Kokanee salmon lake acidity. As a result, the kokanee was believed to have gone extinct in the 1940s. In 2011 a few fish were found in an isolated lake on Mount Fuji. The Japanese kokanee varies from its sea-going sockeye relative in a few ways. The black kokanee breeds in March at a depth of 30–40 feet, while sockeye salmon breed in the fall and have a different number of gill rakers than the kokanee. In addition, the black kokanee is much darker in color than the sockeye or any other kokanee population. The fish has been introduced to different lakes around
Pain in fish that the absence of C-type fibres in cartilagenous sharks and rays indicates that signalling leading to pain perception is likely to be impossible, and the low numbers for bony fish (e.g. 5% for carp and trout) indicate this is also highly unlikely for these fish. Rose concludes there is little evidence that sharks and rays possess the nociceptors required to initiate pain detection in the brain, and that, while bony fish are able to unconsciously learn to avoid injurious stimuli, they are little more likely to experience conscious pain than sharks. A-delta-type fibres, believed to trigger avoidance reactions, are common