Abstract
This study involved 334 specimens of mullet, Mugil platanus, captured monthly in the estuarine region of Cananéia, São Paulo State, Brazil, from July 1988 to June 1989, and examined for the presence of gill parasites. Parasitological inspections revealed the occurrence of the following groups: Trichodina sp., Monogenoidea, Copepoda, and Hirudinea. Only four mullets were not parasitized. Total weight and total length of all 334 mullet specimens examined were used for adjusting the weight-length relationship curve and calculating the relative condition factor (Kn). The 118 specimens infested with monogenoideans on average had lower weights than expected (Kn < 1.0), and the 81 fish co-infested with Copepoda, Monogenoidea, and Trichodina sp. showed a Kn < 1.0. The other infested and non-infested mullets had a Kn > 1.0. It was possible to infer that gill infestation with monogenoideans alters mullet weight, especially in the presence of co-infestation with Trichodina sp. and copepods.
Highlights
Specimens of mullet, Mugil platanus, from Cananéia, São Paulo State, Brazil, have been previously studied by Ranzani-Paiva & Ishikawa (1996) and Ranzani-Paiva et al (1997)
Examination of the mullets with gills infested by different parasite groups showed that the 81 fish co-infested with copepods, monogenoideans, and Trichodina sp. had a Kn < 1.0 (Table 2)
The relative condition factor (Kn) has been used by Silva-Souza (1998) to show that ocular parasitism by Diplostomum (Austrodiplostomum) compactum metacercariae impairs the health of Plagioscion squamosissimus specimens from the Tibagi River
Summary
Mugil platanus, from Cananéia, São Paulo State, Brazil, have been previously studied by Ranzani-Paiva & Ishikawa (1996) and Ranzani-Paiva et al (1997). The relative condition factor (Kn), first defined by Le Cren (1951) and used initially by Eckmann (1984) to select females of Brycon cf erythropterus induced to spawn by hypophysation, corresponds to the ratio between observed and theoretically expected weight for a given length. It allows statistical comparison between the estimated value of Kn and the central value Kn = 1.0 (Anderson & Gutreuter, 1983; Verani et al, 1997; Andrade-Talmelli et al, 2001; Romagosa et al, 2001)
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