How Enzymes Can Improve Aquafeed Utilisation

Global seafood production - including all species of fish, crustaceans and molluscs - is estimated at 179 million tonnes. According to the latest FAO statistics, aquaculture's total contribution is around 114.5 million tonnes in live weight, of which aquatic animals represented 82.1 million tonnes (FAO, 2020; Figure 1).

Ensuring adequate food and nutrition security to a globally growing population is still a daunting challenge and aquaculture has a prominent role to play in world food security. Globally, food fish consumption has increased annually by around 3.1%, which is higher than all other animal proteins (such as meat, dairy and milk) which have increased by 2.1% annually. On average, production of farmed aquatic animals has grown by 5.3% annually (FAO, 2020). 

Figure 1. World aquaculture and capture fisheries production

Alongside aquaculture growth, the aquafeed markets have followed the same fast-growing trend. Recently, aquaculture feed production was estimated to be around 57 million tonnes (FAO, 2020). The split of the main species is dominated by caprs, with approximately 28%, tilapia 18%, marine shrimp 14.6%, catfish 11.2%, marine fish 8.1%, salmon 6.9%, freshwater crustaceans 4.6%, other freshwater fish 3.6%, trout 2.1% and others 2.9% (Tacon, 2018; Figure 2). 

Holding a world-leading position in the feed enzymes market, Huvepharma brings highly efficacious enzymes which are registered for use in aquaculture in some key countries. 

Figure 2. Total aquafeed estimate per species (%)

Hostazym® X: boosting feed digestibility

Hostazym® X is a highly efficient fibre-degrading enzymatic complex which increases nutrient digestibility, resulting in better growth performance and a healthier gut environment. Hostazym® X is the only fibre degrading enzyme approved by the European Commission to be used in feed for carp species. 

Aquaculture trials are often completed in environmental conditions that allow the full potential of a feed additive to be demonstrated. To challenge Hostazym® X, a trial was conducted at an outdoor facility at the University of Poznan, Poland. This trial allowed Hostazym® X to be tested under adverse conditions. In contrast to previous research trials, water temperature fluctuated from 13.5 to 24.7^oC and dissolved oxygen ranged from 2.0 - 5.1mg/l. Oxygen has a big impact on feed conversion ratio in fish and, when faced with a deficiency, the growth rate and health status of the fish decrease. 

The trial was set using three different concentrations of Hostazym® X: 1,050, 1,500 and 3,000 EPU/kg feed against a control feed. Twelve 40m² ponds were each stocked with 20 x 375g fish and fed for 90 days. No mortalities were observed during the trial. 

Hostazym® X performance for all three levels of inclusion was better than the control. The results are presented in Table 1 and Figure 3 and clearly show that: 

• Body weight significantly increased compared to the control
• Adjusted FCR decreased compared to the control
• Farmers who use Hostazym® X get a better return on their investment

Table 1. Key growth parameters. *Adjusted FCR to control final body weight. Different superscripts represent statistical difference at p ≤ 0.05.

Figure 3. Cost saving per 1,000 metric tonnes of fish produced versus control

OptiPhos®: reducing phosphorus waste

Phosphorus is essential for all life and is required for optimum growth, feed efficiency and bone development in fish. While an essential nutrient in aquaculture feed, it also has an environmental impact and is responsible for eutrophication in many lakes and rivers (Serwata, 2020). 

The goal of sustainable aquaculture is still far from being achieved, with fish retaining only ~40% of the phosphorus they consume in modern commercial fish feeds. Reduction of phosphorus levels in feed without impacting growth, feed efficiency and health is key to the development of low pollution diets. This is currently being achieved by the use of low-ash fishmeal or readily available phosphorus supplementation. However, there are other more cost-effective strategies. Phytase enzymes efficiently release otherwise unavailable phosphorus from the increasing inclusion of vegetable ingredients have a very important role to play. 

Large amounts of organic phosphorus bound in phytic acid are present in modern day salmon and trout diets but these rae poorly utilised. This represents an opportunity to utilise OptiPhos®, a globally recognised phytase enzyme to help reduce the environmental impact of the salmonid industry (Serwata, 2020). 

Fish feed contains high levels of vegetable protein sources (used as a replacement for fish meal), resulting in high levels of phytate in the feed. Phytase hydrolyses the phytate (phytic acid) and releases bound phosphorus, allowing significant financial savings by reducing the amount of inorganic phosphorus used. Additionally, the excretion of phosphorus into the environment is also significantly reduced. 

Global salmon and trout production in 2020 stands at circa 3.2 million tonnes. This production is dominated by Atlantic salmon and over 50 percent of this is produced in Norway, while the other main players are in Chile, the UK, the Faroe Islands, Iceland, Ireland and Canada. Salmonid production, like that of most farmed animal species, does not have a great track record in terms of environmental impact, though huge efforts have been made by the industry to clean up its image.

The salmon industry in Norway produces ~1.24 million tonnes of salmon and ~1.65 million tonnes of salmon feed. This industry is also the third largest importer of inorganic phosphorus (16,500 tonnes), even surpassing domestic phosphorus fertiliser usage. 

Trials conducted on rainbow trout (Onchorhynchus mykiss) and Atlantic salmon (Salmo salar) demonstrated that phosphorus levels in the feed can be reduced significantly (2.5 - 3.5 g/kg) and that in some cases, added inorganic phosphorus could be eliminated completely. 

There are also financial benefits in implementing an OptiPhos® strategy. Increasing digestible energy (DE) levels in salmonid feeds has a significant impact on space in formulations. Competition for space can add significantly to formulation costs, so any opportunity to optimise space utilisation can provide a significant cost benefit. 

OptiPhos®, by reducing the necessity for phosphorus supplementation, can offer formulation cost savings of up to €15 per metric tonne, a win for both economic and environmental sustainability. This excludes any opportunity the farmer may have to increase production volumes and make better use of production biomass consents, which could be significant.

Figures 4 and 5 show the positive impact of Optiphos® on phosphorus retention and excretion in different trials with Atlantic salmon and rainbow trout. 

Figure 4. Atlantic salmon phosphorus retention, excretion and reduction versus control using OptiPhos® at 500 and 750 OTU/kg feed. All treatments relative to the control group had a statistical difference.

Figure 5. Rainbow trout phosphorus retention, excretion and reduction versus control using OptiPhos® at 500 and 750 OTU/kg feed

The results presented in Figures 4 and 5 clearly show: 

• OptiPhos® at 500 - 750 OTU/kg feed significantly reduces phosphorus discharge into the environment in trout and salmon production systems.
• OptiPhos® can significantly reduce the current usage of inorganic phosphorus in salmonid feeds.
• OptiPhos® helps to minimise the environmental impact of salmonid aquaculture.

This article originally appeared on The Fish Site, 8 Dec 2020.