Evaluation of whole and lipid-extracted algae meals in the diets of juvenile red drum (Sciaenops ocellatus)

• The nutritional value of three lipid-extracted algal (LEA) products was evaluated.
• One algal species was evaluated as a whole product versus lipid-extracted.
• Algal co-products could replace up to 10% of dietary protein from common feedstuffs.
• Whole algae product proved a more nutritious product than LEA meals.

As aquaculture continues to expand, protein sources have become more costly and less available. Simultaneously, lipid-extracted algae (LEA) meals, which areco-products of bio-diesel production are becoming increasingly available. By integrating LEA into aquaculture diets, feed prices could possibly be lowered and bio-diesel production would have an additional revenue stream. Three separate feeding trials of either 7 or 8 week duration were conducted to evaluate four different algal meals as partial replacements for fishmeal and soy protein concentrate in diets for juvenile red drum (Sciaenops ocellatus) initially weighing 1.9, 5.2 and 13.0 g/fish. In the first trial, whole algae meal and LEA derived from Navicula sp. replaced 5 or 10% of the crude protein (CP) in the reference diet based on equal contributions from fishmeal and soy protein concentrate. Weight gain, feed efficiency (FE), survival, condition indices including hepatosomatic index, intraperitoneal fat ratio and muscle ratio as well as whole-body proximate composition were not significantly (P > 0.05) affected by substituting any of the algal products for fishmeal and soy protein concentrate in the reference diet. However, protein and energy retention values were significantly reduced in fish fed the diet with LEA meal included at 10% of dietary protein compared to fish fed the reference diet. Algal inclusion reduced the apparent digestibility coefficient (ADC) for CP by an average of 3%, while ADC for energy increased by an average of 8%. A second feeding trial evaluated incrementally higher levels of LEA derived from Chlorella sp., by replacing 5, 10, 20, and 25% of the CP in the reference diet. Weight gain, FE, and protein efficiency ratio (PER) were significantly reduced at substitution levels of 20 and 25% but there were no differences in condition indices or whole-body proximate composition. The third feeding trial evaluated smaller incremental levels of LEA derived from Nannochloropsis salina, replacing 5, 7.5, 10, and 15% of the CP in the reference diet. Weight gain, FE, survival, and PER as well as intraperitoneal fat ratio and whole-body lipid were significantly reduced in fish fed the diet with 15% substitution. Based on the results of these experiments, replacement of up to 10% of CP from fishmeal and soy protein concentrate with LEA was possible without causing significant reductions in fish performance. Overall, the whole algae product proved a more nutritious product than LEA meals when fed to juvenile red drum.