Fishing Continues to Evolve

Aquaculture, or fish farming, has been around worldwide for thousands of years: tilapia were farmed in Egypt 4000 years ago; the Chinese were tending carp in fish ponds 2,500 ago; the Aztecs used a chinampas system rearing carp in irrigation ditches; and a rotational cropping system was practised in Europe by the 14th century – three years of agricultural crops were rotated with three years of fish crops.

The fish used in these ancient systems were all herbivores, i.e. plant eaters, according to an article in Peace Arch News.

Today’s modern practice in the northern hemisphere is based on carnivorous species – salmon, shrimp, tuna – so other fish species lower on the food chain must be caught and processed into pelletized feeds for them. Although this inefficient technique is being improved, the result is still a net drain on fish populations. Ten years ago, 1.9kg of wild fish were required to yield 1.0kg of farmed fish for sale; now the ratio is down to 1.3 to 1.0 but that is still negative.

With Norway leading, moves are afoot to make better use of slaughterhouse wastes, by-catch fish, modified pellets which sink only slowly and by selective breeding to achieve a positive or at least neutral ratio.

This negative ratio of food input to harvested fish is just one of the ‘strikes’ against fish farming, according to the Peace News Arch article. The question of concentration and sea lice infestation is currently debated hotly. Pollution from unused feed pellets and from excrement is being addressed ecologically with indications of real improvement in tests in New Brunswick’s Bay of Fundy. Integrated Multitrophic Aquaculture requires large salmon cages with units holding blue mussels immediately downstream to filter the wastes flowing from the salmon cages. Beyond the mussels are rafts of kelp, which take up nutrients from the run-off waste stream.