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,
Dagetichthys lusitanica Dagetichthys lusitanica Dagetichthys lusitanica, commonly known as the Portuguese sole, is a species of flatfish native to the eastern Atlantic Ocean. Little is known of the abundance or behaviour of this fish, and the International Union for Conservation of Nature has rated its conservation status as being "data deficient". The Portuguese sole grows to a standard length of about . The general shape is oval, tapering somewhat towards the tail. Like other flatfish, the body is flattened laterally and the fish lies on its side, with both eyes on the right side; the upper eye is slightly in front of