Temperature Effect on Parasitism in Auricularia Larva of the Sea Cucumber Isostichopus fuscus: Implications for Aquaculturing and Management

A protozoa leads a rapid onset of symptoms, with high mortality rates in the rearing of the planktotrophic larvae of the tropical holothurian Isostichopus fuscus for aquaculture. This study aimed to determine the effect of temperature on the infection parameters and the larvae size with/without parasites in its five development stages: T1–EA (250–300 μm), T2–MA-I (300–600 μm), T3–MA-II (600–900 μm), T4–A (1.1–1.3 mm), and T5–LA (≈500 μm). Eight 500 L conical tanks with filtered and UV-sterilized seawater with 0.2 larvae mL−1 under two temperature treatments (low: 23.0 ± 2.5 °C, high: 27.0 ± 0.5 °C). Thirty larvae per replicate at intervals of 4–5 days were sampled until day 25. A total of 1200 larvae were examined, and a total of 21,715 parasites were counted. A total of 97% of parasites were found under low temperature conditions. The DSI and survival significantly varied in relation to the temperature and time. The highest prevalence and intensity, 62.5 ± 5.7% and 130.5 ± 13.0, respectively, were observed at T4 at low temperature. At 18 d, larvae without parasites were larger (1494.1 ± 52.2 μm) than larvae with parasites (1237.7 ± 24.4 μm, p < 0.05) at 25 d. These findings suggest that elevated temperature functions as a key regulator in mitigating parasitic infections in auricularia larvae of I. fuscus.