Fish farms and the sustainable food fight

Overfishing is threatening more than 90 species in Europe with extinction. While fish farms were once tipped to help offset the effect of plummeting stocks, it turned out they can actually make matters worse.

Aquaculture, or fish farms, will soon surpass wild fisheries as the main source of seafood. In theory, they could help relieve the pressure on wild stocks, except that the food given to fish in farms, called aquafeed, is often dependent on smaller wild species, like anchovies and sardines, which, when overfished, sends shockwaves up the food chain.

'Wild fish stocks used to be the basis of the raw material (of aquafeeds) and have gradually been replaced by plant ingredients. This effort needs to be continued so wild stocks are managed in a sustainable way and they are not exploited as aquaculture continues to increase,' said Ivar Rønnestad, Professor in Environmental Physiology at the University of Bergen, Norway.

But staying out of our oceans might not be an option as it's difficult to make fish without fish.

'Fish need protein to grow and the challenge with plant protein and other alternative ingredients is that some of them have anti-nutrients while the nutrient composition and quality is not fully sufficient for growth,' said Prof. Rønnestad, who is also the coordinator of WISEFEED, an EU-funded project looking to improve the sustainability of aquafeeds.

To solve this, the project, which started this year, will examine the metabolism of farmed fish and develop an aquafeed that combines plant and marine ingredients in order to get the most efficient growth while lowering aquaculture's dependency on wild fish.

'Sustainability will be balanced between increasing demand and limited resources,' said Prof. Rønnestad.

To find the most sustainable feed for a variety of species they are carrying out dietary experiments in Portugal, Spain and Vietnam.

Finding Nemo-todes

Farmed fish go through a two-tier system before reaching the supermarket: the nursery stage, where juveniles are hatched, and the farm where they go to fatten up.

'A lot of fish need food that is alive and moves, that is the trigger to feed and it's the same for freshly hatched fish and crustaceans,' said Matthias Nölting, coordinator of NEMAQUA, an EU-funded project developing a sustainable solution to supplement or replace artemia, the most important current feed for hatcheries.

Artemia are tiny crustaceans found in natural salt lakes, mainly in the US where 70-80 % of the production exists. They have a survival mechanism where they transform into dormant eggs, known as cysts, which can then be easily stored.

When a hatchery needs to feed their baby fish they expose the cysts to water so they can come back to life and be eaten.

'According to statistics, the world sits at roughly 4 000-4 500 tonnes of quality product each year,' said Nölting. 'As fish farming grows at large rates, this is in danger of becoming a bottleneck.'

Overfishing artemia one year has a direct negative impact for the following season, which has forced the authorities and fisheries to run a harsh regime to prevent exploitation. Expanding production to other locations is limited as there are very few other natural salt lakes that offer suitable conditions.

Finding an alternative to artemia would therefore allow aquaculture to address another unsustainable link in its food chain.

'It is observed in the wild that some fish are also feeding on nematodes,' said Nölting, whose company e-nema uses a large silo to grow these micro-worms, the most abundant non-vertebra animal on earth, to eat pests on fruit farms.

NEMAQUA has proven the economical, biological and technical viability of a selected strain of nematodes in feeding juvenile shrimp. They hope to start commercialisation in 2017 while trials for fish will begin in the next two years.

Fish poo

When farmed fish gorge too much on land-based ingredients they can excrete high levels of nitrogen. This leads to an excess of nutrients in the surrounding water that can reduce oxygen, cause algae growth, and kill off other species.

But reusing this waste could actually prove to be a sustainable business opportunity.

'Aquaponic systems have two complementary crops, fish and plants, therefore generating an extra income that helps maximise the economical profitability of the facility,' said Professor Adrian Turek Rahoveanu from the University of Agricultural Sciences and Veterinary Sciences of Bucharest, in Romania.

Prof. Turek Rahoveanu is the coordinator of ECOFISH, an EU-funded project looking to convert conventional aquaculture farms into aquaponic ones. The project tested an aquaponics fish farm system at the University of Galati, also in Romania.

This included using farmed sturgeons and rainbow trout to grow lettuce and spinach. However, they found a big technical and financial challenge in transforming fish farms into aquaponic systems, due to the complexity of the systems.

But, according to a survey carried out by ECOFISH, aquaponics systems could still appeal to fish farm owners and supermarkets.

'High productivity and phytoremediation (using plants to clean water) capacity of several combinations of fish-plant species were found to have positive results,' said Prof. Turek Rahoveanu.

'It is essential for the feed administered to fish to have organic compounds which are then always found in wastewater,' said Prof. Turek Rahoveanu. 'This can be a source of income.'

From its inputs to its outputs, aquafeed creates sustainability issues during the entire lifespan of farmed fish.

With fewer marine species in aquafeed, reduced pollution, and potential for more fish farms, aquaculture's weak spots can be strengthened, alleviating stress on wild fisheries.