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

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 <i>Chaetoceros</i> 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 <i>Chaetoceros</i> sp. extract, while the in vivo experiment (Phase Two) evaluated the immune response following an 8-week dietary supplementation with <i>Chaetoceros</i> sp. powder. In Phase One, an 8 mg/mL concentration of <i>Chaetoceros</i> sp. extract demonstrated an overall enhancement in lysozyme activity and lymphocyte proliferation. In Phase Two, tilapia fed a diet containing 2% <i>Chaetoceros</i> sp. showed significantly improved lysozyme activity, while the 5% supplemented group exhibited a significant increase in lymphoproliferation activity (<i>p</i> < 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 <i>Streptococcus agalactiae</i>. These findings highlight the immunomodulatory potential of the diatom <i>Chaetoceros</i> sp. as a functional feed additive for freshwater fish, particularly red hybrid tilapia, and suggest its positive impact on fish health management in aquaculture.