Captive Hemigymnus melapterus exposed to large numbers of cultured juvenile parasitic isopods ( Gnathia sp.) had significantly lower haematocrit (median 27·62% ± 5·83% inter‐quartile range) than uninfected, control fish (median 32·73% ± 4·90%). This study is the first to show that juvenile Gnathia sp. reduce total blood volume in H. melapterus . The low haematocrit in infected fish was most likely due to plasma replacing eryth...

Toxic ( Gobiodon spp.) and non‐toxic ( Paragobiodon xanthosomus ) gobies became infected with external parasites (gnathiid isopods) at equal rates in a laboratory experiment. Parasites were evenly distributed over the body of P. xanthosomus but were mostly confined to the fins of Gobiodon spp., where toxin glands are less abundant. Skin toxins were not associated with the rate of infection but their distribution did appear to...

The cleaner fish Labroides dimidiatus affected the pigmented monogenean parasite Benedenia lolo on the fish Hemigymnus melapterus (Labridae) held in aquaria. The effect of cleaner fish varied with the size class of fish; only small fish [ a posteriori size class L S )] exposed to cleaner fish had fewer monogeneans compared with fish not exposed to cleaner fish. The abundance of monogeneans on large fish ( a posteriori size cla...