Benign effect of the fish parasitic isopod Ceratothoa cf. imbricata on Selenotoca multifasciata (Scatophagidae) from Australia

Occurrence of infestation with the isopod, Alitropus typus M. Edwards (Crustacea: Flabellifera: Aegidae) on commercially important freshwater fishes of Kerala, India

Rapidly rising temperatures and increasing organic load in the inland and coastal waters has led to a significant increase in parasite population. The isopod Alitropus typus infestation on fish in these waters have become more frequent, causing mortalities in both wild and cultured fishes. The present study was aimed to investigate the infestation on different fish hosts, mean intensity, prevalence, environmental influences on the parasite abundance and the histopathological changes it causes in the host. A total of 219 isopod specimens were collected from 149 infested fishes in two districts of Kerala, India. Among the different fish hosts, Channa striata was found to be the most susceptible, followed by Catla catla, Cyprinus carpio, and Wallago attu, with 81%, 10%, 7%, and 2% occurrence, respectively. The prevalence and mean intensity of infestation were found to be 69.8%, 44.4%, 68.2%, 62.5% and 1.33, 4.25, 1.26, 1.80 in C. striata, W. attu, C. catla, and C. carpio, respectively. The parasite abundance was directly influenced by temperature. The histopathology of affected gill tissues showed epithelial lifting, rupture of secondary gill filaments, vacuole formation and hemocytic infiltration. The findings indicated that the isopod parasite, A. typus had a negative impact on fish health and appearance, causing economic losses to the small scale farmers/fishermen. This is the first reported record of the infestation of isopod parasite, A. typus on the Indian major carp C. catla and C. carpio from India.

Negative effect of ectoparasite burdens on the condition factor from farmed tilapia Oreochromis niloticus in the Yucatan, Mexico

Nile tilapia (Oreochromis niloticus Linnaeus, 1758) is one of the most important aquaculture species in the world, and, when introduced, the ectoparasites of Nile tilapia have followed. Currently, farmers worldwide consider these ectoparasites harmless, but intensities can reach up to 1000 individuals per fish in tropical regions. In this cross-sectional study, we used the condition factor to estimate the potential effects of low (45 ± 31 ectoparasites per fish) and high (295 ± 191) ectoparasitic burdens across 28 tilapia farms and included the analysis of the effects of 44 management and environmental variable from the farms. A stepwise procedure in a multiple linear regression analysis retained the variables that explained the most variance, which was the ectoparasitic burden (57 %). We found significantly higher values of the condition factor in Nile tilapia with low ectoparasitic burden than in those with high ectoparasitic burden. Additionally, Nile tilapia with a high ectoparasitic burden weighed less than half than those with a low burden (102 ± 105 g versus 230 ± 128 g, respectively). We also found a significant non-linear, negative relationship between the ectoparasitic burden and the relative condition factor values per fish, which was most likely due to an increase in gill mucus caused by the ectoparasitic burden that depleted energy in the Nile tilapia. The economic consequence of the ectoparasitic burden translated roughly into a loss up to 12-15 % in profit margin per ton of fish, based on the price of Nile tilapia in the Mexican market.

Hooked on you: shape of attachment structures in cymothoid isopods reflects parasitic strategy

Background

Parasite attachment structures are critical traits that influence effective host exploitation and survival. Morphology of attachment structures can reinforce host specificity and niche specialisation, or even enable host switching. Therefore, it is important to understand the determinants of variation in attachment structures. Cymothoid isopods are striking ectoparasites of fishes that include the infamous ‘tongue-biters.’ They are known to parasitise hosts in one of four qualitatively distinct anatomical regions. Here, we quantify variation in cymothoid attachment structures — hook-like appendages called dactyli — and test whether differences in dactylus shape are correlated with parasite mode (where they attach), allometry, or both, using multivariate ordinary least squares regression. We also assess the influence of shared ancestry on shape using a molecular phylogeny to weight our models using phylogenetic generalised least squares regression.

Results

We find clear differences in shape between externally-attaching and internally-attaching cymothoids but also between anterior and posterior dactyli across various species with the same attachment mode. Allometric effects are significant for anterior but not posterior dactyli. Mouth-attaching species show greater shape variability than gill- and mouth-attaching species. We find no evidence that there are clade-specific patterns of association between parasite mode and dactylus shape.

Conclusions

Parasite mode appears to be the main driver of attachment morphology. This likely reflects several components of parasite ecology including feeding and functional demands of attachment in different microhabitats. Geometric morphometric approaches to the quantification of shape variation of simple structures is an effective tool that provides new insights into the evolvability of parasite attachment.

Understanding growth relationships of African cymothoid fish parasitic isopods using specimens from museum and field collections

Cymothoid isopods are a diverse group of ectoparasites of fish species, and are particularly conspicuous as they are large and attach to the body surface, mouth, and gill chamber of fish hosts. These parasites transition from juvenile to male to female, and how their size changes with ontogeny and correlates with host size is not well understood. To better understand these relationships, data from field and museum collected samples of South Africa were combined to test for the associations between host and parasite length for three mouth and one gill chamber-infesting genera (Ceratothoa, Cinusa, Cymothoa, and Mothocya respectively). Generally, the number of parasites collected from 90 h of museum surveying was similar to that of seven, one-week long field collections. For two of the three mouth-infesting parasites, parasite and host size were significantly and positively correlated for males and females, but not juveniles. For gill chamber-infesting parasites, female and male parasite sizes were weakly and not significantly correlated with host size. These results provide the first morphometric data and growth relationship data for African cymothoid species and their fish hosts, and demonstrate the value and efficiency of using museum collections in ecological research.

Spatial variation in the parasitic isopod load of the Japanese halfbeak in western Japan

Cymothoid isopods (family Cymothoidae) are commonly found parasitizing diverse fishes, including commercial species. However, the effects of these parasites on host body condition are still poorly known. Here we investigated the spatial variation of the effects of parasite infection on host body condition, using the parasitic load of the cymothoid Mothocya parvostis on the Japanese halfbeak Hyporhamphus sajori at 4 sampling sites in western Japan. M. parvostis prevalence at each site (41.6-74.4%) was higher than that known for other fish host-cymothoid systems (usually less than 30%). The number of isopods in infected hosts, the reproductive status of female isopods (i.e. ovigerous/non-ovigerous), and the body size of female and male isopods relative to the size of their hosts were not significantly different among sites. However, at the site where human activity was most intense, M. parvostis infection had a significantly negative effect on host body condition. These results suggest that the effect of cymothoid infection on host body condition might be benign under natural conditions but becomes detrimental in habitats that are unsuitable for the host, such as highly human-impacted areas.