In vitro prediction of digestible protein content of marine microalgae (Nannochloropsis granulata) meals for Pacific white shrimp (Litopenaeus vannamei) and rainbow trout (Oncorhynchus mykiss)

Digestible protein (DP) contents of novel feed ingredients are required for test diet formulation and commercial feed production. Species-specific in vitro pH-Stat protein hydrolysis was used to predict the DP contents of three algal meals produced from a common lot of the marine eustigmatophyte microalga, Nannochloropsis granulata, for juvenile Pacific white shrimp (Litopenaeus vannamei) and rainbow trout (Oncorhynchus mykiss). Protein degree of hydrolysis (DH) and predicted protein apparent digestibility coefficients (ADCs) for Pacific white shrimp were statistically similar for all meals with average DH of 2.09% (P = 0.052) and predicted ADC of 74.6% (P = 0.053). Alternatively, meals processed by supercritical fluid extraction at 70 and 90 °C showed significantly (P < 0.001) higher DH and predicted ADC than the untreated base material for rainbow trout with average DH of 4.79% and predicted ADC of 87.0%, compared to 2.53% and 79.1%, respectively. Predicted protein ADC for all N. granulata meals was moderate for Pacific white shrimp (69-78%) and high for rainbow trout (79-88%) and therefore indicates their potential for use in fish and shrimp diets. Based on our results, we suggest DP values (dry matter basis) for similar N. granulata meals of 26% for Pacific white shrimp and 29% for rainbow trout.