Research to make aquaculture more sustainable

by Thomas Jensen
Aquaculture cages italy

Finding ways to reduce the environmental impact of fish farming

This article was featured in Eurofish Magazine 2 2023.

Finding carbon neutral ingredients for fish feeds and experimenting with multitrophic aquaculture are among the ways researchers are trying to make Italian aquaculture more sustainable.

As sustainability gains increasingly in importance it also affects companies in the aquaculture sector which, as a consequence, are working to make their operations more environmentally friendly. Aquaculture feeds were responsible for 60-70% of the carbon footprint of the aquaculture value chain when fishmeal and fish oil were the main ingredients in fish feed. And fish farming operations affect the natural environment due to their biological and chemical impacts.

Moving forward on many fronts

Today, however, the use of fishmeal and fish oil in fish feeds is very efficient. From the main constituent of a feed, they are now used in much smaller volumes, as an additive to increase palatability or to add certain amino acids to the feed. Yet advances in feed technology enable a feed conversion ratio that gives about 5 kg of fish for each kilo of feed, says Prof. Alessio Bonaldo from the University of Bologna. Antibiotic utilisation, a source of chemical impacts, is decreasing year by year and already many farms are certified antibiotic-free. In addition, genetic selection can select strains that are more resistant to diseases and pathogens—which also reduces antibiotics use. Multitrophic aquaculture combines the production of fish with that of seaweed or molluscs which absorb the nutrients released by the fish farming. This makes the fish production more sustainable and at the same time creates an additional product (seaweed or molluscs) for sale.

Another technology that reduces water and energy consumption is recirculated aquaculture systems. These are used already in hatcheries for the production of juvenile fish, but as the climate gets hotter and drier farmers are becoming more interested in these systems for the production of market-sized fish. The aquaculture industry in general is very interested in reducing its impact on the environment because, as Prof. Alessio Bonaldi says, the connection between farmed fish and the natural environment is very close. Unlike terrestrial farmed animals which are housed in buildings separated from the environment fish are farmed in the sea where there is no such separation. Fish farmers and feed manufacturers therefore try to reduce their products’ impact on the marine environment as far as possible.


Using ingredients grown from by-products

One way of doing this is to find ways of substituting fishmeal and fish oil with other ingredients. Prof. Bonaldo is involved in three projects. NewTechAqua seeks to use by-products and coproducts from fisheries and aquaculture such as trimmings and other leftovers from slaughtering and ­processing operations. These ingredients were enriched with algae to balance the omega-3 content in the diets. In another project, NEXTGEN Proteins, the researchers tested insect meal, algae meal and single cell protein from yeast. One of the objectives of the project was to replace the fishmeal and soya meal content of fish feeds. In SUSTAINFEED the purpose was to test plant ingredients, coproducts or by-products from other value chains, that do not compete with human consumption. In all three projects the feed products were tested for performance, fish welfare (especially gut health), and fillet quality. The results suggested it was possible to decrease fishmeal content and the fraction of other more unsustainable substances with the new ingrdients. The results also showed that seabream in particular is able to convert low quality proteins into good animal proteins without detrimental effects on welfare or fillet quality. The new ingredients were circular in the sense they were produced from coproducts or by-products coming from another value chain. For example, the yeast in the NEXTGEN Protein project were fed with waste from the forestry industry. This circularity adds value in terms of carbon footprint and nutrient valorisation.

Entire value chain must be considered when testing new aquaculture species

Apart from the environmental goals the purpose is also to try and maintain feed costs at a stable level for the sake of the fish farmers who face price increases for all their inputs. Feed is the most significant cost for them accounting for up to 60% of the total. Any increase in feed prices has thus a major impact on their costs. One way to reduce production costs that is also being considered is by cultivating omnivorous or herbivorous species. The challenge is consumer acceptance. More generally it is important to look at the entire value chain from production to processing to marketing when considering new species. In Italy new marine finfish species under trial include dusky grouper, amberjack, shi drum and mullet, says Prof. Clara Boglione from the University of Rome Tor Vergata. Mullet is grown mostly in the lagoons of Venezia and Sardinia, but it is scattered and the volumes are small. Greater amberjack and Mediterranean tuna are cultivated in Sicily but with irregular production. So, essentially, fish aquaculture in Italy is focused on seabass, seabream and shi drum in the sea and trout and sturgeon in fresh water. However, experiments are being conducted in the framework of community-like aquaculture, where sea cucumbers and sea urchins are reared in combination with marine species. This is a form of multitrophic aquaculture, where the sea cucumbers and sea urchins are grown beneath the fish cages or mussel longlines to mitigate the impact of the nutrients released by the reared organisms. The two species are valuable products themselves and represent an additional income stream.

Growing juveniles in low density results in higher quality

Prof. Boglione specialises in analysing the impact of rearing conditions on the fish skeleton. In the past, she has described how semi-intensive rearing conditions (characterized by large tanks coupled with low stocking densities) are able to produce juveniles of gilthead seabream, European seabass and dusky grouper with body shape and pigmentation similar to that of wild fish and with fewer deformities than are found among juveniles raised in intensive rearing conditions. In the framework of the BioMedAqu project, she collaborates with the University of Las Palmas to analyse the effects of dietary vitamin D3 levels and dietary supplementation of copper on gilthead seabream skeleton. In the same project, the collaboration with the University of Las Palmas, University of Algarve, IPMA (Instituto Português do Mar e da Atmosfera) and API (Associazione Piscicoltori Italiani) demonstrates better survival and growth rates, and lower incidences of some skeletal anomalies when gilthead seabream larvae and pre-ongrowing juveniles are reared in low-density conditions. The quality when you rear at low density is much better, she says, but convincing farmers that it is better to breed fewer high quality fish rather than many of lower quality is not an easy task. Some farmers do rear juveniles at low density and then sell them at a higher price. Most, however, rely on the cheaper intensively reared juveniles. This is partly because the rapid market expansion in the 1980s with the subsequent oversupply from Turkey and Greece has lowered the market value of gilthead seabream over the last two decades.

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