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,
Hypselodoris kanga white. The inner edge of each gill is reddish orange in the upper quarter, deep blue in the mid region and white in the basal quarter. The smooth outer side of each gill is orange-red in the upper quarter and the rest has a background colour of light blue with a row of large yellow spots. The two outer corners of each gill are bordered with red at the tip becoming dark blue at the base. This species can reach a total length of at least 70 mm and has been observed feeding on yellow sponges from the genus "Dysidea".