# In Vitro and In Vivo Evaluation of Chaetoceros sp. Immunomodulatory Effects in Red Hybrid Tilapia, Oreochromis spp

## TL;DR

This study shows that the microalga Chaetoceros sp. can boost the immune system of red hybrid tilapia, improving their survival against bacterial infections.

## Contribution

The study demonstrates the immunomodulatory effects of Chaetoceros sp. in red hybrid tilapia through in vitro and in vivo experiments.

## Key findings

- Chaetoceros extract increased lysozyme activity and lymphocyte proliferation in vitro.
- Fish fed a 2% Chaetoceros diet showed higher survival after a bacterial challenge.
- Supplementation improved immune responses without affecting growth performance.

## Abstract

Bacterial infections caused by Streptococcus agalactiae are a major challenge in tilapia aquaculture, leading to high mortality and economic losses. This study examined the immunomodulatory potential of the microalga Chaetoceros sp. in red hybrid tilapia. In the first phase, in vitro assays using fish blood and immune cells demonstrated that Chaetoceros extract at an optimal concentration enhanced lysozyme activity, which helps destroy bacterial cell walls, and promoted lymphocyte proliferation, a key component of adaptive immunity. Based on these findings, an in vivo feeding trial was conducted in the second phase. Tilapia were fed diets supplemented with Chaetoceros for eight weeks, resulting in improved lysozyme activity, stronger respiratory burst responses, and increased lymphocyte activity. Notably, fish fed a 2% Chaetoceros diet showed higher survival following a bacterial challenge with Streptococcus agalactiae. These results highlight Chaetoceros sp. as a promising natural immunostimulant to strengthen disease resistance and reduce reliance on antibiotics in aquaculture.

Diatoms are recognized as a valuable source of bioactive compounds that can stimulate the immune defense mechanisms of fish. This study aimed to assess the effects of Chaetoceros sp. in modulating the specific and non-specific immunity of red hybrid tilapia through in vitro functional assays, an in vivo feeding trial, and a bacterial challenge. The in vitro experiment (Phase One) examined the immune response of tilapia cells exposed to Chaetoceros sp. extract, while the in vivo experiment (Phase Two) evaluated the immune response following an 8-week dietary supplementation with Chaetoceros sp. powder. In Phase One, an 8 mg/mL concentration of Chaetoceros sp. extract demonstrated an overall enhancement in lysozyme activity and lymphocyte proliferation. In Phase Two, tilapia fed a diet containing 2% Chaetoceros sp. showed significantly improved lysozyme activity, while the 5% supplemented group exhibited a significant increase in lymphoproliferation activity (p < 0.05). Growth performance parameters were generally comparable among dietary groups, indicating that supplementation did not adversely affect growth. Notably, the 2% diet also enhanced fish survivability following a challenge with Streptococcus agalactiae. These findings highlight the immunomodulatory potential of the diatom Chaetoceros sp. as a functional feed additive for freshwater fish, particularly red hybrid tilapia, and suggest its positive impact on fish health management in aquaculture.