# Mixtures of Algal Oil and Terrestrial Oils in Diets of Tiger Puffer (Takifugu rubripes)

## TL;DR

This study explores using algal oil mixed with poultry or rapeseed oil as a fish oil substitute in tiger puffer diets, finding it effective but with some intestinal health concerns.

## Contribution

The study introduces a novel mixing strategy of algal oil with terrestrial oils to replace fish oil in tiger puffer diets, addressing lipid composition limitations of algal oil alone.

## Key findings

- Mixed algal and terrestrial oils supported growth and health similarly to fish oil in tiger puffers.
- Algal oil increased DHA but reduced EPA and altered fatty acid profiles in fish tissues.
- Mixed diets affected intestinal gene expression and showed potential for intestinal health improvements.

## Abstract

With the rapid development of the aquaculture industry, finding alternative lipid sources to fish oil has become a key task for the aquafeed sector. Algal oil (AO) derived from Schizochytrium sp. is considered a highly promising alternative lipid source due to its rich content of long-chain polyunsaturated fatty acids (LC-PUFAs), particularly docosahexaenoic acid (DHA). Numerous studies have shown that AO can effectively support fish growth performance, immune function, and health status when partially or completely replacing fish oil, but the sole use of AO makes the diets lack saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs), which are good energy substrates. This study aims to further investigate the efficacy of AO in diets of tiger puffer (Takifugu rubripes), when used in combination with terrestrially sourced oils rich in SFAs and MUFAs.

The n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) have a key role in maintaining fish growth and health. However, fish oil (FO), the main source of n-3 LC-PUFAs, is in relative shortage due to the rapid development of the aquaculture industry. In this study, we investigated the efficacy of replacing fish oil with mixtures of algal oil (AO) from Schizochytrium sp. and terrestrially sourced oils (animal oil poultry oil (PO) or vegetable oil rapeseed oil (RO)) in the diets of juvenile tiger puffer (average initial body weight 23.8 ± 1.51 g). An 8-week feeding trial was conducted using three experimental diets: a control diet containing 6% added FO (control FO-C) and two diets with 3% AO + 3% PO or RO (groups AO+PO and AO+RO, respectively), replacing FO. Each diet was fed to triplicate tanks with 25 fish in each tank. The weight gain, feed conversion ratio, body composition, and serum biochemical parameters were not significantly different among the three groups, except that the AO+PO group had a significantly lower muscle lipid content than the other two groups. The AO-added diets significantly increased the DHA content in whole fish, muscle, and liver samples but significantly reduced the EPA content. The oil mixture treatments significantly increased the contents of monounsaturated fatty acid (MUFA) but significantly decreased the contents of saturated fatty acids (SFAs) in the liver and whole fish samples. However, the MUFA and SFA contents in the muscle samples were not significantly different among the dietary groups. The diets with oil mixtures did not affect the hepatic histology but tended to result in the atrophy of intestinal villi. The treatment diets downregulated the hepatic gene expression of proinflammatory cytokines (il-1β and tnf-α) and the fibrosis marker gene, acta2. However, the AO+PO diet inhibited the intestinal gene expression of the tight junction protein, claudin 18. In the muscle, the treatment diets upregulated the expression of genes related to cell differentiation and apoptosis (myod, myog, myf6, myf5, bcl-2, and bax). In conclusion, Schizochytrium sp. oil in combination with terrestrial oils (poultry oil or rapeseed oil) can be an effective alternative to fish oil in the diets of tiger puffer, but the mixing strategy may be better modified in consideration of intestinal health.