Histopathology Associated with Haptor Attachment of the Ectoparasitic Monogenean Neobenedenia Sp
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Journal of Fish Diseases 2014 doi:10.1111/jfd.12320 Short Communication Histopathology associated with haptor attachment of the ectoparasitic monogenean Neobenedenia sp. (Capsalidae) to barramundi, Lates calcarifer (Bloch) A Trujillo-Gonzalez 1, L K Johnson2, C C Constantinoiu2 and K S Hutson1 1 James Cook University, Centre for Sustainable Tropical Fisheries and Aquaculture, College of Marine and Envir- onmental Sciences, Townsville, Qld, Australia 2 James Cook University, Centre for Biosecurity in Tropical Infectious Diseases, College of Public Health, Medical & Vet Sciences, Townsville, Qld, Australia Keywords: Asian sea bass, epidermis, mucous cells, organs lack accessory chitinous structures and are pathology, skin fluke, teleost. located directly above the pharynx, which is used to graze on epidermal and mucous cells of the fish Capsalid monogeneans are harmful ectoparasites (Whittington 2012). of ornamental and farmed fishes in tropical/sub- The strong adhesion of the haptor, mechanical tropical marine environments (Thoney & Hargis attachment of the hamuli and sclerites (Ogawa 1991; Hirazawa et al. 2011; Whittington 2012). et al. 2006), as well as the adhesion of the ante- Neobenedenia spp. have low host specificity, a rior attachment organs when grazing, can damage direct life cycle, high fecundity and robust eggs, the host’s epidermis (Kaneko et al. 1988; Ogawa which contribute to their ability to inflict mass et al. 2006; Hirazawa et al. 2010), increasing the mortalities in aquaculture (Ogawa et al. 1995; likelihood of secondary infections (Thoney & Deveney, Chisholm & Whittington 2001; Hargis 1991; Leong & Colorni 2002). Lesion- Ruckert,€ Palm & Klimpel 2008; Whittington level histopathology sections that exhibit the hap- 2012). tor–host interface are rare and examinations of the Neobenedenia spp. attach to external surfaces of change in epidermal morphology associated with their host using two attachment organs located infected fish are limited. In this study, we exam- anteriorly and one larger posterior attachment ined epidermal damage associated with the site of organ called the haptor. The haptor is believed to haptor attachment in six separate regions of act as the principal anchoring organ of the para- farmed barramundi. Characteristics evaluated in site to the host (Whittington 2012). This organ Neobenedenia sp.-infected fish included changes in has chitinous structures that provide mechanical epidermal thickness and in the number of mucous attachment including paired anterior hamuli, cells compared with similar areas in uninfected accessory sclerites, posterior hamuli and peripheral controls. hooklets (Whittington & Horton 1996). A mar- Forty hatchery reared freshwater L. calcarifer Æ ginal valve on the haptor allows the organ to cre- (mean 125 25 LT mm) were acclimated to sea ate suction on the host. The anterior attachment water for 24 h prior to 20 fish each being infected with 20 Neobenedenia sp. oncomiracidia each (see Correspondence A Trujillo-Gonzalez, Marine Parasitology Lab- Hutson et al. 2012; James Cook University ethics oratory, Centre for Sustainable Tropical Fisheries and Aquacul- approval no. A1857). The remaining 20 fish were ture and the School of Marine and Tropical Biology, James Cook University, Townsville, Qld 4811, Australia not infected. The Neobenedenia sp. used in this (e-mail: [email protected]) study is presently unidentified given the absence Ó 2014 John Wiley & Sons Ltd 1 Journal of Fish Diseases 2014 A Trujillo-Gonzalez et al. Epithelial histopathology of diagnostic criteria to differentiate between geo- apical layer and mucous cells were counted in four graphical/host isolates and species (Whittington selected microscopic fields along the epidermal 2004, 2012). Parasites were accessioned in the layer in each tissue sample at 4009 magnification. Australian Helminth Collection (AHC), South In the case of infected fish, microscopic fields were Australian Museum Australia (SAMA: AHC selected within the haptor–host interface and hap- 35461). Twenty-one days post-infection all 40 fish hazardly on epidermis adjacent to the haptor (inter- were killed with an overdose of Aqui-S aquatic nal control). Statistical analysis was performed â anaesthetic in sea water, which did not kill para- using S-plus 8 from Spotfire . One-way ANOVAs sites or cause them to detach from the host (see were used to analyse differences in epidermal mor- Sharp et al. 2004). Each fish was then immersed phology between uninfected and infected fish À in a shallow tray containing sea water (35 g L 1), within each region. Differences between pairs of and tissue samples bearing an individual live para- means were determined using a Tukey’s HSD test. site were collected from infected fish using a surgi- A chi-squared contingency test was used to examine cal scalpel blade. Tissue samples were collected differences in the number of mucous cells. Signifi- from the mandible, operculum, middle body, ven- cance was accepted at P < 0.05. tral body and caudal fins. Samples were approxi- The haptor of Neobenedenia sp. caused direct mately 1 cm2 and consistently collected from mechanical damage to the fish epidermis and trig- equivalent locations within regions on uninfected gered epidermal morphological changes. Dermal and infected fishes. Eyes were collected whole. inflammation (Fig. 1d) and epidermal loss (Fig. 1c, Samples were fixed in 1% Bouin’s solution for d) were observed in the majority of infected regions 48 h prior to being routinely processed, paraffin but was absent in uninfected controls (Fig. 1a,b). embedded, and 4 lm sections stained with hae- The marginal valve of the haptor caused mechanical matoxylin and eosin (Gibson-Kueh et al. 2012). compression of the epidermis (Fig. 2a,b,d) and Sections were made so that the interface between may have contributed to detachment of the basal the haptor and the host body surface could be layer (Fig. 2c). Accessory sclerites ruptured the epi- observed by light microscopy. Some parasites dermal layer (Fig. 2b, inset). Rarely, was the haptor detached during the fixation and embedding pro- directly associated with haemorrhage or epidermal cess, which limited the total number of samples inflammation (Figs 1d & 2d, inset), and there was available for analysis (Table 1). Parasites detached no evidence of ulceration in infected fish. from all eye preparations and were not included Infected fish had significantly lower mucous cell in the analyses. counts in all regions compared with uninfected Epidermal thickness and the number of mucous fish (P < 0.001, Fig. 3a). Infected fish exhibited a cells were quantified beneath the haptor, the epi- trend for lower epidermal thickness in all regions dermis adjacent to the haptor (internal control) compared with uninfected controls (Fig. 3b), which and on equivalent epidermis from uninfected fish is congruent with previous studies (Hirayama, Kaw- (Table 1). Epidermal thickness was measured ano & Hirazawa 2009). Internal controls indicated from the basal epithelial layer to the external or that morphological changes were not limited to areas under the haptor, although the greatest impact Table 1 Total number of sections examined for histopathol- was quantified at the site of haptor attachment ogy, epithelial thickness and mucous cell counts for each (Fig. 3). This surrounding damage could be a con- region sequence of the feeding activity of the parasite. Neo- benedenia spp. may use the haptor as a fixed No. skin sections Region Condition No. fish examined rotation point using the anterior attachment organs to aid feeding within the radius of the total body Mandible Uninfected 6 6 length. Furthermore, movement of capsalid mono- Infected 4 5 Operculum Uninfected 4 5 geneans over the body surface of the host may also Infected 6 6 account for the observed surrounding damage Middle body Uninfected 7 8 (Whittington & Ernst 2002; Ogawa et al. 2006). Infected 5 5 Ventral body Uninfected 5 5 Neobenedenia spp. are believed to migrate following Infected 6 6 initial recruitment on the host (Ogawa et al. 2006; Caudal fin Uninfected 2 2 Hirayama et al. 2009; Hirazawa et al. 2011); how- Infected 6 6 ever, it is challenging to track migrations through Ó 2014 John Wiley & Sons Ltd 2 Journal of Fish Diseases 2014 A Trujillo-Gonzalez et al. Epithelial histopathology (a) (b) mc mc e e d s s (c)e (d) h ( h as d N ( s m e s Figure 1 Histopathology of the ventral body surface in uninfected (a,b) and infected Lates calcarifer with Neobenedenia sp. (c,d). Uninfected fish had numerous mucous cells in the epidermis (a,b). The parasite’s haptor compressed the epidermal layer of the host (c, brackets). Infected fish presented thinner epidermis and mucous cells were rare at the haptor–host interface (c,d). N = Neobenede- nia;as= accessory sclerites; d = dermis; e = stratified squamous epithelial cells; h = haptor; m = marginal valve; mc = mucous cells; and s = scale. Morphological terms follow Whittington & Horton (1996) and epidermal morphology follows Takashima & Hibiya (1995). (H&E stain, a, c = 9200; b, c = 9400), scale bars = 100 lm. (a) (b) N N h m m e h d a s fr (c) (d) h as e N h d m s bd e hm Figure 2 Histopathology associated with haptor attachment of Neobenedenia sp. to Lates calcarifer on the middle body (a,d), caudal fin (b) and ventral body surface (c) of infected fish. Epithelial loss was observed in the majority of samples at the haptor–host inter- face (AD). Accessory sclerites caused epidermal damage (b, b inset, c) and the marginal valve compressed the epidermis of the host (a, b, d). N = Neobenedenia;as= accessory sclerite; bd = epithelial basal layer (detached); d = dermis; e = stratified squamous epi- thelial cells; fr = fin ray; h = haptor; hm = haemorrhage; m = marginal valve; and s = scale. Parasite terminology follows Whitting- ton & Horton (1996) and epidermal morphology follows Takashima & Hibiya (1995). (H&E stain, 9100, insets = 9400), scale bars = 100 lm. Ó 2014 John Wiley & Sons Ltd 3 Journal of Fish Diseases 2014 A Trujillo-Gonzalez et al.