Effect of formalin treatment on the presence of ectoparasites and survival of Asian sea bass (lates calcarifer) fingerlings / Yusmarini Yusoff

The Asian sea bass (Lates calcarifer) or locally called ‘Siakap’ is an economically important fin fish in South East Asia including Malaysia. Fingerlings are produced by commercial hatcheries and the culture of the sea bass however is hampered by disease occurrences. The disease of the Asian sea bass is widely studied, relatively little information is available on the treatment using long-term formalin bath in 24 hours. Therefore, the present study was carried out to investigate the effectiveness of different formalin concentrations for the treatment of ectoparasites in Asian sea bass fingerlings. The survival of fingerlings, the levels of pH and dissolved oxygen were also evaluated. The formalin concentrations used in this study were 10 ppm, 20 ppm, 30 ppm and 40 ppm with control at 0 ppm. Three size groups were established: two, three and four-inch fingerlings and were treated by immersing them in formalin bath for 24 hours. The sea bass fingerlings treated were infected by Cryptocaryon irritans, Trichodina sp., unidentified ciliates and monogenea. The results revealed the effectiveness of the 30 ppm formalin bath to eliminate Trichodina sp., monogenea and unidentified ciliates. However, formalin bath was found ineffective to eliminate Cryptocaryon irritans regardless formalin concentrations. There was no significant difference (Kruskal-Wallis test, p<0.05) in the survival of fingerlings during the treatment (survival between 93.33% and 100%). Results showed 100% survival except for the three and four-inch groups treated in 40 ppm formalin bath, indicating the tolerance of the fingerlings to formalin concentrations during the treatment. There was a strong correlation between survival of four-inch sea bass fingerlings and the pH levels (Pearson’s correlation, r2 = 0.953).