Mosquitofish (Gambusia affinis) are a species of small fish commonly found in many different freshwater environments throughout Texas. However, the ecology of these environments varies as each habitat is unique with differing communities. Parasites are often overlooked in these environments and can lend clues to ecological relationships between organisms within the parasite’s life cycle. This study will examine the parasites within the internal organs and eyes of female mosquitofish obtained from three different freshwater lakes throughout Texas and compare the parasitic species found in each location. From the data collected we can learn more about organismal interactions in these environments

Gonzales, Stephen

Negovetich, Nicholas

Angelo State University Digital Repository

                  Figure 2. Locations throughout Texas from which the mosquitofish were gathered. Discussion           The data gathered from this research has yielded some interesting results. The most common parasite found was the digenetic trematode Posthodiplostomum minimum. (Fig. 4B). This species utilizes fish as the second intermediate host. The parasite is an economic concern, especially for fishermen, because they infect sport fishes and can decrease host survivability. They also have a very generalist life cycle and can infect many different hosts of  fish, which is why they could be found fairly easily in the mosquitofish4. Further examination of  mosquitofish in freshwater lakes could provide an indicator of  the prevalence of  P. minimum in areas popular for sport fishing because they are easier to obtain in greater numbers than larger fish.              Diplostomum sp. (Fig. 4A) parasites appear very similar to Posthodiplostomum minimum, but Diplostomum sp. are unencysted unlike P. minimum. Diplosotmum sp. are also known for infecting the eyes of  their intermediate fish hosts. The eye provides an advantage to the parasite because there is little to no competition with other species, which allows relatively heavy infections in this small area. Moreover, the parasite may hinder vision, thus making them more susceptible to predation by piscivorous birds, which are the definitive hosts2.            The Clinostomum sp. found only in fish collected from Mary’s Creek  (Fig. 3A-C) were all very interesting specimens. These parasites are also digenetic trematodes. The genera of  parasites are known as “yellow grubs” as they appear yellow in the metacercarial stage of  the intermediate fish host. They emerge from the snail host, often Helisoma sp., and penetrate the fish in the cercaria stage. From here they transition into the metacercaria stage and become the “yellow grub”1. Notably, the Clinostomum sp. from Mary’s Creek were white in appearance and encysted within the body cavity instead of  in the muscle.            A few encysted nematode larvae were recovered from these fish. Contracaecum sp. (Fig. 4C) is the largest of  the two species and exhibits an anteriorly directed appendix. These stomach worms utilize piscivorous birds, fish, and mammals as the definitive host6. Notably, this parasite is related to the nematodes that cause Anisakiasis in humans. The infection is acquired by eating raw or undercooked fish that possess the 3rd stage larvae. The second larval species, Spiroxys sp., is a small, red worm found in the mesenteries. It was identified by its characteristic head (Fig. 4D)3. Fish, the 2nd intermediate host, acquire this parasite by consuming infected crustaceans. The definitive host is a turtle. Eustrongylides sp. (Fig. 5A) are large nematodes located within the body cavity of  the fish. They are a common cause of  disease for many birds and fish and are zoonotic, meaning that they can be transferred to human hosts7.             Several parasites were uncommon. Neochinorhynchous sp. (Fig. 5C), an acanthocephalan, was only found in mosquitofish gathered from Big Oak River Ranch. The armed proboscis aids in attachment to the gut mucosa. Sebekia sp. found from Sunset Pond is a pentastome (Arthropoda) and is characterized by 4 hooks surrounding its mouth (Fig. 5B). Phyllodistomum sp. are typically common trematode species, however they appear to be uncommon in the Devil’s River at Big Oak River Ranch (Fig. 3D). This finding was unusual in that these parasites are typically found in the swim bladders of  their hosts8. However, these were all found free within the body cavity. The Protocephalus sp. is a tapeworm found within the intestines of  the mosquitofish. These are characterized by the suckers on the scolex. Two were found within this sample, however one had it’s scolex missing and was located in the body cavity rather than the intestines. The other had its suckers securely attached to the intestinal tissue, so out of  fear of  damaging the scolex not all of  the tissue was removed. The Analysis of  Internal Parasites in Mosquitofish Throughout Texas Jake Gonzales and Dr. Nicholas J. Negovetich Department of  Biology Introduction           Western mosquitofish (Gambusia affinis) are small freshwater fish that are common in North America and received their name from the mosquito larvae that form part of  their diet. These fish exhibit sexual dimorphism: females are typically 6-7 cm in length, and males are usually about 4 cm in length. Other than size difference, sex is detected by the presence of  a gonopodium, which is an anal fin that aids in sperm transfer during mating. Although native to North America, these fish have been introduced all over the world as a means to control mosquito populations in areas where mosquito-borne diseases such as malaria are a risk to the human population5. Because of  this and their ability to survive in a range of  aquatic habitats, G. affinis has been considered an invasive species in many parts of  the world.            Mosquitofish play an important role in aquatic systems by being both a predator and prey item. Thus, they have the potential to interact across the various trophic levels. An often under-studied aspect of  these interactions is the parasitic species that infect these fish. The complex life cycles of  parasites span multiple trophic levels and the presence of  parasites can reveal important information regarding the dynamic interplay between abiotic and biotic factors of  a habitat.  Methods and Materials           The mosquitofish specimens used for this research were acquired by a graduate student at my university from several locations throughout Texas. The specific locations used for this research were Mary’s Creek in Fort Worth, Texas; the Devils river running through the Big Oak River Ranch in Val Verde County, Texas; and Sunset Pond in San Angelo, Texas. Only female fish were examined to avoid observing differences in the parasite community because of  the sex of  the host.            Prior to necropsy, total length was recorded by measuring from caudal to the cephalic ends. The fish was then examined for black spots and other external parasites. Following this, the operculum was removed to reveal the gills, and each gill was excised individually for further investigation to identify the presence of  monogenean species. The internal organs were then extracted carefully and placed in a glass dish. The now empty body cavity was examined for any parasites within the peritoneal cavity or any encysted organisms living in the parietal peritoneum. The internal organs were then searched  extensively for embedded parasites within them. Finally, the eyes were removed and opened.            Any parasites located in the body cavity, internal organs, and eyes were then placed into a storage container filled with 70% ethanol solution for further staining, mounting, and identification procedures. However, nematodes were fixed in Glacial Acetic Acid prior to being stored in the 70% ethanol. Results         Figure 1. Summarized data of  the results found using prevalence and mean intensity References 1. Department of  Inland Fisheries & Wildlife. (2000, September). Yellow Grub (Clinostomum complanatum).            Retrieved April 4, 2016, from Department of  Inland Fisheries & Wildlife:           http://www.maine.gov/ifw/fishing/health/vol2issue6.htm 2. Desilets, H. D., Locke, S. A., McLaughlin, J. D., & Marcogliese, D. J. (2013). Community structure of  Diplostomum             spp. (Digenea: Diplostomidae) in eyes of  fish: Main determinants and potential interspecific             interactions. International Journal of  Parasitology 43: 929-939. 3. Hedrick, L. R. (1935). The life history and morphology of  Spiroxys contortus (Rudolphi); Nematoda:             Spiruridae. Transactions of  the American Microscopical Society 54: 307-355. 4. Lane, B., Spier, T., Wiederholt, J., & Meagher, S. (2015). Host specificity of  a parasitic fluke: is             Posthodiplostomum minimum a centrarchid-infecting generalist or specialist? Journal of  Parasitology 101: 6-17. 5. Masterson, J. (2008). Gambusia affinis (mosquitofish). Retrieved April 4, 2016, from Smithsonian Marine Station at Fort            Pierce: http://www.sms.si.edu/irlspec/Gambusia_affinis.htm 6. Nagasawa, K. (2012). The biology of  Contracaecum osculatum sensu lato and C. osculatum A (Nematoda:             Anisakidae) in Japanese waters: a review. Biosphere Science 51: 61-69. 7. Spalding, M. G., & Forrester, D. J. (1993). Pathogenesis of  Eustrongylides ignotus (Nematoda: Dioctophyma) in              Ciconiiformes. Wildlife Disease Association , 250-260. 8. Wa-Ho, H., Bray, R. A., Cutmore, S. C., et al. (2014). Two new species of  Phyllodistomum Braun, 1899 (Trematoda:              Gorgoderidae Looss, 1899) from Great Barrier Reef  fishes. Zootaxa , 551-562.                  Figure 3. The larval Trematodes recovered from the mosquitofish. (A) Acetocarmine stained Clinostomum sp. (B) Unencysted Clinostomum sp. (C) Unencysted Clinostomum sp. among encysted Clinostomum sp. (D) Metacercarial Phyllodistomum sp.                 Figure 4. Larval parasites recovered from the mosquitofish. (A) Trichrome stained metacercaria of  Diplostomum sp. (B) Trichrome stained metacercaria of  Posthodiplostomum minimum. (C) Anterior region of  the nematode Contracaecum sp. (D) Anterior region of  the nematode Spiroxys sp. Objective •  Document the internal parasites of  mosquitofish from 3 locations in Texas. C B A D Conclusion •  Mosquitofish play a crucial role as an important intermediate host in the life cycles of  many freshwater parasites •  Utilizing the presence of  parasites in mosquitofish can act as a useful tool in describing the ecology of  that environment Acknowledgements I would like to thank my research advisor Dr. Nicholas J. Negovetich for mentoring me and assisting me every step of  the way throughout this research. I would also like to thank Angelo State University Biology Department and the Angelo State University Honors Program for allowing me to conduct and present my research.  A B C D                    Figure 5. Larval parasites recovered from the mosquitofish. (A)  Anterior region of  Eustrongylides sp. Arrow pointing to nerve ring. (B) Scolex of  Sebekia sp. (C) Proboscis of  Neochinorhynchus sp. (D) Scolex of  Proteochephalus sp. Arrow pointing to suckers. A B C D Phylum Species Prevalence1(%) Mean1Intensity Prevalence1(%) Mean1Intensity Prevalence1(%) Mean1Intensity Prevalence(%) Mean1IntensityPlatyhelmenthis Diplostomum*sp. 20 3.25 7.02 3.25P.*minimum 75 4.2 11.8 3 40 4.6 43.9 4.24Clinostomum*sp. 23.5 2.25 7.02 2.25Phyllodistomum*sp 5 3 1.75 3Proteocephalus*sp. 5 2 1.75 2Nematoda Contracaecum*sp. 40 1 5 1 8.77 1Spiroxys1sp.* 25 5.6 8.77 5.6Eustrongylides*sp. 5 2 1.75 2Acanthochephala Neoechinorhynchus*sp. 5 2 1.75 2Arthropoda Sebekia*sp. 5 1 1.75 1Big1Oak1River1Ranch Mary's1Creek,1Fort1Worth Sunset1Pond,1San1Angelo Overall

The Analysis of Internal Parasites in Mosquitofish Throughout Texas

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The Analysis of Internal Parasites in Mosquitofish Throughout Texas

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