Effect of Argulus infestation on oxygen consumption, total protein and glucose in three freshwater ornamental fishes

Abstract

Fish lice of the genus Argulus are widespread crustacean ectoparasites and a recurrent health problem in the ornamental fish trade, yet their effects on host physiology and tissue biochemistry in commonly traded species are poorly documented. This study compared oxygen consumption, total tissue protein and tissue glucose between uninfected and Argulus-infected goldfish (Carassius auratus), sailfin molly (Poecilia latipinna) and common carp (Cyprinus carpio). Oxygen consumption was estimated from the decline in dissolved oxsygen in the holding water, protein was estimated by the Folin–Ciocalteu method and glucose by the anthrone method. Groups were compared with Welch’s unequal-variance t-test, with Holm correction across species, and a two-way analysis of variance (species × infection status) was used to test the overall infection effect and its consistency among species. Infection was associated with a marked and consistent depletion of tissue biochemical reserves. Total protein and glucose were substantially lower in infected fish of all three species, the differences remained significant after multiplicity adjustment, and the standardised effects were very large. Infection status was the dominant source of variation in both variables, although the size of the decline differed among species. In contrast, oxygen consumption did not differ significantly between infected and uninfected fish; the direction of change varied among species and variability was high relative to the sample size. These results show that Argulus infection depletes protein and carbohydrate reserves in ornamental fishes, consistent with the metabolic cost of blood feeding and stress, and they do not support the view that infection consistently reduces respiration. Larger, replicated studies with quantified parasite load, blood chemistry and histology are needed.