Health Impacts of Cymothoid Parasitic Isopods on Symphodus tinca and Boops boops Hosts in the Northwestern Mediterranean Sea at STARESO, Corsica, France Wade Dugdale, Kelsey Metzger Department of Ecology and Evolutionary Biology - University of California, Santa Cruz 2014 ABSTRACT: The present study is an attempt at understanding the relationship between cymothoid parasitic isopods and the body condition of their hosts. Three species of parasitic isopod including Anilocra physodes, Nerocila bivittata and Cymothoa oestroides as well as two species of host fish, Boops boops and Symphodus tinca, were collected for study. A standard length to body mass relationship was established for each host species by means of a linear regression analysis. From this, the means of mass residuals for both parasitized and non- parasitized fish were analyzed to reveal that S. tinca hosts suffered a significantly higher health detriment than B. boops hosts, who showed little to no change in weight. Furthermore, roaming fish surveys designed to estimate the relative abundance of parasitized individuals within each local population of host species were conducted along three specific transects. These surveys found varying abundances of parasitized fish according to host size and location. INTRODUCTION is known about the specific biology and life history of many cymothoid species (Smit et Cymothoids (Crustacea, Isopoda) are al., 2014). These parasites associate parasitic isopods inhabiting both marine and themselves with many commercially and freshwater systems. The cymothoid family is economically important fish around the among the largest of parasitic isopod world and could cause significant financial families and include at least 380 species loss to fisheries by stunting, damaging or total (Smit et al., 2014). They exist in all of even killing these fish (Samn et al., 2014). the world’s oceans excluding polar waters, With the recent growth of the sea-cage however the vast majority of cymothoid aquaculture practices, events of cymothoid species inhabit the tropical waters of the parasitism have been shown to significantly Central Indo-Pacific. Furthermore, 35 of affect cultured fish stock, and are all these species reside in the Northern Atlantic suspected to have been transmitted from Ocean and Mediterranean Sea, the research wild fish (Horton et al., 2001). A better location for this study (Smit et al., understanding of these parasites and the 2014). While cymothoids parasitize relationships with their hosts may help hundreds of species of fish worldwide, little Dugdale & Metzger | 2 mitigate losses incurred by parasitism in at STARESO research station in Calvi, aquaculture. Corsica? While cymothoid parasites may damage sea cage aquaculture,We hypothesize Hudson that et al.a.) suggestsIsopod parasites that, specialized parasites play a key role in ecosystem functioning and can be valuable in the promotion of biodiversity. Density-dependent transmission along with host specific parasites can link specialized parasites to a positive effect on biodiversity (Hudson et al., 2006). Parasites cause a negative health impact to their provide a means of natural population individual hosts. Comparisons between the control, however parasites do not only target relationships of body mass to standard fish species with potentially damaging length observed in non-parasitized and population sizes, they can threaten parasitized fish will be used to show the endangered species as well. health detriment (lower unit body mass per unit body length) caused by incidences of Cymothoids live mainly attached to the parasitism. exterior of the host fish on the skin or fins (Smit et al., 2014). They primarily settle on We hypothesize that b.) Incidences of the caudal fin, operculum, or sometimes in parasitism in S. tinca and B. boops will the mouth or gills of their host (Öktener and affect the hosts to differing degrees. The Trilles 2004). In this study three specific proportional weight loss experienced by species of Cymothoidae (a specific family of individuals of both species, as determined parasitic isopoda) were observed to settle in by the relationships of body mass to three different areas of the host fish and standard body length, will be compared to were associated with two specific host assess the degree to which parasites affect species. First, Anilocra physodes was their respective host species. observed to parasitize B. boops and was 2. To what degree do parasitic isopods affect local S. tinca and B. boops populations at STARESO, Calvi, Corsica? found generally attached to the caudal peduncle and gill covers. Second, Nerocila We hypothesize that incidences of bivittata is found on S. tinca most parasitism are not frequent enough to cause commonly on basal regions of the caudal significant detriment to the total population rays. Finally, Cymothoa oestroides also of S. tinca and B. boops. Fish population known as the “tongue eating parasite,” was surveys will examine the prevalence of found on a B. boops individual and is parasitized S. tinca and B. boops individuals exclusively confined to the mouth and gills within the total population of each species at of its host. STARESO. At STARESO Station de Recherches MATERIALS AND METHODS Sous Marines et Océanographiques in Calvi, Corsica, France, a number of S. tinca and B. Species Description boops individuals were observed to be Marine parasitic isopoda (Cymothoidae) carrying ectoparasitic isopods of various are likely a central and dominant group sizes and numbers. This study will of crustacean parasites in fish and have been investigate how these parasites affect the known to cause detrimental effects on fish health of the host fish and that of the entire health, growth, behavior, fertility and fish population by asking these questions: mortality. In this study three specific species 1. Do parasitic isopods affect the of cymothoidae are studied; Anilocra health of S. tinca and B. boops individuals physodes, Nerocila bivittata and Cymothoa Dugdale & Metzger | 3 oestroides, all three of which feed on the known to carry more than 300 eggs in her blood and tissue of their hosts (Öktener and marsupium during one reproductive cycle. Trilles 2004). Their appendages are highly In the present study, two different species specialized allowing them to securely hold of host were observed. Symphodus tinca, a the body of fish and efficiently tear the reef associated labrid species found on strong body muscles of host fish (Samn et rocky, algae covered reefs and seagrass al., 2014). Cymothoidae represent only one meadows, has been documented to host up of the five known families of cymothoid to 18 species of metazoan parasites (Campos isopoda and are exclusively parasitic on and Carbonell 1994). Boops boops on the marine and freshwater fishes (Samn et al., other hand is a demersal, semi-pelagic fish 2014). This specific family of cymothoid is species known to host about 67 different one of the most well known isopoda families species of metazoan parasites (Olmo et al., to date, having a large number of species 2007) and has been suspected in some cases discovered and described before 1950 (Smit to transmit C. oestroides to cultured sea et al., 2014). bream, Sparus auratus, and sea bass, Cymothoidae are protandrous Dicentrarchus labrax (Horton et al., 2001). hermaphrodites and, starting life as male, Site Description spend a short period of their pre-host lives as free swimming manca (a post-larval stage). All experiments and surveys were done in These young isopods have hatched in the Calvi, Corsica, France at STARESO marsupium of their mother and undergone research station in the months of September several moults (pullus l and pullus ll) until and October 2014. Fish specimens were they finally leave the brood pouch in search collected by spear while skin diving or on of a host (Smit et al., 2014). The SCUBA. All fish population surveys were undeveloped and sexually non-differentiated performed on SCUBA. isopods are extremely fit for swimming and can survive without a host for several days Surveys were conducted between 3 to 8 by feeding on yolk stores (Smit et al., 2014). meters of depth, along the interface between Once an individual has settled on a suitable coastal rocky reefs and vast Posidonia host it becomes sexually differentiated oceanica meadows, which dominate the (male) yet remain capable of leaving that ocean floor, leaving little sand exposed. host if necessary as long as they have not These coastal algae covered reef and cobble molted into the following pre-adult form. areas were central survey sites in this study, However, once an individual has reached an beginning at the water’s edge and extending appropriate size and found a host they down to the substrate and Posidonia transform to female and eventually lose their oceanica meadows. Several artificial reefs ability to swim (Smit et al., 2014). This may exist near STARESO, but only one was be why the three species mentioned above observed in our study; this artificial reef is a and examined in this study were more jetty made of concrete jacks located along commonly found in pairs on a single fish, the Northern exterior edge of the harbor. one (we believe the female) being much Impact of Parasites on Host Body Condition bigger than the other. Cymothoidae species reproduce all year and females have been Dugdale & Metzger | 4 In order to examine the impact of normalized them by the mass of each cymothoid parasites on their hosts, we parasitized individual. We then compared conducted collections on SCUBA to obtain these proportional residuals of mass for specimens of each host species for length parasitized individuals across each species and weight analysis. An initial power using a two tailed t-Test to determine if the analysis using JMP determined that at least parasites affected each host species in five parasitized individuals of each species significantly different ways (critical p-value: would be required to provide significant 0.05). results. After collection by spear, all Prevalence of Cymothoid Ectoparasitism in specimens were photographed, weighed Local Populations with a digital scale, and measured using ImageJ software.