Seawater ozonation and formalin disinfection for the larval culture of eastern rock lobster, Jasus ( Sagmariasus) verreauxi, phyllosoma

Abstract

The effects of seawater disinfection with continuous ozonation or with daily formalin treatment during flow-through culture, on the survival, growth, bacteriology and histology of eastern rock lobster, Jasus ( Sagmariasus) verreauxi, phyllosoma were determined. Survival from hatch to Instar II was highest and bacterial abundance was least in low ozonated seawater (containing 5 ppb ionised bromine, Br). By contrast, at high ozonation (45 ppb Br) and medium ozonation (15 ppb Br), 77% and 69% of larvae, respectively, suffered deformities at the moult to Instar II and starved to death. Histological examination of phyllosoma showed no differences in cuticular epithelium thickness but the digestive gland tissue of moribund deformed phyllosoma had significantly thinner tubule epithelium, the lumen was dilated, B-cells were more abundant and there was greater separation between the cuticular epithelium and distal tip of digestive gland tubules. In unozonated (Control) water, 66% of larvae died during Instar II probably resulting from a possible Vibrio infection. In a second experiment, survival to Instar III was highest at low ozonation or no ozonation without addition of formalin (0 ppm). Bacterial numbers were lowest in low ozonation with 0 ppm formalin treatments, compared to daily treatment with formalin at 10 ppm or above. A concentration of 250 ppm formalin killed all larvae by Instar III. In a final experiment, larval survival between Instar III to VI in low ozonated seawater was approximately 80% at formalin levels of 0 to 80 ppm, whereas all larvae treated with 160 ppm formalin died shortly after Instar V. Disinfection improved survival by minimising bacterial disease for the culture of phyllosoma to Instar VI without interrupting growth and development. The present study established that the optimum treatment for the culture of phyllosoma to Instar VI appeared to be low ozonation (5 ppb Br) with 10 ppm formalin.