Industry Review
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Managing ectoparasites in farmed marine fish What is known of the life cycle of major sea lice, skin flukes and leeches and how to manage them.
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isease problems caused by various parasites in farmed fish are often overlooked mainly because they have less adverse impacts on production compared to viral and bacterial diseases. However, some of these parasites, if left uncontrolled, can cause significant production losses and affect the marketability of harvested fish leading to significant economic losses. The webinar, “Beauty and the Beast: Important parasites of fish” brought insights on how important parasites are in aquaculture, in particular to marine fish with three out of the four presentations focussing on sea lice, skin flukes and leeches. This webinar organised in December 2020 by the Fish Health Section (FHS) of the Asian Fisheries Society (AFS) was attended by 339 participants from at least 20 countries.
Dr Erlinda R. Cruz-Lacierda
“The aims were to raise awareness on the importance of parasites on both farmed and wild fish populations, to understand their mechanisms of infestation (including their life cycle), as well as disease prevention and control,” said Dr Eduardo Leano, Network of Aquaculture Centres in Asia. Dr Erlinda R. Cruz-Lacierda of the University of the Philippines Visayas (UPV) also encouraged the younger generation to continue research into fish parasitology, to add to the current information and to help industry better manage them.
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Pompano broo broodstock Trach Trachinotus blotchii infectedblotc with with Lepeophtheirus Lepe spinifer with spini exophthalmia exop (top left) and haemorrhagic (top areas on the haem operculum (top area right). oper
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Sea lice in the Philippines
In the Philippines, 21 species of sea lice have been identified. Two species, Caligus epidemicus and Lepeophtheirus spinifer are the most abundant and damaging to wild and farmed marine fish. An updated checklist from 1977-2019 showed infestations of C. epidemicus in milkfish Chanos chanos, seabass Lates calcarifer, mangrove snapper Lutjanus argentimaculatus, cobia Rachycentron canadum, green grouper Epinephelus coioides and siganids Siganus spp., among others. CruzLacierda said, “Occurring on the body surface of the fish, the prevalence of sea lice is high, reaching up to 100%. One study indicated that C. epidemicus showed a 100% prevalence in siganids Siganus guttatus and Asian seabass farmed in tanks and ponds. Lepeophtheirus spinifer was 100% prevalent in the pompano Trachinotus blochii farmed in cages. In siganid broodstock, symptoms are extensive erosion and haemorrhagic lesions, particularly on the anterior ventral part of the fish with 10% mortality. Pompano reared in net cages showed that L. spinifer and attached themselves to the body surface, fins and eyes. In severe infestations, there was exophthalmia and haemorrhagic areas on the operculum. Co-infection with the monogenean Neobenedenia spp. was also recorded on the eye. Pakingking et al. (2018) isolated Vibrio harveyii in L. spinifer infected pompano broodstock with exophthalmia. In 2018, Beluso et al. (2019) reported that L. spinifer infestation reached 220 individuals/fish when the water temperature was lowest at 27°C and salinity was highest
Pompano Trachinotus blotchii broodstock infected with Lepeophtheirus spinifer with exophthalmia (top left) and haemorrhagic areas on the operculum (top right). Pictures provided by Dr Erlinda R Cruz-Lacierda.
at 35ppt. Previous studies showed that the development and survival of sea lice were optimal at high salinity. CruzLacierda also discussed the prevalence of the different development stages of the sea lice. The whole life cycle of Caligus epidemicus covers 11 stages over 17 days, at 20ppt and 24-25°C (Lin and Ho, 1993). In the case of L. spinifer, the life cycle is completed within 6-7 days at 29°C and 30ppt (G. Erazo-Pagador, SEAFDEC AQD, pers. comm.). Skin lesions on the fish reduce market value of pompano. “There have been various treatment methods but the parasite remains a problem. Trichlorphon (Neguvon) is used to treat C. patulus on milkfish broodstock but this treatment has potential risks to both handler and environment,” said Cruz-Lacierda. Freshwater baths are ineffective as reinfection occurs after the fish return to the net cages. At SEAFDEC, trials using emamectin benzoate as treatment of L. spinifer on the pompano are ongoing.
March/April 2021 AQUA Culture Asia Pacific
