SummaryAn outbreak of gnathiids in a captive fish population in a large exhibition aquarium is described, including a method for enumeration of the causative agent. This procedure for harvesting and counting the parasites was based on the positive phototropism of their larvae (zuphea and praniza). Water pumps with spotlights allowed capture of larva using a 200-micron plankton net. Harvested samples were rinsed with fresh water in the laboratory to immobilise the zuphea and praniza and thus facilitate the enumeration process by direct observation under a stereoscopic glass. The sampling method was found to be representative of the degree of infestation experienced by the entire aquarium system; this finding is very important as it allows the enumeration of different life-cycle stages (zuphea, praniza and adults). The outbreak was studied and the infestation monitored over a period of many years. Several substrates were assayed for the capture of gnathiid males, with identification of the causative parasite by such morphological characteristics as Gnathia maxillaris. Physical and chemical treatments were applied to mitigate the infestation. Selected to control the infestation and its lifetime in closed marine-water systems, the Trichlorfon was evaluated by chromatography.

No abstract

Aims:  Vibrio populations in the seawater supply and the water of seven exhibition aquaria that simulate various Mediterranean and tropical ecosystems were compared. The similarity of Vibrio populations in the intestine of various fish species, feed and water was examined. Resistance to the antibiotics used in fish health management was analysed for the dominant Vibrio isolates. Methods and Results:  Samples were collected for 1 year from seven exhibition tanks reproducing different ecosystems. The diversity and population similarity among vibrios were determined using a miniaturized biochemical phenotyping method. Similar Vibrio populations were found in the water supply and in the water of the Mediterranean ecosystems. However, different Vibrio populations were found in the water of tanks with tropical ecosystems. Vibrio populations in the water seemed to have a greater effect on the composition of intestinal Vibrio populations than those in feed. No resistance to antibiotics was observed, indicating their appropriate use for health management. Conclusions:  Water characteristics have a greater impact on the composition of Vibrio populations in aquaria and fish intestinal microbiota than bacteria in feed. Significance and Impact of the Study:  The microbiological monitoring water could provide valuable information for managing the health of exhibition aquaria.

Summary The eradication of the haematophagous isopod ectoparasite Gnathia maxillaris was not achieved after several years of physical elimination of larvae by filtration and chemical treatment with trichlorfon in a captive marine fish population in exhibition aquaria. In this study, different in vitro laboratory assays were performed to find effective alternative anti‐parasitic treatments to trichlorfon (lufenuron, emamectin benzoate, cypermethrin and abamectin). The lethal concentration 50 (LC50) values at 96 hr were calculated for each compound using both larval stages (zuphea and praniza); morphological deformities generated throughout the life cycle, reduction in egg laying and survival of adult forms were also determined. Abamectin, cypermethrin and emamectin benzoate proved effective at limiting further Gnathia maxillaris development, but their efficacy at eradicating an infestation in large tanks was not supported by laboratory assays. However, the use of lufenuron proved to be a good substitute for trichlorfon when treating this type of infestation in large‐volume tanks (LC50 55.8 mg m−3 for praniza). Routine lufenuron treatment once a month via an oral dose at 10 mg kg−1 body weight eradicated G. maxillaris from the exhibition aquaria.