Abstract
Aurantiochytrium sp. is a heterotrophic microorganism that produces docosahexaenoic acid (DHA), thus being considered as a possible replacement for fish oil in aquafeeds. We investigated the effect of Aurantiochytrium sp. meal (AM) dietary levels (0, 5, 10, 20, and 40 g kg−1) on Nile tilapia body and hepatopancreas fatty acid (FA) profile, body FA retention, somatic indices, and morphophysiological changes in the intestine and hepatopancreas, after feeding Nile tilapia juveniles (average initial weight 8.47 g) for 87 days at 22 °C. The 10AM diet was compared to a control diet containing cod liver oil (CLO), since their DHA concentration was similar. Within fish fed diets containing increasing levels of AM, there was a linear increase in n-3 FA content, especially DHA, which varied in the body (0.02 to 0.41 g 100 g−1) and hepatopancreas (0.15 to 1.05 g 100 g−1). The morphology of the intestines and hepatopancreas was positively affected in AM-fed fish. Fish fed 10AM showed less accumulation of n-3 FAs in the body and hepatopancreas when compared to fish fed CLO. Therefore, AM is an adequate substitute for fish oil in winter diets for Nile tilapia, with the supplementation of 40AM promoting the best results regarding intestine and hepatopancreas morphophysiology.
Highlights
Fish are ectothermic organisms; their body temperature is influenced by water temperature, which affects their metabolic rate, feed consumption, feed conversion, and other physiological functions [1]
Our findings show that for Nile tilapia kept at cold, suboptimal temperature, dietary supplementation with 10 g kg−1 Aurantiochytrium sp. meal (AM) improved growth by 16%, in addition to improving feed efficiency, specific growth rate, and apparent net protein retention when compared to fish fed a diet without supplementation [15]
Docosahexaenoic acid concentration increased from 0.02 to 0.41 g 100 g−1 in fish fed 0AM and 40AM, respectively
Summary
Fish are ectothermic organisms; their body temperature is influenced by water temperature, which affects their metabolic rate, feed consumption, feed conversion, and other physiological functions [1]. Fish may use behavioral responses to overcome low temperature, fish under farming conditions cannot use such natural responses. This is the case in pond or cage farming situations where fish may be subjected to extreme temperature fluctuations [3]. As a primary response to low temperature, fish increase serum cortisol and catecholamine levels; as a secondary response, metabolic changes may occur [3]. These adaptations are commonly used as indicators of short‐term cold responses [4]. If low water temperatures persist for longer periods, the continued stress can trigger tertiary responses, causing physiological changes that can lead to mortality [5]
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