Clinostomum is a genus of parasitic trematodes found worldwide, infecting a wide range of hosts, including freshwater fishes, snails, birds and occasionally humans. In this study, clinostomid metacercariae were collected from Nile tilapia raised in fish farms in the Upper Tana River region, Kenya. The prevalence of infection was 17.2%, with metacercariae infecting the skin, gills and buccal cavity of the fish. Using light microscopy, scanning electron microscopy (SEM) and molecular methods targeting both nuclear ribosomal (ITS1, 5.8S, ITS2) and mitochondrial (COI) regions, the metacercariae were identified as C. cutaneum, C. phalacrocoracis, C. tilapiae and Euclinostomum heterostomum. The three species of Clinostomum have previously been reported to infect fish or piscivorous birds in Kenya, while this is the first report of E. heterostomum in this country. SEM analysis revealed new ultrastructural features of C. cutaneum, including an excretory pore surrounded by minute spiny papillae, an everted cirrus and dome-shaped papillae on the tegumental area around the genital pore. The cirrus lacked basal papillae, showing morphological variation between the adult and metacercarial stages. Our study, therefore, provides new insights into the phenotypic identification of flukes that may be pathogenic to fishes and humans and, therefore, of scientific and practical importance.
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RBINS Staff Publications 2025
Otoliths, or ear-stones, are calcareous components in the static-acoustic organs of teleost fishes with a characteristic morphology. As such, they are widely used in fisheries because of the information stored in them concerning, for example, environment, age, and so forth. Otoliths of three lethrinid species Lethrinus borbonicus (Valenciennes, 1830), L. lentjan (Lacepède, 1802), and L. mahsena (Forsskål, 1775) were collected from fish caught along the Red Sea coast of Yemen. Images taken with a scanning electron microscope were used to determine their characteristics. Twenty-two characters were defined to describe the shapes of the otoliths. Eleven measurements of distance between selected features were used for a linear regression and multivariate analysis to characterize the species by their otoliths. The results illustrate ontogenetic changes for different age groups based on the recorded shapes. All three species show a linear relationship between the total length and the morphometric measurements. A linear discriminant analysis shows marked differences between the otoliths of the three species and emphasizes the importance of the measured variables. Otoliths of L. lentjan and L. borbinicus are more similar to each other and differ from those of L. mahsena. A comparison with previously published otoliths of the species studied from other areas confirms an intraspecific uniformity across larger geographic distances, making the characters useful for diagnostic purposes.
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RBINS Staff Publications 2022
