Larvae of non-biting midges in the family Chironomidae can be found in association with several species of fish in the family Loricariidae. In this study, we describe the first record of phoretic interaction between larvae of Ichthyocladius sp. and the fish Hisonotus chromodontus in streams in the Amazon basin. Between July 2010 and March 2019, fish were collected from three streams of the Teles Pires River basin in the state of Mato Grosso, Brazil. We investigated the attachment site of chironomid larvae on the body of fish and the frequency of attachment. A total of 1.241 specimens of H. chromodontus were collected, among which nine hosts were found carrying in the ventral region a single Ichthyocladius sp. specimen. All Ichthyocladius sp. were attached to a spicule of fish between the pectoral and pelvic fins, in which they were observed at the fourth developmental stage at the beginning of the cocoon construction (1.50 mm). In addition, a pre-pupa larva (2.60 mm) and an empty cocoon (2.50 mm) were reported. The Loanda stream had the highest occurrence of this type of association (of 12 fish examined, three had larvae). The other two streams reported a lower occurrence: the Baixada Morena stream had three fish associated with larvae amongst 1105 fish examined, whereas the Selma stream had three out of 124 fish infested by larvae. The occurrence of only one larva per host can be related to the small body area of the host fish (average standard length = 26.60 mm and average weight = 0.31 g). We observed that the larvae prefer fixation sites in the vicinity of the pectoral and pelvic fin of the fish, which is presumably associated with the fact that chironomids feed on algae and debris suspended by the movement of loricariids. These streams differ with respect to the presence of riparian forests, which may affect resource availability and thereby influence ecological interactions between the species.
Cymothoids belong to the order Isopoda and are ectoparasites of fishes, and their main parasitism strategies are by penetrating, burrowing, and lodging in the abdominal cavity of the hosts. Due to this complex parasitism strategy, they are considered highly host-specific parasites. We investigated the effects of parasitism of the burrowing cymothoid Artystone sp. on the loricarids Hisonotus chromodontus and Curculionichthys luteofrenatus in the Selma stream, a tributary of the Teles Pires river, Southern Amazon. The hypothesis under study is that parasitism causes negative effects on the feeding, reproduction, and length-weight relationship of the hosts. The presence of alternative hosts was also investigated. The parasitic interaction of Artystone sp. with Curculionichthys luteofrenatus and Hisonotus chromodontus was monitored for one year with standardized monthly collections, and was found to be highly specific when there were no other parasitized fish species. Parasitic castration caused by Artystone sp. occurred in Curculionichthys luteofrenatus and Hisonotus chromodontus hosts, and there was a higher prevalence of infestation in females. The weight-length relationship was lower in parasitized Hisonotus chromodontus hosts, indicating a negative effect on somatic increment, although all hosts had fully replete stomachs and gastrointestinal tracts. The greatest standard-length values for both species were observed in the parasitized hosts. The presence of parasitized young specimens with undifferentiated sex and immature males and females suggests that the parasitic interaction in both species starts at a young age.
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