Treatment of gyrodactylid infections in fish

Abstract

Since Norway experienced the devastating Gyrodactylus salaris (Monogenea) epidemics in Atlantic salmon Salmo salar, there has been heightened interest in how to treat gyrodactylosis in fish. Here we summarize chemical treatments previously used against gyrodactylids and discuss the main problems associated with these control measures including efficacy, host toxicity, human health concerns and application of treatments. Unfortunately, for these reasons and because of the different methodologies and different parasite and host species used in previous studies, it is difficult to recommend effective chemotherapeutic treatments. However, we suggest a method for manual removal of gyrodactylids from the host suitable for use in small-scale research facilities. KEY WORDS: Gyrodactylus · Control treatment · Efficacy · Toxicity Resale or republication not permitted without written consent of the publisherDis Aquat Org 86: [65][66][67][68][69][70][71][72][73][74][75] 2009 peared promising in laboratory studies (Soleng et al. 1999, 2005, Poléo et al. 2004, field trials in Norway using aluminium in combination with rotenone have been problematic because successful treatment of the whole river system requires maintaining a specific concentration without exceeding levels toxic to Atlantic salmon (P. Shave pers. comm.). Aluminium toxicity to fish increases under acidic water conditions (Birchall et al. 1989, Poléo 1995, Soleng et al. 1999, and elevated environmental aluminium levels can result in Alzheimer's disease (Doll 1993) and decreased agricultural and forestry productivity (Bi et al. 2001). Organophosphates, such as trichlorfon, are no longer in use against fish parasites as they cause irreversible effects in nontarget species by phosphorylating acetylcholinesterase (see Kozlovskaya & Mayer 1984, Peña-Llopis et al. 2003, Costa 2006. Acute and chronic toxicity to other aquatic organisms has also been reported for benzimidazoles (e.g. Oh et al. 2006); however, due to their low efficacy (see Appendix 1), these are not preferred over broad antiparasitic treatments such as formalin.In addition to efficacy, environmental and human health issues, the main problem associated with current gyrodactylid treatments is their toxicity to the host (Schmahl & Taraschewski 1987, Santamarina et al. 1991, Tojo et al. 1992, Scholz 1999, Ekanem et al. 2004, Srivastava et al. 2004. Even widely used compounds, such as formaldehyde, may significantly change the host's gill structure and epidermis (Speare et al. 1997, Sanchez et al. 1998, Buchmann et al. 2004). For instance, although zinc exposure initially stimulates host mucus production, mucus is subsequently depleted leaving the fish more susceptible to microbial infections (McGeer et al. 2000). If these fish are subsequently used for experimental infections without a sufficient recovery period, they may show an abnormal response to infection (see review by Bakke et al. 2007). Host respiratory problems are also a common side effect of gyrodactylid treatments due to dire...

Efficacy of commercially available products against Gyrodactylus turnbulli infections on guppies Poecilia reticulata

“…Water and the anti-helminthic levamisole (Levacide) were used as negative and positive controls. Both Melafix ® and Pimafix ® were tested at the concentrations recommended by the manufacturer (see Table 1), the individual and combination treatments were administered to reflect the concentration in the products and levamisole was used at the known effective concentration of 1 ml l −1 (Schelkle et al 2009(Schelkle et al , 2015.…”

“…Screening for parasites before (Day 1) and after treatment (Day 8) followed the protocol of Schelkle et al (2009), whereby fish were lightly anaesthetized with 0.02% MS222 before their parasites were counted using a dissection microscope and optic fibre illumination. Fish with a parasite load of between 3 and 200 parasites were isolated and individually maintained in 1 l pots for the duration of the experiment, receiving daily water changes followed by treatment applications at the same concentrations as in vitro (see Table 1).…”

“…Gyrodactylids are ectoparasitic helminths that are ubiquitous on teleost fish and the cause of considerable economic damage in infected fish populations (Bakke et al 2007). There is no 100% effective treatment available against gyrodactylids (Schelkle et al 2009, 2010, 2013, Bowker et al 2012; a model system using Gyrodactylus turnbulli infecting guppies (Poecilia reticulata) under controlled conditions was employed to test commercial products alongside gas chromatography-mass spectrometry to identify and measure the relative abundance of individual compounds in cajuput and West Indian bay essential oils.…”

Parasites pitched against nature: Pitch Lake water protects guppies (Poecilia reticulata) from microbial and gyrodactylid infections

“…Fish were screened for external parasites using a fibreoptic light and a stereo-microscope according to the methods described by Schelkle et al (2009). Fish were maintained individually in 1L pots throughout the duration of the experiment and were fed on Aquarian ® fish flakes once daily.…”

The effect of Yucca schidigera liquid extract on water quality and survival of Pacific Red Snapper Lutjanus peru during acclimatization

“…However, more research is still needed to determine the effectiveness of particular substances in each species and its real potential negative effects. This process involves experimenting with different chemicals and techniques to find out the most effective method to minimize the stress (Schelkle et al 2009). Additionally, it is necessary to determine the optimum dose of substance since it may vary depending on the water quality and the severity of the pathogen being treated.…”