Lernaea cyprinacea, Linnaeus, 1758

Welicky, Rachel L., Swardt, Jurgen De, Gerber, Ruan, Netherlands, Edward C. & Smit, Nico J., 2017, Drought-associated absence of alien invasive anchorworm, Lernaea cyprinacea (Copepoda: Lernaeidae), is related to changes in fish health, International Journal for Parasitology: Parasites and Wildlife 6 (3), pp. 430-438 : 434-436

4.1. Molecular con fi rmation of Lernaea cyprinacea

This study provides the first molecular data of the invasive copepod L. cyprinacea from South Africa and confirms the species identity as L. cyprinacea . Genetic comparisons of 18S rDNA sequences from the current study were compared to all the available 18S rDNA sequences from the GenBank database (see Table 1), including a sequence of L. cyprinacea [GenBank: DQ107556] from the type host, Cyprinus carpio from China (see Song et al., 2008; McAllister et al., 2015). Although L. cyprinacea has a cosmopolitan distribution, very limited molecular data from individuals in the native (including the type locality, Europe) and invasive ranges are available. Thus, the current study provides molecular data for future studies examining the confirmation, identification, and distribution of this parasite species across its type locality, native and invasive ranges.

4.2. Lernaea cyprinacea infection and Mozambique tilapia health and condition

This study is the first to evaluate the associations between drought condition, anchorworm infection, and the health of wild Mozambique tilapia, and the first to do so by examining the changes in health of a fish population that was subjected to a natural experimental parasite removal treatment associated with the current drought conditions. Drought can subject fish to a variety of abiotic and biotic stressors ( Magoulick and Kobza, 2003; Matthews and Marsh-Matthews, 2003; Crook et al., 2010), thereby negatively and indirectly influencing their health and condition. Parasitism can also negatively influence the health and condition of fish (e.g. Berry Jr. et al., 1991; Paperna, 1996; Barber et al., 2000). Generally, fish collected before drought were in reduced health despite inhabiting a more typical floodplain pan ecosystem, whereas those collected during drought were in better health despite living in a drought-effected system, where water quality and access to resources are greatly altered ( Lake, 2003; Balcombe et al., 2005). The most conspicuous difference between fish collected before and during drought, was that all fish collected before drought were infected with anchorworms, whereas all fish collected during drought were not infected with anchorworms. Thus it is likely that anchorworm infection contributed to the reduced health and condition of Mozambique tilapia.

Relative to uninfected fish, infected fish had reduced hepatosomatic condition yet higher gutted condition, and inhabited a more resource rich environment ( Carrasco et al., 2012; Dyer et al., 2013; Dube et al., 2017). Both hepatosomatic and gutted condition factors of fish are indicators of the quality and availability of their prey resources, as these organs both store energy. The rate at which energy is metabolized varies with respect to the organ and a hosts' infection status. Fish hosts more readily use energy from the liver than muscle ( de la Higuera et al., 1999; de la Higuera, 2001), and parasites may process host nutrients from different host tissues at different rates ( Demopoulos and Sikkel, 2015; Welicky et al., 2017, in press). Thus, the hepatosomatic and gutted condition results of this study are neither surprising nor contradictory. The reduced liver condition of infected fish likely reflects the short-term effects of infection, where hosts are metabolizing lipid and carbohydrate more readily than protein ( de la Higuera et al., 1999; de la Higuera, 2001). Declines in glycogen levels have been correlated with reduced liver size in previous studies ( Maes et al., 2005; Gerber et al., 2017), and Barber (2005) determined that copepod parasite infection reduced fish liver size. The higher gutted condition of infected fish likely reflects that changes in gutted condition with respect to parasite infection occur over a longer duration of time as compared to changes in hepatosomatic condition. Moreover, higher gutted condition of infected fish may reflect that prey resources were different, more readily available for hosts to intake, and/or easier to locate, if overall water quality and turbidity were better before drought as compared to during drought ( Semyalo et al., 2011; Dyer et al., 2013). Further analyses that account for the duration of anchorworm infection and regularly monitor changes in water quality would aid in a more complete understanding of temporal changes in host condition that are associated with drought and infection.

Since infected fish had reduced short-term energetic reserves, it is likely that they had less energy to allocate towards reproduction ( Hall et al., 2007; Heins et al., 2014). This may explain the reduced gonad condition of anchorworm-infected Mozambique tilapia that we observed. Reduced fecundity of fish in association with parasitism is well-documented (e.g. Lafferty and Kuris, 2009; Fogelman et al., 2009), and the fish gonad condition and associated correlation analyses conducted in this study support these previous findings. Nevertheless, Barson et al. (2008) did not find a correlation between L. cyprinacea intensity and Mozambique tilapia gonad condition in Zimbabwean river impoundments, despite having a similar sample size. These contrasting results may highlight the natural variability that occurs as a result of site and individual fish differences (e.g. Barber et al., 2000; Blanchet et al., 2010). In this study, the reduced gonad condition but higher gutted condition of infected fish compared to uninfected fish may demonstrate an energetic trade-off between growth and maintenance, and reproductive effort ( Tytler and Calow, 1985; Wootton, 1985; Mangel and Stamps, 2001).

Although our statistical analyses suggest uninfected fish had reduced spleen condition compared to infected fish, the recorded observations on spleen condition suggest this is not the case. All uninfected fish had spleens that were normal in size and not swollen, and some of the infected fish had spleens that were enlarged and swollen. Both smaller and larger spleens may be indicative of infection ( Adams et al., 1993; Kortet et al., 2003), and large spleens may be positively associated with a fish's immune response to infection, and overall reduced condition ( Kortet et al., 2003; Ottováet al., 2005; Lamkova ́et al., 2007). Our confounding spleen condition statistical analyses may suggest uninfected fish are also responding to infection, but this infection is likely not parasite related. The severity of this unknown infection may be less than that of anchorworm infection given that low haematocrit values are associated with disease ( Adams et al., 1993), and infected fish had lower haematocrit values than uninfected fish.

The overall HAI values indicated that infected fish were in significantly poorer health than uninfected conspecifics. There was also a positive correlation between HAI value and anchorworm intensity, but this result was not statistically significant. This may be an artefact of small sample size, as the majority of our observations provide support for this relationship. For example, compared to uninfected fish, the frequency and intensity of skin lesions and fin fraying was greater for infected fish. Moreover, the gills, liver, and spleen were discoloured in infected fish. Such aberrations are typical of anchorworm-infected fish (Berry Jr. et al., 1991; Avenant-Oldewage, 2012; Hangan et al., 2013). Interestingly, the haematocrit and blood plasma health assessment scores of uninfected fish were consistently greater or equal to that of infected fish. High haematocrit values and low plasma protein concentrations in fish are associated with dehydration and impaired water balance ( Wedemeyer and Yasutake, 1977; Novotny and Beeman, 1990). Although laboratory studies have demonstrated that short-term (hours to 1 month) exposure to hypersalinity does not influence the blood parameters of aquaculture reared tilapia ( Sardella et al., 2004; Kammerer et al., 2010), studies examining the chronic (months to years) and natural exposure of wild Mozambique tilapia to hypersalinity for a period of months to years have not been conducted. It is likely that the higher scores of uninfected fish are in part a physiological response to living in a hypersaline environment for an extended period of time, but longterm studies are necessary to validate this postulate.