Condition factor of Astyanax intermedius Eigenmann, 1908 (OSTEICHTHYES, CHARACIDAE) parasitised by Paracymothoa astyanaxi Lemos de Castro, 1955 (CRUSTACEA, CYMOTHOIDAE) in the Grande River, Serra do Mar State Park - Santa Virgínia Unit, São Paulo, Brazil

Isopods Cymothoidae ectoparasites of fish from the Amazon

Most freshwater species of Cymothoidae are distributed in South America. They have mainly been recorded in the eastern and western regions of the Amazon River basin. However, in this ecosystem, the biodiversity of this group may be greater if the entire Amazon basin is considered. In this regard, the aim of the present study was to provide an updated list of isopod species of the family Cymothoidae that are found in fish in the Brazilian Amazon region and to report on new fish host occurrences and expanded geographical distributions for cymothoid isopods that parasitize fish in the southwestern Brazilian Amazon region. The parasites found in fish specimens were collected, fixed and identified later. We found eight species of Cymothoidae parasitizing different host fish species in the southwestern Amazon region. However, we found 14 species of Cymothoidae throughout the Brazilian Amazon region. Three additional species are thus reported here, which increases the number of species of Cymothoidae in this region to 17. These additional species are also new records for Brazil. Therefore, this study has contribute to expand the knowledge about the distribution and diversity of Cymothoidae in the Amazon basin.

Crustacean parasites of Leporinus affinis, an Anostomidae fish from the Brazilian Amazon

This study investigated the fauna of ectoparasitic crustaceans in Leporinus affinis from Reservoir Coaracy Nunes, in eastern Amazon (Brazil), as well as the parasite-host interactions. The mouth, gills and tegument of 50.9% of the fish examined were parasitized by Argulus chicomendesi, Ergasilus turucuyus and Excorallana berbicensis, and a total of 118 parasites were collected. The dominance was found for E. berbicensis and the higher infestation levels were caused by E. berbicensis on the body surface of the hosts, but E. turucuyus had the highest prevalence on the gills of this host. The cluster analysis revealed higher similarity in the infestations by E. berbicensis and A. chicomendesi in relation to infestation site in hosts. Host sex and relative condition factor (Kn) were not influenced by moderate parasitism, but the abundance of parasites presented negative correlation with weight and Kn of the fish. This is the first study on the parasites of L. affinis showing low species diversity, with moderate prevalence and low parasite abundance.

The parasitic isopod Mothocya nana drives dietary shifts and poorer condition of Brazilian silversides Atherinella brasiliensis

Cymothoids are ectoparasites that may attach to various parts of the fish for molting and reproductive purposes, thus increasing the energetic costs of the host. This study investigated the influence of the parasitic isopod Mothocya nana on the physiological condition and diet of adult Brazilian silversides Atherinella brasiliensis at a sandy beach in southeastern Brazil. We collected 268 A. brasiliensis individuals, of which 230 fish were non-parasitized (mean ± SE total weight [TW] = 16.92 ± 0.38 g; total length [TL] = 127 ± 0.88 mm) and 38 were parasitized by up to 2 isopods (TW = 15.89 ± 0.79 g; TL = 126 ± 1.96 mm). Parasitic prevalence (P) and intensity (I) reached highest values in June 2015 (P = 20.88%; I = 1.31) and were slightly higher on males (P = 17.39%; I = 1.33) than on females (P = 13.07%; I = 1.27). Parasitized fish revealed poorer condition than non-parasitized ones, among which male hosts were especially burdened by M. nana's attachment. The condition factor, the eviscerated condition factor and the fullness index each showed a decreasing trend according to the parasite's development and offspring weight (i.e. increase in egg and larval weight). Parasitized and non-parasitized Brazilian silversides fed mainly on microcrustaceans, but the first group showed reduced phytoplankton intake and was associated with fewer trophic categories in comparison to non-parasitized fish. These dietary shifts revealed correlation with the poorer physiological condition reported for infected A. brasiliensis, whose decreased feeding efficiency is likely related to potential impairment of the filter-feeding mechanism and/or altered behaviour due to pressure atrophy and the increased energetic costs imposed by M. nana's development.

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.

Feeding and reproductive patterns of Astyanax intermedius in a headwater stream of Atlantic Rainforest

ABSTRACT In this paper, we determined diet composition, reproductive periodicity and fecundity of Astyanax intermedius in a headwater stream of a State Park of an Atlantic rainforest. We also evaluated the influence of rainfall, water temperature and fish size on niche width and niche overlap. Sampling was conducted monthly throughout one year in the Ribeirão Grande stream, southeastern Brazil. Diet consisted of 31 food items with equal contribution of allochthonous and autochthonous items. Females were larger than males, and the mean sizes at first maturation were 4.44 cm and 3.92 cm, respectively. Based on 212 pairs of mature ovaries, the number of oocytes per female ranged from 538 to 6,727 (mean = 2,688.7). Niche width and niche overlap were not related to rainfall nor water temperature and only niche width increased with fish size, suggesting that as fish grow, more items are included in diet. Our results suggested that A. intermedius fit as a typical opportunistic strategist which may explain the prevalence of this species in several isolated headwater basins of vegetated Atlantic forested streams where food resources are abundant and distributed throughout the year.

Influence of the flood pulse on the reproduction of Tocantinsia piresi (Miranda Ribeiro) and Auchenipterus nuchalis (Spix & Agassiz) (Auchenipteridae) of the middle Xingu River, Brazil

Abstract This study investigates the influence of the flood pulse on the reproductive biology of the auchenipterids Tocantisia piresi (Miranda Ribeiro, 1920) and Auchenipterus nuchalis (Spix & Agassiz, 1829) from the middle Xingu River in the Brazilian state of Pará. The specimens were collected every three months between April, 2012, and January, 2014, covering four distinct periods (flood, ebb, dry, and filling). The sex ratio, size at first maturity, gonadosomatic index, and condition factor were analysed in the two species, and evaluated in the context of the different hydrological periods. A total of 897 specimens of T. piresi were collected, of which 467 were female, and 430 males, and 383 A. nuchalis (286 females and 97 males). In T. piresi, the sex ratio was biased only in the filling and ebb periods, whereas in A. nuchalis, it departed significantly from the expected ratio of 1:1 in all periods, with a predominance of females. The female T. piresi mature at a smaller size than the males, with the opposite of the pattern being recorded in A. nuchalis. In T. piresi, the breeding peak was observed during the low water periods, whereas in A. nuchalis, the peak was recorded in the flood periods. Male and female T. piresi presented similar positively allometric growth rates, whereas in A. nuchalis, growth was negatively allometric, but rates were different between genders. A higher condition factor was recorded in the females of both species during the ebb period. Overall, the results of this study reveals distinct flood pulse effects on the reproductive parameters of the two auchenipterid species studied; for A. nuchalis the spawning seems to happen at the flood period and for T. piresi at the dry season of the middle Xingu River.