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,
Demersal fish benthic fish are denser, with negative buoyancy so they can lie on the bottom without any effort. Most demersal fish are benthopelagic. As with other bottom feeders, a mechanism to deal with substrate is often necessary. With demersal fish the sand is usually pumped out of the mouth through the gill slit. Most demersal fish exhibit a flat ventral region so as to more easily rest their body on the substrate. The exception may be the flatfish, which are laterally depressed but lie on their sides. Also, many exhibit what is termed an "inferior" mouth, which means that the mouth