Juvenile summer flounder,Paralichthys dentatus, mortalities in the western Atlantic Ocean caused by the hemoflagellateTrypanoplasma bullocki: evidence from field and experimental studies

Dynamics of the interaction between the parasitic isopod, Anilocra pomacentri, and the coral reef fish, Chromis nitida

Field and laboratory investigations into the effect of the parasitic isopod Anilocra pomacentri (Cymothoidae) on the population dynamics of the reef fish Chromis nitida (Pomacentridae) were carried out at Heron Island, Great Barrier Reef, Australia. Fish carried a single adult parasite just posterior and dorsal to the eye either to the right or to the left of the midline. The adult parasite was overdispersed among fish on patch reefs (dispersion factor, k = 0.69). Sequential field observations on a single cohort of fish showed that parasites significantly depressed growth, reproduction, and survivorship. The von Bertalanffy growth coefficients (a measure of somatic growth) were 0.10 for parasitized fish compared with 0.17 for non-parasitized fish. Female fish carrying the parasite produced only 12% of the number of eggs produced by non-parasitized fish of the same size. In the field, the mortality of infected juvenile C. nitida (LCF 15-30 mm) was estimated to be at least 88% in the first 70 days after recruitment of the fish. The mortality of uninfected recruits over the same period was 66%. In laboratory trials, the mortality associated with the infection of juvenile fish by larval parasites ranged from 78% for small fish (mean LCF 15.0 mm) to 28% for larger fish (mean LCF 24.9 mm) within 4 days of experimental infection. This is one of the few studies that evaluates the effect of a parasite on a population of fish in the field.

The seasonal antibody response in juvenile summer flounder (Paralichthys dentatus) to the hemoflagellate Trypanoplasma bullocki

An immuno-blot assay was used to investigate the serum antibody response in flounder injected with formalin-killed flagellates (immunized) and those injected with saline (control) and challenged with live T. bullocki after 21 days. Fish were held at 20 degrees C and at ambient temperature from October through June. At 20 degrees C immunized fish had significantly higher antibody titers than control fish, but immunized fish were not protected from infection with T. bullocki. At ambient temperature, after initial flagellate growth phase, antibody titer varied directly with temperature (2-25 degrees C) and T. bullocki intensity varied inversely with titer. Flagellates were eliminated from the peripheral circulation in both immunized and control fish when antibody titer peaked in May. Recovered fish were immune to homologous challenge for at least one year.