Feeding ecology of the fish ectoparasite Gnathia sp. (Crustacea: Isopoda) from the Great Barrier Reef, and its implications for fish cleaning behaviour

The feeding rate of a parasitic gnathiid isopod on fish was examined. Individual fish, Hemigymnus melapterus, were exposed to gnathiid larvae and sampled after 5, 10, 30, 60, and 240 min. I recorded whether larvae had an engorged gut, an engorged gut containing red material, or had dropped off the fish after having completed engorgement; variation among sampling times and larval stages was analyzed using generalized linear mixed model analyses. The likelihood that larvae had an engorged gut increased with time and varied with larval stage. First stage (1.45 mm) larvae. After 30 min, however, most (>93%) larvae had an engorged gut regardless of their larval stage. The likelihood of red material in the gut of third stage larvae increased over time (46% after 30 min, 70% after 60 min, and 86% after 240 min) while that of first and second stage larvae remained relatively low (

Cleaner fish Labroides dimidiatus reduce 'temporary" parasitic corallanid isopods on the coral reef fish Hemigymnus melapterus

To determine if cleaners affect 'temporary' parasitic corallanid isopods (Argathona macronema) on fish, we used caged fish Hemigymnus meldpterus (Labridae) on 5 patch reefs on Lizard Island, Great Barrier Reef, and removed all cleaner fish Labroides dimidiatus (Labridae) from 3 of the reefs, In a short-term experiment, fish were sampled after 12 or 24 h, at dawn and sunset respectively, and in a long-term experiment they were sampled after 12 d at sunset. Isopod prevalence, abundance and size were measured. In the short-term experiment, on reefs without cleaners the prevalence of A. macronema was higher after 24 h than after 12 h while on reefs with cleaners, prevalence was low at all times, Although the abundance of A, macronema did not vary after 12 and 24 h, when combined over the 24 h, the effect of cleaners was significant with only 2 % of all the A. macronema found on reefs with cleaners. Cleaners had no effect on the size frequency distribution of A. macronema in the short-term experiment, most likely because fish had so few isopods on reef with cleaners. In the longer-term experiment, the effects of cleaners on isopod prevalence and abundance were less clear. Their effect on isopod size was, however, significant with smaller parasites on reefs without cleaners. The reduction of isopod prevalence and abundance by cleaner fish over a period of hours may explain why these A, macronema are rare on wild fish. Our findings support the idea that cleaning is beneficial to clients and has important implications for the control of parasites of fish farmed in cages,

Reproductive and feeding ecology of parasitic gnathiid isopods of epaulette sharks (Hemiscyllium ocellatum) with consideration of their role in the transmission of a haemogregarine

Epaulette sharks Hemiscyllium ocellatum were surveyed on Heron Island, Great Barrier Reef, Australia for gnathiid isopods and protozoan (haemogregarine) parasites to determine the prevalence and intensity of infection and to investigate the potential role of gnathiids as vectors of these haemogregarines, the first such study carried out on elasmobranchs. Juvenile gnathiids were collected and quantified using a novel non-invasive and chemical-free technique and gnathiid squashes were examined for haemogregarine developmental stages. The feeding and reproductive ecology of the Gnathia spp. was investigated to better understand the relationship between gnathiids and haemogregarines. Gnathiids were found on all sharks and intensities ranged between two and 66. Only third-stage gnathiid juveniles were found, which fell into two size groups (A and B). These juveniles remained attached to H. ocellatum for up to 17 days, the longest period of attachment yet recorded for gnathiids. Group A female gnathiids produced broods of 45-187 (median = 120) first stage juveniles from between 54 and 82 days (median = 63 days) after detachment. First stage juveniles survived for an average of 15.8 +/- 0.1 (SEM) days without feeding. The prevalence (6.7%) and parasitaemia (usually

Parasitic isopods (Gnathia sp.) reduce haematocrit in captive blackeye thicklip (Labridae) on the Great Barrier Reef

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 erythrocytes lost as a result of isopods feeding on fish blood. (c) 2005 The Fisheries Society of the British Isles.

Hematozoa of teleosts from Lizard Island, Australia with some comments on their possible mode of transmission and the description of a new hemogregarine species

Little is known of the blood parasites of coral reef fishes and nothing of how they are transmitted. We examined 497 fishes from 22 families, 47 genera, and 78 species captured at Lizard Island, Australia, between May 1997 and April 2003 for hematozoa and ectoparasites. We also investigated whether gnathiid isopods might serve as potential vectors of fish hemogregarines. Fifty-eight of 124 fishes caught in March 2002 had larval gnathiid isopods, up to 80 per host fish, and these were identified experimentally to be of 2 types, Gnathia sp. A and Gnathia sp. B. Caligid copepods were also recorded but no leeches. Hematozoa, found in 68 teleosts, were broadly hemogregarines of 4 types and an infection resembling Haemohormidium. Mixed infections (hemogregarine with Haemohormidium) were also observed, but no trypanosomes were detected in blood films. The hemogregarines were identified as Haemogregarina balistapi n. sp., Haemogregarina tetraodontis, possibly Haemogregarina bigemina, and an intraleukocytic hemogregarine of uncertain status. Laboratory-reared Gnathia sp. A larvae, fed experimentally on bruslitail tangs, the latter heavily infected with the H. bigemina-like hemogregarine, contained hemogregarine gamonts and possibly young oocysts up to 3 days postfeeding, but no firm evidence that gnathiids transmit hemogregarines at Lizard Island was obtained.

Emergence rates from the benthos of the parasitic juveniles of gnathiid isopods

Variation in the rate at which parasitic gnathiid isopod juveniles emerged from the benthos at Lizard Island, Great Barrier Reef, Australia, was examined (I) every 4 or 8 h throughout the day and night over a 24 h period, (2) over a 12 h period during the day or night, and (3) during different lunar phases (weeks). The number of gnathiids sampled per 4 or 8 h was low, with only 30% of the traps containing gnathiids and the abundance ranging from 0 to 3 gnathiids m(-2). The number of gnathiids that emerged over 12 h, in contrast, ranged from 0 to 36 m(-2). During the third and fifth weeks sampled, more gnathiids emerged during the day than at night. This coincided with the full moon and new moon. Most gnathiids that emerged from the reef during the day (98 %) had not fed, in contrast to those sampled at night (71%). Of the gnathiids with no engorged gut, most (97 %) of those collected during the day were small (II. mm) compared to those collected at night (19%), the latter being mostly >1 mm. Of the gnathiids with an engorged gut, most were sampled at night (83 %) and 97 % were >1 mm in size. These percentages suggest differences in the emergence behaviour among Life stages or species of gnathiids. This study, which shows that gnathiids do emerge during the day and supports other studies showing that gnathiids also attack fishes during the day, has important implications for understanding the role of cleaner fish and their main food source, gnathiids, as it shows there is a constant source of gnathiids emerging from the reef during the day and night in search of hosts.