Age determination in fish fish. Johannes Reibisch, working for the Commission of Scientific Investigation of German Seas at Kiel, attempted to use Hoffbauer’s techniques to age plaice ("Plueronectes platessa") but found it difficult to accurately discern annuli. He decided to study a different structure and in 1899 he published the first procedures using otoliths as an aging structure. A fellow scientist also with the German Commission at Kiel, Friedriche Heincke, also frustrated with difficult scale annuli, further studied other structures to age fish. He discovered annuli in the vertebrae, opercula, and pectoral girdle and published his findings in Heicke 1905. The works of Hoffbauer,
Platy (fish) they are olive in color with black marbling or spots on the side of the caudal peduncle. Large males show blackish blotches on the dorsal fin. Unlike some other members of the genus, "X. variatus" has no claw at the tip ]] ray. The fourth pectoral ray shows well-developed serrae (i.e. saw-like notches). They typically have 20 to 24 lateral scales, 10 to 12 dorsal rays and two rows of jaw teeth. Platy is widely used in tropical aquariums. Several different color variations have been developed, such as red, yellow, orange, blue, rainbow (combination of colors) and white. Platy (fish)