EMULSIFIERS DO LITTLE TO ENHANCE THE PERFORMANCE OF BARRAMUNDI Lates calcarifer

This study was designed to test the efficacy of choline chloride (CC), lecithin powder or lysolecithin on the performance of juvenile Barramundi (aka Asian seabass; stock weight = 230g). Six diets were formulated with the same basic ingredient structure, with major protein sources being fishmeal (20%), poultry meal (18%) and blood meal (10%). Lipid inclusion was dominated by poultry oil (18%) and fish oil (5%). Carbohydrate sources included wheat (15%) and de-hulled lupins (7%). Monosodium phosphate was incorporated in all diets at 1.2%. Choline chloride, lecithin and lysolecithin supplementation varied according to the experimental design and ranged from 0.1 to 0.6%, however the design was not factorial (see figure).

The 13 week saltwater experiment was performed under controlled conditions (water temperature ≈27°C) in an indoor laboratory with 3 replicate tanks assigned to each diet. The first stage of the study focused on feeding (apparent satiation for 89 days) and growth response. The second stage was dedicated to collecting faecal material in order to determine the digestibility of each feed (31 days). Fish were sacrificed at the conclusion of the trial for compositional analysis and to determine other biometric indices including condition factor, hepatosomatic index (HSI), viscerosomatic index (VSI) and fillet yield.

The individual growth rate of Barramundi was acceptable and ranged between 4.8 - 5.3g day^-1. There were no significant differences among growth rates due to different diets (mean SGR = 1.33% d^-1) and we found no significant difference between feed intake or FCR of different diets (all FCR < 1:1 as fed basis). Likewise, there was no evidence of any differences in condition factor, HSI, VSI or fillet yield among dietary groups. The apparent digestibility coefficients of diets were high, but there was no difference among diets with respect to dry matter (≈72%), lipid (≈95%) or gross energy (≈83%) digestibility. Interestingly, there was a significant difference in protein digestibility among diets, but it was difficult to relate this to the effect of single emulsifiers or the particular combination of emulsifiers examined in this study (see figure). Based on the results of the growth trial, it appears there is little advantage to adding choline chloride, lecithin or lysolecithin to feeds for Barramundi. Additional investigation of the data from this study is underway and will be discussed; particularly the digestibility of individual fatty acids and the retention of protein, lipid and energy in whole fish carcass. This data will shed further light on the efficacy of emulsifiers in aquafeeds for Barramundi, especially their role in enhancing lipid digestibility or as a source of phospholipids.