Abstract
Several hundred smooth lumpsuckers (Aptocyclus ventricosus) were hatched from an egg mass collected in Resurrection Bay in April 2012 and reared with excellent survival in an open seawater system. The larval fish were fed enriched Artemia nauplii until they grew large enough to eat appropriately sized thawed seafood (primarily pacifica and superb krill) supplemented with squid and silversides. Growth was steady with only occasional drop outs. Seawater was pre-filtered through high-rate sand filters prior to entering the back-holding tank and once through a felt bag filter for exhibit tanks. Fish in back-holding had been transferred from a smaller holding tank in September 2014. Summer water temperatures were warmer than usual (> 10°C), which persisted longer into the fall than normal. The pH was 8.02 and salinity was 30.5–31.0 ppt.
In November 2014, fish were being held in two exhibits and one back-holding tank at densities of 0.04, 0.83, and 0.11 fish/L respectively, when a sharp increase in mortalities was noted in the back-holding tank. Affected fish exhibited aberrant swimming behavior, mottled discoloration, edema and exophthalmia, and usually died acutely. Necropsies showed no significant external parasites, but mild loss of tissue was noted on fins. Edema, ascites, and serosal and mucosal reddening were noted in multiple organs. Gastrointestinal contents varied from normal digesta to empty. Histopathology revealed lesions consistent with acute bacterial septicemia, with many extracellular and phagocytized bacteria in multiple tissues that were consistent with marine Vibrio. Aerobic microbial culture produced oxidase-positive, Gram-negative, curved (variable), motile bacilli that were sensitive to oxytetracycline (OTC) and the vibriostatics novobiocin and 0/129. Viral cultures were negative.
Ultraviolet (UV) irradiation was implemented downstream of the sand filters after mortalities began. Within three weeks, 84% of the fish in the back-holding tank had died. Remaining survivors were transferred to a smaller tank. Only a few mortalities with symptoms similar to those in the back-holding tank were observed in the exhibit tanks. A trial bath of nitrofurazone was used on four fish pending laboratory reports. Once Vibrio was identified, treatment began on remaining survivors in the back-holding area using medicated baths (OTC at 95 mg/gal for four hours daily for four days, rest for two days and then repeat) and oral OTC powder in food (6 mg of powder per fish per day).1 Display fish were treated with only oral OTC due to issues with dissolved oxygen and temperature when the flow was decreased for bathing.
There is little published information on the captive biology and natural history of this species. In particular, the habitat and feeding requirements during juvenile to adult transition are largely unknown. Eggs and adults of the Atlantic lumpsucker Cyclopterus lumpus have been raised commercially.2 One study found 12 different bacteria associated with diseased lumpfish in Norway including vibriosis, pasteurellosis, and atypical furunculosis.3 This is consistent with our diagnosis of vibriosis.
The smooth lumpsuckers in our facility appeared to tolerate the OTC treatments well and mortalities decreased rapidly within one week.
Acknowledgments
The authors thank Richard Hocking and the Alaska SeaLife Center Aquarium Department and Veterinary Sciences staff for their excellent husbandry care of the smooth lumpsucker collection and their expertise and dedication in instituting treatments. We are grateful to the staff of the Alaska Department of Fish and Game Division of Commercial Fisheries Fish Pathology Section for their assistance in generating necropsy and culture reports including photomicrographs used for this poster.
* Presenting author
Literature Cited
1. Noga E. Fish Disease: Diagnosis and Treatment. 2nd ed. Ames, IA: Wiley-Blackwell; 2010: 382–383.
2. Davenport J. Synopsis of Biological Data on the Lumpsucker Cyclopterus lumpus (Linnaeus, 1758). FAO Fisheries Synopsis #147 (Food and Agriculture Organization of the United Nations); 1985.
3. Karlsbakk E, Alarcon M, Hansen H, Nylund A. Sykdom og parasitter i vill og oppdrettet rognkjeks. In: Bakketeig IE, Gjøsæter H, Hauge M, Sunnset BH, Toft KØ. (red.) Havforskningsrapporten. Fisken og havet, særnummer. 1–2014 (English summary); 2014.