A CAUTIONARY TALE FOR FORMULATORS - HOW ENVIRONMENTAL OR FARMING CONDITIONS MIGHT NEGATIVELY IMPACT DIET PERFORMANCE EVEN WHEN THEY UTILISE PREMIUM QUALITY RAW MATERIALS: THE EFFECT OF RESTRICTED FEEDING ON PERFORMANCE OF ASIAN SEABASS Lates calcarifer

When one traditionally thinks about dietary requirements, one tend to focus on the amount of nutrients required in the feed to give optimal performance.  However, when conditions are sub-optimal and intake is reduced, a previously adequate feed can become limiting, particularly with some of the amino acids and micronutrients.  Furthermore, during periods of high temperature, it has been shown in Asian seabass (Lates calcarifer), that the maintenance protein and energy requirement increases dramatically while the utilisation decreases¹.  In addition, Asian seabass above 33^oC show a significant reduction of feed intake and commensurate growth rate².

Much of the data published therefore is from studies where conditions are optimal and feed intake is not restricted and the focus is on the level of a nutrient in the feed rather than the nutrient intake in grams per fish.  In order to understand the impact of a single raw material under a restricted ration, a pair fed experiment was devised using juvenile Asian seabass where a high quality poultry meal (HQP) sequentially replaced a lower quality poultry meal (LQP). Five diets were formulated to by isoenergetic and providing all nutrients in excess of requirements for Asian seabass. A slight restriction of the satiated response of the fish fed the  highest inclusion of LQP was used to determine the feeding level of all treatments.  Apparent dietary digestibility of protein, energy, lipid, dry matter and methionine all increased with increasing HQP addition, however, surprisingly, growth decreased and FCR increased.  In conclusion, the restricted feeding ration had a negative impact on performance and micronutrients rather than macro-ingredients were investigated further.  This work highlights the dearth of information in the area of nutrient requirements in Asian seabass.

1. Glencross, B.D., Bermudes, M., (2011a). Effect of high water temperatures on the utilisation efficiencies of energy and protein by juvenile barramundi, Lates calcarifer. Fisheries and Aquaculture Journal

2. Bermudes, M., Glencross, B.D., Austen, K., Hawkins, W., 2010. Effect of high water temperatures on nutrient and energy retention in barramundi (Lates calcarifer). Aquaculture 306, 160-166.