Evaluation of Histopathological Changes in Cantang Groupers’ Brain and Gill Infected with Streptococcus Iniae

Cantang hybrid grouper is the result of hybridization between female Macan grouper (Epinephelus fuscoguttatus) and male Kertang grouper (Epinephelus lanceolatus). Hybrid fish have better performance in terms of growth, resistance to diseases, and tolerance to environmental factors, compared to the parents. One of the diseases that can attack fish is an infection induced by Streptococcus iniae (S. iniae), which is quite a dangerous bacterium since it can cause mass death of fish. The present study aimed to investigate the pathological changes of the brain and gill of Cantang hybrid grouper (Epinephelus fuscoguttatus and Epinephelus lanceolatus) infected with S. iniae. A total of 180 groupers from the Management Unit of Brackish Water Aquaculture, Situbondo, Indonesia, were included in the current study with a length of 7 cm. The experimental study was conducted using a complete randomized design, including three treatments and three repetitions for each one (n = 20). The main parameters to observe the histopathological changes in the fish internal organs, namely the gill and the brain at the beginning and the end of the study. Moreover, the supporting parameter was the water quality which included the temperature, oxygen content, pH, and salinity. Several observations including the pathogenicity test, Lethal Dosage 50 test, observation of clinical symptoms, and observation of histopathology were done during the treatment. The obtained results were indicative of the histopathology damages in the brain and gill tissues of the Cantag hybrid groupers infected with S. iniae. Different scores of lesions, infiltration, congestion, and degeneration were indicated in the brain tissue. Furthermore, the gill damages consisted of hyperemia, congestion, and infiltration. In conclusion, Cantang hybrid groupers (Epinephelus fuscoguttatus and Epinephelus lanceolatus) infected with S. iniae indicated the clinical symptoms, anatomical pathology, and histopathological changes.