Author: Dr. Norfarrah Mohamed Alipiah

Brown-marbled grouper (Epinephelus fuscoguttatus) is a prized fish in Malaysia and across the Asia-Pacific, not only for its high market value but also as an important species in aquaculture. However, grouper farming faces a major threat: vibriosis, a bacterial disease caused mainly by Vibrio alginolyticus and Vibrio parahaemolyticus. Outbreaks of this disease can lead to serious losses for fish farmers.

To better understand how grouper fights back against this disease, researchers from the Aquatic Animal Health and Therapeutics Laboratory, Institute of Bioscience, Universiti Putra Malaysia (UPM) studied the fish’s natural immune defense system. Their work focused on special molecules called pattern recognition receptors (PRRs), which act like the “sensors” of the fish immune system.

PRRs are the body’s early warning system. They detect harmful microbes and alert the immune system to respond. In this study, four PRRs were investigated in grouper fingerlings: pglyrp5 (peptidoglycan recognition protein), tlr5 (Toll-like receptor 5), and two C-type lectins, ctlD and ctlE. These molecules are not unique to grouper, they are found in many animals, including humans that showing how fundamental they are in the fight against infections.

The research team exposed young groupers to either V. alginolyticus or V. parahaemolyticus and then tracked their survival, observed visible symptoms such as ulcers, and measured how strongly the PRRs were activated in different tissues.

The results showed that fish infected with V. alginolyticus had a 50% mortality rate, much higher than the 27% seen in fish infected with V. parahaemolyticus. In contrast, all control fish (not exposed to bacteria) survived. Severe ulcers developed in fish challenged with V. alginolyticus, confirming that this strain is more dangerous.

Interestingly, the fish’s immune system reacted within just 4 hours, even before the bacteria could be detected in the body. This demonstrates how PRRs act as the first responders, buying valuable time before other immune defenses take over. Among the four receptors studied, pglyrp5 showed the strongest reaction where its activity increased up to 73 times in the spleen of infected fish. This highlights its crucial role in detecting Vibrio bacteria.

These findings are important because they show how groupers naturally defend themselves against infections. By understanding these early immune mechanisms, scientists can design better strategies such as vaccines or immune boosters to protect farmed fish from deadly outbreaks.

The research also revealed that grouper immunity shares similarities with other animals, including humans. This reminds us that the basic building blocks of life’s defense systems are deeply connected across species.

Date of Input: 02/09/2025 | Updated: 02/09/2025 | azah