Comparative Evaluation of Nannochloropsis oceanica Oil and Conventional Oils on Survival, Growth, and Immunity in Nursery Rohu (Labeo rohita): Towards Sustainable Aquaculture Feeds

A. Mohanty¹KC Das¹Rakhi Kumari¹Nitish K. Chandan¹S. Nandi¹P. K. Sahoo¹Arumugam Muthu^2*

• ¹Central Institute of Freshwater Aquaculture (ICAR), Bhubaneswar, India
• ²CSIR National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram, India

Nannochloropsis oceanica is a marine microalga recognized for its promising potential, owing to its exceptional ability to accumulate significant amount of polyunsaturated fatty acids, particularly omega-3. Under typical farming practices, the survival rate of rohu from spawn to fry is about 25-30%, while from fry to fingerling, it ranges from 40-50%. The lack of access to easily digestible quality nutrients is a primary factor constraining growth rates and compromising survival in critical nursery phases of carp culture. A comparative assessment was conducted to evaluate the efficacy of four distinct dietary oil sources: fish oil, microalgae oil (derived from Nannochloropsis oceanica), linseed oil, and sunflower oil on growth performance, survival, non-specific immune responses, and gut enzymatic activity in nursery-reared rohu (Labeo rohita). Four iso-nitrogenous and iso-lipidic experimental diets were formulated, each incorporating a distinct oil source: fish oil (FO), Nannochloropsis oceanica algae oil (AO), linseed oil (LO), or sunflower oil (SFO) and were randomly assigned to triplicate groups of nursery-reared rohu. From a total of 12 tanks (each with a capacity of 2000 L), three tanks were randomly allocated to each treatment group. A stocking density of 2000 rohu spawn per tank was maintained, and the experiment was conducted for three weeks following a completely randomized design. Over the three-week trial, during which fish were fed twice daily, the algae oil treatment yielded the highest survivability, whereas the fish oil treatment resulted in the superior growth rate for nursery-stage rohu. Similarly, analysis of gut enzyme activities amylase, protease, and lipase revealed that amylase activity was highest in nursery rohu fed with fish oil, while lipase activity was highest in those fed with algae oil. There was no significant difference in nonspecific immunity parameters like lysozyme, haemolytic, haemagglutination and myeloperoxidase activity between treatment groups. This demonstrated that algae oil derived from N. oceanica is a superior sustainable alternative to plant oils and offers a feasible partial or complete substitute for fish oil in nursery diets for rohu, aimed at optimizing survival rates, despite yielding marginally lower growth performance relative to fish oil-based diets.