“Our overall finding is that farmed fish fed low levels of marine ingredients – fishmeal and fish oil at inclusion rates of 5% and 3% respectively of complete feeding stuffs – had excellent performance. Their fatty acid requirements were met at that ratio.
“This data gives feed companies quite a latitude in terms of aqua feed formulation,” said Dr Sadasivam Kaushik, honorary director of research, INRA, and coordinator of the Advanced Research Initiatives for Nutrition and Aquaculture (ARRAINA), a project charged with evaluation of the effects of plant based diets on the full life cycle of fish farmed in Europe, namely Atlantic salmon, rainbow trout, common carp, sea bass and gilthead sea bream.
And he said the team has made significant progress on assessing the impact of high dietary levels of plant proteins and vegetable oils on different metabolic pathways and processes.
The ARRAINA researchers, who are due to submit project conclusions to the EU Commission in February, also examined whether nutritional intervention or stimulus during a critical period of development in three fish species – rainbow trout, Atlantic salmon and European sea bass - can result in a persistent effect, an “imprint”, lasting into adulthood and, in that way, aid more optimal use of marine ingredients.
“We evaluated whether feeding a diet rich in plant proteins in the early life stage, followed by a diet including conventional feedstuffs, and then a challenged one comprising plant proteins and low quantities of fish oil and fishmeal would trigger the bioconversion capacity of certain species - that is their ability to elongate and desaturate plant based alpha-linolenic acid (ALA) into the essential fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
“We got some really interesting results, some papers have already been published, others will be released in around six months to a year’s time,” Kaushik told FeedNavigator.
That nutritional programing concept is based on epigenetics – the processes that induce heritable changes in gene expression potential without altering the gene. “We looked at enzyme activity and used tools to measure gene expression to determine desaturation,” he added.
Tailoring fatty acid use
Tailoring fatty acid use to finishing feeds, adding fish oil in salmon diets a few weeks before harvesting, for example, is also an efficient use of essential fatty acids, as retention of fat is higher then, said Kaushik. “But how widely this approach is practiced in EU aquaculture production needs to be investigated further,” he added.
The ARRAINA researchers have also just released a booklet looking at the “reliable” biomarkers that are available to assess the nutritionally mediated effects of plant based diets on growth performance, metabolic homeostasis, stress responsiveness and health condition of EU fish species from early life stages to completion of production cycle and maturation.
The team said of particular value are predictive and non-invasive biomarkers available at a relatively low cost, but the combination of conventional and omics approaches is emerging as a user-friendly option.
Biomarkers rated as beneficial are those that can forecast “the onset of metabolic disturbance or predict the capacity of the animal to cope with dietary, environmental and age-related stresses.
“It is difficult to generalize due to differences in growth performance, nutrient requirements and life cycle of the five key commercial species of European aquaculture, although significant advances have been made in the development of interactive tools, including new genomic resources, such as transcriptomic gilthead sea bream and European sea bass databases,” noted the publication.
The initiative has also resulted in a “user friendly” database of biomarkers in fish nutrition. The tool, said the team, is designed for single or combined searches of biomarkers that provide information on nutrient requirements or changes related to specific biological or metabolic processes.
The biomarker booklet followed the release of ARRAINA publication in September last year providing an update on the nutritional requirements for the main EU aquaculture species.
Vitamin and mineral levels in fish feed
The ARRAINA project had a strong focus on identifying minerals, vitamins, amino acids, lipid components that need to be added to feeds containing high levels of plant products to avoid reduced performance and health status in farmed fish.
Normally, micronutrients are added as a premix to fish feed, based on existing recommendations such as those by US National Research Council (NRC, 2011). One of the aims of ARRAINA was to see whether those NRC levels should be amended given current inclusion level of plant based ingredients in fish feed.
“Based on growth, nutrient retention and metabolic biomarkers used in studies undertaken as part of ARRAINA, NRC (2011) recommendations existing for rainbow trout (O. mykiss) for folate, thiamine and biotin were identified to be valid also for Atlantic salmon (S. salar), while pantothenic acid, niacin, cobalamin and pyridoxine needed to be increased above the NRC (2011) recommendations,” noted one section summarizing research outcomes related to vitamin B levels in plant based feeds.
But the researchers concluded no new recommendations can be made yet on the best level of vitamin D from the ARRAINA project.
Studies undertaken as part of ARRAINA confirmed that there is a linear relationship between dietary and whole body selenium concentrations in Atlantic salmon. However, the team noted the difficulty around finding good biomarkers for fulfilment of the selenium requirement in fish, and concluded there isn’t sufficient data to recommend changes in minimum dietary concentrations from NRC (2011) of 0.15 mg/kg for salmon, 0.35 mg/kg more generally for fish.
In other ARRAINA studies, again on Atlantic salmon, the scientists found there was a clear difference in zinc requirement of freshwater and seawater fish. Whilst the freshwater fish requirement was in line with the assumed requirement, the seawater fish had a much higher requisite in terms of zinc levels.
And they noted the manganese levels in the plant ingredients were sufficient to cover that requirement in Atlantic salmon.