Aquaculture is growing rapidly around the world and is playing an increasingly important role in ensuring food security. Iceland is the largest producer of char in the world, but char has a great need for protein, which has mostly been met by feed that is rich in fishmeal. Fishmeal, on the other hand, is an expensive source of protein, so feed costs in charr farming are around 50% of production costs, in addition to which fishmeal is a limited resource. It is therefore important to look for new protein sources for char producers. One such option is to use soybean meal, which has been used successfully in salmon farming. However, there are studies that suggest that soybean meal may have a negative effect on the growth, intestinal flora and general well-being of salmonids.
This report discusses the main results of the AVS project "Development of new charr feed", the aim of which was to reduce feed costs and increase sustainability in charr farming by replacing fishmeal with soybean meal in feed. The project also sought to gain an understanding of the effects of different "treatment" soybean meal on the growth, intestinal flora and welfare of char.
Four different types of feed were studied, ie. conventional feed with fishmeal (FM), with untreated soybean meal (US), with enzyme-treated soybean meal (ES), and with untreated soybean meal with added beneficial bacteria (USP). The survival, growth, behavior and intestinal flora of the char fed for 10 weeks on the aforementioned four types of feed were then compared. The char that was tested was a small fish at the stage where there is a lot of growth and the intestinal flora is being shaped; and therefore the effect of the feed is particularly important.
The main results of the project were that feed containing Hypro soybean meal with added FOS beneficial bacteria significantly reduced growth, compared to the other types of feed. The enzyme-treated soybean meal, which contained degraded NSPs that act as beneficial bacteria, as well as the untreated soybean meal with added beneficial bacteria, contributed to a more diverse intestinal flora and increased levels of lactic acid bacteria (LABs) that have been linked to disease and immune resistance, . The results also showed that the fish's behavior towards the untreated soybean meal was significantly different from that of the other feeds, in that they showed less interest in the feed.
The results indicate that the addition of beneficial bacteria at this stage of growth promotes positive changes in the intestinal flora, and can therefore lead to increased tolerance to stress and disease later in life. However, this seems to be detrimental to fish growth. Further research is therefore needed to determine whether the growth will pay off in the later stages of charr growth and whether survival and other positive traits will increase. FOS benign bacteria may not be suitable for fish at such an early stage of development, but it seems that FOS affects metabolism and intestinal needs and the immune system. But further research is needed to draw further conclusions. The enzyme-treated soybean meal did not have the same negative effect on growth, but the variability was greater. LABs in the intestinal flora indicate that the treatment promotes endangered health and resistance to infections, without affecting growth. The results suggest that enzyme treatment of soybean meal in feed contributes to improved health and survival of char. It is important that future research examines the results of this project and compares it with the condition of intestinal tissues. It is also important to further investigate how metabolism, behavior and intestinal flora interact with different feeding in previous life stages, as well as what the effects are on long-term growth and well-being.
Skýrslan er lokuð / This report is closed
Aquaculture is globally growing in importance as part of the solution for future food security. In Iceland one of the most important farmed species is the salmonid, Arctic Charr, and Iceland is the world's leading producers of this cold-water, carnivorous species. Arctic Charr has a high dietary protein requirement which is traditionally provided by diets high in fish meal protein. This drives feed costs that are 50% of the total production costs and puts pressure on wild capture fisheries from which fish meal species are sourced. To facilitate the further expansion of Arctic charr aquaculture it is necessary to find less expensive and more environmentally sustainable feed ingredients. One potential alternative that is widely used in Atlantic Salmon aquaculture is soybean meal, however increasing evidence suggests that for some salmonids, untreated soybean meal can have negative consequences for growth, good health and welfare.
The overall aim of this study was to decrease Arctic Charr feed costs and improve the long-term sustainability of salmonid aquaculture in Iceland by replacing fish meal with untreated and treated soybean meal. This study also aimed to understand the wider consequences of untreated and treated soybean meal on the growth, gut health and welfare of Arctic Charr.
Four different diets were assessed, a fish meal control (FM), an untreated soybean meal (US), an enzyme pre-treated soybean meal (ES) and an untreated soybean meal with an added prebiotic (USP). The survival, growth performance, gut microbiome assembly, and behavior were of juvenile Arctic Charr fed each of these diets during a 10-week feeding trial were compared. The juvenile life stage was selected since it is a period of crucial developmental, when growth rates a very rapid, and the gut microbiome is colonizing, so impact of differing diets can be obtained quickly.
The key findings of this report were that the addition of FOS prebiotic to untreated Hypro soybean meal feed treatment significantly reduced growth compared to the fish meal control when all other feed treatments including the enzyme treated soybean meal performed significantly the same as the fish meal control. The enzyme treatment of soybean meal which aimed to have a secondary benefit of the broken down NSPs acting as prebiotics, as well as the untreated soybean meal with prebiotic had higher gut microbiome diversity as well as a greater presence of Lactic Acid Bacteria (LABs) which are both associated with positive benefits such as more immune robustness and resilience to disease and infection as well as benefits for nutritional uptake and growth. There was also a notable difference in behavior where the fish fed the untreated soybean meal with added prebiotic were both shyer and less active than the fish fed any other feed treatment, indicating that they were more reactive individuals.
When the results of these different tests are viewed together this suggests that the addition of pure prebiotics at such an early developmental stage does promote beneficial changes to the gut microbiome which suggests that the fish will be more resilient to stress and disease later in life and may receive other benefits of prebiotic addition too, however at this early stage the combination with low growth performance suggests that the immune system and gut development may be stimulated but at the cost of energy being drawn away from growth. Salmonids given FOS should be followed from early development through to harvest to see if growth can be compensated and if survival or performance is in fact improved. Otherwise these results may indicate that FOS may not be suitable to apply to diets during such early stages of development, when growth curves are steep naturally. The observation that these fish were also had more reactive coping strategies suggests that the prebiotic application may also effect metabolic rate which could be linked to the stimulation of the gut and immune system, but further experimentation will be needed to elucidate this and also to investigate the consequence of this altered behavior, which could potentially reduce the welfare of an intensively farmed fish. On the other hand, the enzymatic treatment of soybean meal did not show the same negative impact to early growth performance but did influence a higher diversity and LABs presence in the gut microbiome suggesting this method of threatening soybean meal may bring benefits to health and resilience without as much trade-off. These enzyme-soy treated fish groups were also slightly more reactive than the control treatments, but the impact was not as pre-announced as for the prebiotic added treatment. Overall the results suggest that the best potential benefit to long term health and survival of charr when soybean meal is pre-treated with enzymes when used in the diet.
It will be extremely important in the future to combine these results with gut histology data to clarify the impact of differing treatments to internal gut morphology and health. It will also be important to further study how metabolism, behavior and the gut microbiome interact with dietary treatments at this early development stage and what the long-term consequences for production and welfare will be.