Evaluation of microalgae as a potential fishmeal replacement in the diet of oreochromis mossambicus

Algae biomass from strains isolated from Corpus Christi, TX water were evaluated as ingredients to replace fishmeal in diets fed to Oreochromis mossambicus. Strains were selected based upon ability to be cultured on inexpensive nutrient media, biochemical composition, and ability to achieve productivity of ≥ 0.10g/L. Further selection involved evaluation of test ingredients for apparent dry matter, protein, ingredient, and amino acid digestibility when fed to juvenile (~30g) tilapia. Digestibility diets consisted of 69% reference diet, 1% Cr2O3 as an inert marker, and 30% algal test ingredient. Apparent dry matter digestibility ranged from 50.7±0.02% to 70.6±0.07% in the M. salina and Spring mix 2014 (Spmix), respectively. The Platymonas sp. and the Spmix diets exhibited the highest dry matter digestibility (69.3±5.5% and 70.6±3.9%, respectively). The dry matter in the Cylindrotheca sp. (57.9±3.5%) and the M. salina (50.7±8.5%) diets were the least digestible. Results showed that there were no significant differences in regards protein digestibility in the formulated diets (n=3). Also, there were no significant differences between the digestibilities of the ingredients (ADCI). The Platymonas sp. and the Spmix had the highest ADCI 83.1 ± 30.0% and 85.3 ± 24.6%, respectively. Methionine was 93.0% digestible in M. salina, and lysine digestibility was highest in Spmix (88.5±0.46%). In a subsequent 30-day feeding trial, ten ~0.170 mg tilapia were fed diets in which Spmix and Platymonas sp. (P) replaced various levels of fishmeal (0, 20, 40, 60, 80, 100%) in diets containing 40% crude protein. Weight gain (%), specific growth rate (SGR), final body weight, feed conversion ratio (FCR), protein efficiency ratio (PER), and percent survival were evaluated (n=5). Survival ranged from 96-100%. There were no significant differences in percent weight gain in the fish fed P20%-P80% diets. The FCR of the fish fed P20% and P40% were different from those fed the P100% diet (P=0.0145). The PER of fish fed P20%, P40%, and P80% were also significantly different from that of the fish fed the P100% (P=0.0214) diet. Fish fed the P100% diet had the lowest FCR (1.19±0.14). All performance indices were similar for tilapia fed the Spmix diets. Results showed that both test ingredients could be used to replace fishmeal at high levels of dietary inclusion, 80% for Platymonas sp. and 100% for Spmix. This indicates high potential for replacement of fishmeal in tilapia feeds with marine microalgae.