ECTOPIC OSSICLES ASSOCIATED WITH METACERCARIAE OF APOPHALLUS-BREVIS (TREMATODA) IN YELLOW PERCH, PERCA-FLAVESCENS (TELEOSTEI) - DEVELOPMENTAND IDENTIFICATION OF BONE AND CHONDROID BONE

This paper describes the development and tissues in mineralized ossicl es in the musculature of Perca flavescens infected with metacercariae of the trematode Apophallus brevis. Analysis involved light microscopy , transmission and scanning electron microscopy, X-ray scanning electr on microprobe analysis, and tetracycline labelling. Two to 14 days pos t-infection, fibroblast-like host cells stream towards the parasite cy st forming a fusiform cellular capsule. By 14 days post-infection the capsule differentiates into an inner hypertrophied layer, an extensive middle layer of fibroblast-like cells, and a thin outer layer of flat tened fibroblast-like cells forming a fibrous sheath at the capsule/mu scle interface. From 21-35 days post-infection, a bony tissue is depos ited periosteally in an equatorial ring around the cyst. With time, ad ditional tissue is secreted over the ring increasing its thickness and advancing the matrix front towards the poles of the ossicle. Plump os teoblast-like cells cover the developing ossicle and may become trappe d within the matrix in lacunae encapsulated by collagen. By 63 days po st-infection, medium-sized ossicles are morphologically similar to lar ge cysts from perch captured in the wild; ovoid with two polarized can als, but lacking acellular or lamellar bone-like tissue. Mineralized o ssicles contain calcium, phosphorus and oxygen. Large ossicles retriev ed from perch given multiple doses of tetracycline revealed discrete f luorescent bands, indicative of incremental growth. Fully developed os sicles are composed of two skeletal tissues, an inner region of chondr oid bone and an outer region of acellular, lamellar bone.