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,
European flounder eyes usually migrate to the right side of the fish and what appears to be its upper surface is in reality its right side. In about thirty percent of individuals, its eyes move to the left and the left side becomes uppermost. The fish has a small mouth at the end of its bluntly pointed snout. The upper surface is fawn, olive green or pale brown with spots and larger patches of darker brown and some irregular reddish spots. The under surface is opaque pearly-white giving the fish its common name of "white fluke". The lateral line is nearly straight