Gnathia maxillaris infestation in exhibition aquaria: control and treatment strategies

Abstract

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.

Antiparasitic Effect of Formalin, Trichlorfon, Hydrogen Peroxide, and Copper Sulfate on the Parasitic Isopod <i>Caecognathia coralliophila</i>

“…Brandal and Egidius (1979) used Neguvon for the treatment of salmon lice in farmed salmon in Norway. Hispano et al (2013) succeeded in eliminating Gnathia maxillaries in aquaria and suggesting the bath treatment within the range of 0.3-0.5 ppm. In the present study, trichlorfon was used on a trial basis to kill C. coralliophila, and the in vivo experiment revealed that trichlorfon killed all of the larval parasites, even at a concentration of 0.2 ppm (Table 4).…”

“…Gnathiid infection in aquaculture systems is not common in Malaysia. However, there have been reports of gnathiid outbreaks in Europe (Marino et al, 2004;Hispano et al, 2013) and Japan (Yoshida, 1988).…”

“…Studies of treatments for crustacean isopod infections are more commonly carried out using cymothoidae; however, the study on the control of gnathiids is limited (Hispano et al, 2013). The purpose of this study therefore was to evaluate formalin, trichlorfon, hydrogen peroxide, and copper sulfate as potential treatments for C. coralliophila.…”

Evaluation of chemical treatments to mitigate or eradicate Gnathia maxillaris infestations

“…One water pump (15 m 3 hr −1 ) with a spotlight was located in the exhibition tank. The water was pumped through the plankton net, and zuphea and praniza were harvested using a 3 ml plastic Pasteur pipette where the tip was cut to avoid damage to the larvae, as previously described (Hispano et al., ). The praniza (attached to hosts) were also obtained directly from infected fish [mainly sunfish ( Mola mola ) and conger eels ( Conger conger )] using the Pasteur pipette.…”

“…Gnathia maxillaris, a crustacean isopod belonging to the family Gnathiidae, is a haematophagous ectoparasite that feeds on the blood and tissue fluids of fish (Jones & Grutter, ; Smit & Davies, ). Infestations of G. maxillaris in fish populations can cause significant losses in both captive (Giannetto et al., ; Hispano, Bultó, & Blanch, ; Marino et al., ) and wild (Honma & Chiba, ; Mugridge & Stallybrass, ; Paperna & Por, ) populations. G. maxillaris has a biphasic life cycle: a reproductive stage as free‐living adults (usually benthic) and an ectoparasitic larval stage.…”