MORPHOLOGY AND GROWTH OF LATERAL-LINE ORGANS OF THE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The morphology and growth of selected lateral line organs of the rainbow trout (Oncorhynchus mykiss) are described. Canal neuromasts of the infraorbital and operculo-mandibular canal of three different-sized trout have been examined by light microscopy. The number of neuromasts and pores, as well as their distribution, is constant in all sizes of fish. However, the area and estimated number of hair cells (HC) of the examined neuromasts increase with size and with a correlation coefficient (r2) of 0.90 and 0.87, respectively. It was found that area and estimated hair cell number of neuromasts increase 6-fold in fish from 10 to 30 cm total length (TL). Based on calculation of the hair cell number in small and large fish, a net addition of 1 and 6 HC per day is suggested for IO and OM neuromasts, respectively.