Parasitic isopod Anilocra apogonae, a drag for the cardinal fish Cheilodipterus quinquelineatus

Abstract

Cymothoid isopods Anilocra apogonae are regular ectoparasites of the cardinal fish Cheilodipterus quinquelineatus on the Great Barrier Reef. To determine whether this large isopod, attached to the head of the fish, affects the physiology and behaviour of its host, we conducted morphological measurements to obtain a condition index and several laboratory experiments on fish with and without isopods. The condition index did not vary between parasitised and non-parasitised wild fish. However, we found that parasitised fish lost more weight than unparasitised fish when fed a low food ration. Parasitised fish also had a higher rate of oxygen consumption than non-parasitised fish. When maintaining body posture in calm water, parasitised fish had an elevated pectoral fin beat frequency, probably because the isopod attaches asymmetrically, causing an asymmetrical weight balance for which the fish needs to compensate. Moreover, the sustained aerobic swimming speed as well as the swimming endurance at high water speeds were reduced in parasitised fish, possibly because of the drag from the parasite. The results suggest that parasites can have significant effects on fish even if this is not revealed by their body condition index in the wild. The metabolic effects found imply that parasitised fish may have to spend more time foraging to compensate for their higher metabolism. This could expose them to a higher risk of being eaten, a situation made worse by an impaired swimming ability that may reduce their capacity to escape a predator.

Ectoparasites increase swimming costs in a coral reef fish

“…The authors attributed this increase in energetic cost to the destabilizing effect of the asymmetrically attached parasite rather than to any physiological effects of parasitism. Indeed, they found that parasitized fishes used their pectoral fins more while at rest, presumably in order to maintain stability [5]. Our results suggest otherwise, because SMR did not increase when a model parasite was added, and we did not observe any change in pectoral fin beat frequency when fish were at rest (S. A. Binning 2012, unpublished data).…”

“…Parasitized fish, however, continued to consume an average of 24 per cent more oxygen on average when at rest than fish in the other three treatments. Ostlund-Nilsson et al [5] found similar increases in the resting metabolic rate of the cardinalfish, Cheilodipterus quinquelineatus, parasitized by a congeneric isopod, Anilocra apogonae. The authors attributed this increase in energetic cost to the destabilizing effect of the asymmetrically attached parasite rather than to any physiological effects of parasitism.…”

Benign effect of the fish parasitic isopod Ceratothoa cf. imbricata on Selenotoca multifasciata (Scatophagidae) from Australia

“…The first stage (mancae or early juvenile I stage) consists of a short phase as free-living organisms with good swimming ability, after which they need to find a fish to take their first meal (within 1 to several days) or they die (Tsai & Dai 1999, Mladineo 2003, Fogelman & Grutter 2008. Upon finding a suitable host, they initiate feeding, generally on blood and macerated tissues (mucus, epithelium and subcutaneous tissues) (Colorni et al 1997, BunkleyWilliams & Williams 1998, Horton & Okamura 2003, Östlund-Nilsson et al 2005. They attach to skin, fins, branchial or buccal cavities, or burrow into the musculature of fishes.…”

New occurrence of parasitic isopod Argathona sp. (Stebbing, 1905) from Epinephelus undulosus in the Tuticorin coast, Gulf of Mannar region

“…The parasites also affected the stability of their host requiring them to expend more energy just to keep upright (Ö stlund-Nilsson et al 2005). These isopods are potentially economically important parasites as they have been shown to cause detrimental effects on fish in captivity including growth inhibition, anaemia and death in smaller fish Adlard and Lester (1995).…”