Supporting shrimp performance and
health in reduced fishmeal diets with Prosaf®
by Otavio Serino Castro and Nadège Richard, Phileo Lesaffre Animal Care, France
Fishmeal usage in commercial feeds has decreased from an average of 30 percent to 15 percent in recent years, subject to shrimp life stage, production systems and intensity. In addition, recent estimates suggest that fishmeal usage can be reduced further, potentially achieving average levels as low as 5 percent by 2025.
To nutritionally rebalance shrimp feed formulas, different strategies can be adopted using specific protein sources. These range from premium ingredients, such as soybean protein concentrate and krill meal, to lower grade alternatives like rapeseed meal, sunflower meal and rendered animal by-products, such as feathers and blood meal.
For each adopted strategy, nutritionists will assume different levels of risk when it comes to maintaining feed efficiency and growth performance. This is especially true for field conditions that impose additional challenges related to stress and shrimp health.
Challenges associated with low fishmeal diets for shrimp farming
Replacing fishmeal in shrimp diets can affect growth in several ways. Among the main factors which limit alternative protein utilisation are the reduced digestibility of essential nutrients; decreased attractiveness and palatability, and the presence of antinutritional factors that might not be completely inactivated or destroyed during feed processing.
The reduction of nutrient digestibility in alternative protein sources is generally linked to higher fibre and ash content; the presence of antinutritional factors, such as phytic acid which can bind essential nutrients, and losses which occur during ingredient storage and processing, which are generally caused by reduced freshness, high temperatures or chemical treatments.
Antinutritional factors also not only negatively impact shrimp performance by making nutrients unavailable, but also due to direct action on digestive and metabolic functions, enzymes activity, nutrients transport, etc.
The behavioral response of farmed shrimp to feed in the water, such as feed detection, orientation and movement, is moderated by the presence of chemical signals in the water. The most powerful of these attractants are small water-soluble molecules such as amino acids, small peptides, amines, nucleotides, nucleosides and quaternary ammonium bases. Reducing these key compounds, which are generally found in fishmeal and marine ingredients, can compromise the attractiveness and palatability of the feed concerned.
Another negative aspect is that using a slower and less efficient feeding process can lead to increased losses of nutrients in the feed by leaching, alongside reduced feed intake and poor feed conversion ratio. Furthermore, water and environmental quality can also be negatively impacted.
Identifying solutions to improve low fishmeal diets, while mitigating and neutralising any detrimental effects on shrimp performance and health, can be a valuable tool for the aquaculture feed industry, enabling them to extract the best use and value from alternative protein sources, especially plant-based raw materials.
Premium soluble yeast extract as an innovative tool to support sustainable aquaculture production beyond fishmeal replacement
Different yeast products have been used in relation to aquaculture nutrition alongside different target applications. These include inactivated and spent yeast (protein source), yeast cell wall (mycotoxin binder and immune-stimulation), purified B-glucans (immune training), purified nucleotides (nucleotides supplementation), etc. To address the growing protein challenge for the aquaculture industry, Phileo - Lesaffre Animal Care has invested in the research and development of a premium soluble yeast extract (Prosaf®), a product which is rich in free amino acids and low molecular weight peptides, qualities which can help support nutritionists who are working with reduced fishmeal diets.
Prosaf® benefits from being a primary culture of a selected proprietary baker"s yeast strain, produced under a standardised autolysis, solubilisation and purification process. This enables a high protein content yeast extract to be produced efficiently with a consistent composition, full safety control and traceability.
Containing a minimum of 63 percent crude protein, Prosaf® has a well-balanced essential amino acid profile consisting of more than 56 percent amino acids in the total composition (26% in the free form). Prosaf® is composed only of small peptides: 95 percent of the product is classified as being under 3.6 kDa with 45 percent being below 1.9 kDa. Glutamic acid accounts for 10.9 percent and nucleotides 7.7 percent of the total composition.
Bringing all these qualities together, Prosaf® was selected to undergo a battery of tests to enable it to be validated and launched for use by aquaculture feed manufacturers in their feed formulation strategies.
Prosaf® application in shrimp
A three-phase scientific project was carried out to validate and prove the efficacy and potential of Prosaf® supplementation in low fishmeal diets for shrimp. During phase one, the In vivo digestibility of the product was assessed to assure the bio-assimilation of the nutrients. This featured a trial application of the indirect method using yttrium oxide as a marker in 14g shrimp, demonstrating Prosaf"s digestibility for crude protein at 89 percent, lipid 90 percent and energy 83 percent. The average essential amino acid digestibility was higher than 95 percent.
A further trial evaluated the impact of increasing dosages of Prosaf® (0.5% to 2.5%) in low fishmeal diets (LFM, 5%) on total diet digestibility, compared to a high fishmeal diet (HFM, 15%). Prosaf® supplementation was effective in restoring protein digestibility in LFM to the same level as for HFM. Usage at 2.5 percent significantly improved protein digestibility compared to LFM. These results prove the high bio-availability of the product"s protein content and its positive impact when included in feeds.
A trial carried out during phase two was designed to assess the effect of Prosaf® on shrimp feed consumption preference. A paired trial using a low fishmeal diet (3%), fed both with and without Prosaf® supplementation (2%), under a simultaneous feeding regime, was used to measure feed consumption preference as assessed in 13g-shrimp over a period of 15 days (two meals per day). Feed supplemented with Prosaf® achieved significantly higher feed intake compared to the LFM diet, being consistently consumed at a higher rate on a daily basis.
A third trial was conducted to evaluate the impact of Prosaf® supplementation on shrimp growth and health in LFM diets (5%), compared to an HFM group (15%). Shrimp fed on the LFM diet recorded a numerically lower body weight compared to the HFM group. The supplemented diets (0.5 and 2.5%) delivered a final weight which was statistically comparable to the HFM group. Prosaf® at 2.5 percent significantly increased the final body weight of shrimp compared to the control. The same response was observed concerning shrimp specific growth rate. No statistical differences were found in feed conversion rate results, although a trend towards a decrease was observed in response to increasing Prosaf® supplementation.
Some health parameters also improved significantly with both inclusion levels of Prosaf. Total hemocytes counts and phenoloxidase activity in the haemolymph were increased with Prosaf® supplementation in the LFM diet, demonstrating additional benefits to the animals. Prophenoloxidase, in the group supplemented at 2.5 percent, was also numerically superior, even when compared to the HFM diet.
Conclusion
Prosaf® as a premium functional ingredient can be an innovative and cost-effective tool to reduce aquaculture industry risks when developing strategies to support the rational utilisation of alternative proteins while still maintaining feed efficiency and optimum performance.
