Better breeding could counter cod brood difficulties

The Fish Site
by The Fish Site
29 August 2007, at 1:00am

NORWAY - Preliminary indications from a three year international research project into cod farming have shown that commercial brooding and production efficiency could be improved by selection techniques and DNA typing, writes Jane Jordan, FishSite Editor.

Dr Oddvar Ottersen says Cod North has produced very intersting results that now warrant further investigation.

The transitional project, North Cod, has found that spawning behaviour is a major limiting factor in breeding efficiency. The species are notoriously difficult to brood -a principal reason being the reluctance of a significant number of mature adults to reproduce.

"Certain adults, within a population, will breed, but for some reason others won't. Also, only certain females produce eggs and not all males will contribute," explained Dr Oddvar Ottersen, North Cod project leader based at Bodø University in Norway. He says the behaviour could be a natural response to food resources and/or population density.

However, this is a significant problem for hatcheries, which if resolved could offer massive benefits to productivity and commercial efficiency.

"Being able to identify which parents are likely to breed means that resources could be optimised and so hatchery efficiency improved," said Dr Ottersen.

Part of the project also explored the potential of cryo-preservation (freezing) of cod sperm. The trials proved positive with 80 per cent fertilisation rates and a similar success rate in hatched larvae survival. The technique could also be a viable means of overcoming the male fish's reluctance to breeding.

North Cod has also identified that egg quality deteriorates as the spawning season, from February to April, progresses. Peak productivity is mid-term, when spawning rate and the number of viable eggs produced increases. A better understanding of this trait, and the knowledge of which parents are prolific and productive, could have huge commercial significance with particular advantages for hatchery management and productivity.

Genetic ID

The project has also explored DNA typing and genetic marking and infuture selection programmes should help to improve the hybrid vigour and breed potential of farmed cod genotypes. Dr Ottersen says that reproductive traits and growth performance are a priority for breeders and fish farmers. However, this area of research is still at the early stages.

Much of the technology used to produce farmed salmon can be applied to cod - once fish reach the cage stage. And it's a very viable enterprise. However, raising brood stock and fry is extremely difficult. The hatchlings and developing fry are extremely small, compared with salmon. Hatchlings rely on the yoke sack for a longer period post-hatching and the fry also require live food.

Rearing young stock is complicated, they need a specific nutritional regime and careful management as the species are not as robust as salmon. However, once they are four months of age, cod will perform well in offshore cages under commercial conditions, reaching a mature saleable weight in about two years.

Dr Ottersen believes that with genetic selection and improvements to nutritional technology the challenges faced during the hatchery/rearing phase will be resolved. The findings of this research project - although preliminary - have established key areas for further investigation.

"Feedback from the project has been excellent and all the partners involved are eager to progress the research. The prospects are exciting and it warrants further investigations," said Dr Ottersen.

North Cod's activities are industry-led with the emphasis firmly on commercial development. The findings of this research now need further investigation to establish how it can be applied commercially and to establish true economic advantages.

Any improvements in cod farming will be valuable to both aquaculture and marine fishing. The market for farmed cod is expanding and prices are favourable. Also, the commercial development of this sector will take pressure of depleting ocean fish stocks.

The project was financed by the EU regional periphery programme. Four countries contributed - Norway, GB, Iceland and Russia. The primary objective was to establish a more sustainable means of producing cod fry and to promote successful farmed production of the species.

The initial outcome of North Cod's research has been the production of hatchery production manual. It contains details on recommended management practice and will be available on the North Cod website during the autumn.