreeding and, at the same time, determine which crosses were most successful. The technology removes the need to separate offspring into family groups to monitor performance, since genetic markers can track individuals through successive generations.

Not only is group rearing more economical, but it is also good science. All juveniles are exposed to the same holding conditions, thus, any difference in performance are more likely due to genetics – rather than environmental variables. This makes selection of ‘top performers’ more reliable.

Natural Tags you can see with the Naked Eye - Breeding in differences:

Genetic technology also makes it possible for scientists to include unique or unusual individuals in the breeding stock – such as shellfish with a rare colouration pattern. If the gene for such a colour trait is rare (i.e., the gene is usually suppressed in matings with ‘normal’ colouration parents), selection of such individuals for hatchery broodstock ups the chances of producing greater numbers of the rare colour. As long as the colour gene is not linked to an undesirable feature (e.g., slow growth), this provides a useful natural tag to identify cultured shellfish in the marketplace or open-water beds.

Best of all, the DNA tools promise to help breeders identify the genetic traits that most influence survival and growth of hardy (and sustainable) breeding populations. For example, is it egg-laying rates that count, or larval survival, that makes the biggest difference to population growth? Which genetic qualities promote vigorous health and growth? Partnering biotechnology and aquaculture, provides us with the opportunity to find answers to questions that have eluded scientific definition for generations.