Behaviour, histopathology and immunobiology: interactions between the ectoparasite Neobenedenia (Monogenea: Capsalidae) and its host, Lates calcarifer (Perciformes: Latidae)

Trujillo González, Alejandro (2015) Behaviour, histopathology and immunobiology: interactions between the ectoparasite Neobenedenia (Monogenea: Capsalidae) and its host, Lates calcarifer (Perciformes: Latidae). Masters (Research) thesis, James Cook University.

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Capsalid monogeneans are harmful skin ectoparasites of ornamental and farmed fishes in tropical and subtropical marine environments. Within this group, Neobenedenia includes of particularly virulent species that exhibit low host specificity, a direct life cycle, high fecundity, environmentally resilient eggs, and have been associated with mass mortalities in aquaculture. There is a paucity of information on the interaction between Neobenedenia spp. and their fish hosts. Examination of Neobenedenia spp. infection and invasion behaviour, associated pathology and the effect on host immune responses can enable a deeper understanding of the potential impact of parasites on fish health and the complexity of parasite-host interactions. This study examined the interaction between Neobenedenia sp. and barramundi, Lates calcarifer, an important finfish species in commercial fisheries and aquaculture.

Neobenedenia spp. are cryptic in nature, which makes infection success and invasion routes challenging to elucidate. Larval recruitment and microhabitat preference was examined through time (Chapter 2) by using Neobenedenia sp. oncomiracidia (larvae) labelled with a fluorescent marker. Parasites were tracked on the body surface of the host with an epifluorescence stereomicroscope at 10 time intervals post exposure (15, 30, 60, 120 min, 24, 48 h, four, eight, 12, and 16 days). Parasites retained the fluorescent signal throughout the experiment. Neobenedenia sp. larvae settled opportunistically on the fish and then migrated to preferred microhabitats. Once recruitment had ceased (48 h), preferred microhabitats included the eyes, fins, and dorsal and ventral extremities on the main body. Reproduction could be an important factor for Neobenedenia sp. distribution, indicated by parasites aggregating on the fins within 24 h of attaining sexual maturity. Interestingly, some parasites attached beneath the scales of host fish, which may enable the parasite to be almost entirely secluded from the environment and could reduce the efficiency of current parasite management methods (e.g. chemical and freshwater bathing) in aquaculture.

High infection intensities of Neobenedenia species are well-known to cause pathology, however, the damage associated with mechanical attachment of the main attachment organ, the haptor, has not been examined. The pathology associated with haptor attachment of Neobenedenia sp. to L. calcarifer was examined through prepared histopathology sections at the haptor-host interface (Chapter 3). Fish were infected with Neobenedenia sp., and skin samples with attached parasites were collected from the eyes, mandible, operculum, middle body, ventral body and caudal fins 20 days post-infection. Histological slides were prepared by embedding, sectioning and staining tissue samples from the site of parasite attachment to the skin of host fish. Epithelial thickness and mucous cell abundance were measured in samples from uninfected and infected fish. Infected fish had lower mucous cell abundance, and the middle and ventral body surfaces had thinner epidermis compared to uninfected fish. Infected fish presented signs of dermal inflammation, epithelial loss, loss of intraepithelial attachment, and vacuolated epidermis compared to uninfected (control) fish.

The antibody response and acquired resistance of L. calcarifer to Neobenedenia sp. infections was examined following consecutive experimental infections (Chapter 4). Twenty fish were infected with Neobenedenia sp. oncomiracidia for 10 days with recovery periods (two weeks) between four consecutive exposure events. Before and after each exposure event, each fish was weighed, measured, and blood and mucous samples were collected for ELISA. After each infection the parasites were collected from each fish to analyse infection success, parasite size and reproductive status. Results showed that infected fish had significantly lower feed conversion efficiency than uninfected fish, parasites were significantly smaller on previously exposed fish and Neobenedenia infection success was significantly lower following three exposure events. There was no difference in infection success between the first, second and fourth exposure events. No differences in blood and mucous IgM levels between uninfected and infected fish could be detected by ELISA.

This thesis provided an innovative and rigorous approach to standard scientific methodologies to gain new information on the interactions between harmful monogenean parasites and host fish. Fluorescent labelling enabled rapid assessment of infection success and invasion routes of Neobenedenia sp. and revealed intriguing parasite behaviours that could aid parasite survival and reproductive success. Careful precision with histopathology at the haptor-host interface showed morphological differences on the epithelium of L. calcarifer when infected with Neobenedenia sp.. Nevertheless, parasite attachment did not stimulate an immune response to consecutive infections.

Item ID: 43749
Item Type: Thesis (Masters (Research))
Keywords: Asian sea bass; barramundi; behavior; behaviour; capsalid monogeneans; ectoparasites; histopathology; host-parasite interactions; host-parasite relationships; immunobiology; immunology; Lates calcarifer; Neobenedenia; parasitic flatworms; worm infections
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Trujillo González, Alejandro, Constantinoiu, Constantin C., Rowe, Richard, and Hutson, Kate S. (2015) Tracking transparent monogenean parasites on fish from infection to maturity. International Journal for Parasitology: Parasites and Wildlife, 4 (3). pp. 316-322.

Chapter 3: Trujillo-González, A., Johnson, L.K., Constantinoiu, C.C., and Hutson, K.S. (2014) Histopathology associated with haptor attachment of the ectoparasitic monogenean Neobenedenia sp. (Capsalidae) to barramundi, Lates calcarifer (Bloch). Journal of Fish Diseases. pp. 1-5.

Date Deposited: 18 May 2016 23:29
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070401 Aquaculture @ 33%
07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070404 Fish Pests and Diseases @ 33%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060307 Host-Parasite Interactions @ 34%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830102 Aquaculture Fin Fish (excl. Tuna) @ 50%
96 ENVIRONMENT > 9604 Control of Pests, Diseases and Exotic Species > 960407 Control of Pests, Diseases and Exotic Species in Marine Environments @ 50%
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