A review of Dendromonocotyle (Monogenea: Monocotylidae) from the skin of stingrays and their control in public aquaria

Abstract

Abstract. Dendromonocotyle species (Monogenea: Monocotylidae) are the only monocotylids to parasitize the skin of chondrichthyan hosts. Currently 11 species are recorded from the skin of ray species in the Dasyatidae, Myliobatidae and Urolophidae. There have been increasing reports of Dendromonocotyle outbreaks on rays kept in public aquaria. This paper provides a broad review of Dendromonocotyle that should assist taxonomists and aquarists with species identification and help decisions on potential control methods for Dendromonocotyle infections. The taxonomy and host-specificity of Dendromonocotyle are discussed and a key to current species is provided. We summarise what little is known about the biology of Dendromonocotyle including egg embryonation and hatching, feeding, camouflage and reproduction. The efficacy of freshwater baths, chemical treatments and biological control measures such as the use of cleaner fish for Dendromonocotyle is also discussed. We demonstrate that effective control of Dendromonocotyle on captive rays is hampered by the lack of basic biological data on the life cycle of the parasites. A case history is provided outlining the success of a public aquarium (Underwater World, Mooloolaba, Queensland, Australia) in managing D. pipinna infections on captive Taeniura meyeni without chemical intervention simply by taking measures to reduce host stress.Most Monogenea are recorded from the skin, fins and gills of teleost fish and only about 200 valid monogenean species in seven families (Acanthocotylidae, Amphibdellidae, Capsalidae, Hexabothriidae, Loimoidae, Microbothriidae, Monocotylidae) are known from various sites on chondrichthyans (Whittington and Chisholm 2003). In our experience, the infection intensity of monogeneans on wild sharks and rays is generally low. However, when elasmobranchs are kept in captivity, monogenean intensities can increase significantly due to their direct life cycle. In extreme cases, monogeneans can cause lesions at their attachment site which may result in the death of the elasmobranch either indirectly (via secondary infections) or directly (e.g. Poynton et al. 1997, Bullard et al. 2001.The Monocotylidae comprises 23 genera and represents approximately 60% of all monogeneans recorded from elasmobranchs . This is a unique family because members can parasitize a broad diversity of sites on their chondrichthyan hosts including the skin, gills, nasal tissue, urogenital system and inner wall of the body cavity. Members of Dendromonocotyle are the only monocotylids to parasitize the skin. Recently there have been an increasing number of reports of Dendromonocotyle outbreaks on rays in public aquaria.This review provides information on the taxonomy of Dendromonocotyle and a key to species to assist with identification. We highlight how little is known about the biology of Dendromonocotyle and how this lack of information impacts on the development of effective biological and chemical control measures. We then outline how one public aquarium, Underwater World, in Que...

Heterocotyle tokoloshei sp. nov. (Monogenea, Monocotylidae) from the gills of Dasyatis brevicaudata (Dasyatidae) kept in captivity at Two Oceans Aquarium, Cape Town, South Africa: Description and notes on treatment

“…Until now, oral application at this dosage in elasmobranchs has not been investigated. Janse and Borgsteede (2003) presented results of both a bath treatment and oral application of praziquantel to treat captive spotted eagle rays Aetobatus narinari (Euphrasen, 1790) infected with monocotylids they misidentified as Clemacotyle australis Young, 1967 (likely Dendromonocotyle torosa Chisholm et Whittington, 2004;see Whittington and Chisholm 2008) and an unidentified hexabothriid species. Orally administered praziquantel at 10-40 mg/kg (note the exact concentrations are difficult to interpret from their results) did not remove the parasites infecting A. narinari, but limited shortterm success was achieved with bath treatments.…”

“…Monocotylid monogeneans are known to cause health problems in stingrays maintained in public aquaria (Chisholm and Whittington 2002, Janse and Borgsteede 2003, Chisholm et al 2004, Vaughan et al 2008a, Vaughan and Chisholm 2009). Monocotylids parasitising the skin surface of stingrays held in captivity have received the most attention because infections are more visible and physical damage associated with feeding worms typically presents itself as conspicuous tissue discolouration.…”

Three Dendromonocotyle species (Monogenea: Monocotylidae) reported from captive rays, including D. lotteri sp. n. from Himantura gerrardi (Elasmobranchii: Dasyatidae) in the public aquarium at the Atlantis resort, Dubai

“…This is the fi rst record of D. kuhlii from a public aquarium. Chisholm et al (2004) found that a proactive approach to their management, by reducing host stress, supported a sustainable equilibrium between host and parasite. Identifying and reducing stressors is paramount, but not always possible.…”

“…There are currently 16 known species of Dendromonocotyle, of which 7 are reported from stingrays in captivity (see Chisholm and Whittington 1995, 2009, Chisholm et al 2001, 2004, Vaughan et al 2008. It has become clear that Dendromonocotyle infections can cause health problems in stingrays kept in public aquaria.…”

Dendromonocotyle urogymni sp. nov. (Monogenea, Monocotylidae) from Urogymnus asperrimus (Elasmobranchii, Dasyatidae) off eastern Australia

“…Members of Dendromonocotyle (Monogenea, Monocotylidae) parasitise the dorsal surface of stingrays and have been recorded from ray species in the Dasyatidae, Myliobatidae and Urolophidae (see Chisholm et al 2004). The porcupine ray, Urogymnus asperrimus (Bloch et Schneider, 1801) has a wide distribution throughout the Indian and Indo-West Pacific Oceans but is rarely collected in the coastal waters of Australia (Last and Stevens 1994, Theiss et al in press).…”