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I contacted Richard Pillans, the primary author of the article linked to in the question. He told me that he did not know whether the rectal gland was reduced. Researchers are hesitant to capture and dissect the freshwater sharks because of their endangered status.   He did tell me that they have gathered much more data on the movement of the sharks since ...


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I've thought about this many times but enjoyed theorizing on possibilities vs researching evolutionary theory. I like these thoughts above- def agree to certain extent- but it seems to me that: If almost all "fishes" utilize side to side motion/morphology, it seems that this is certainly more efficient, and would be adopted, over many millions of ...


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Yes, at least some fishes have intrinsic lifespans and deaths that are related to their own life-history and not to external forces such as predation or disease. Fishes show three types of senescence. Lampreys, eels and pacific salmon exhibit rapid senescence and sudden death at first spawning. The guppy, red panchax, medaka, platyfish, Indian murrel ...


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Fish do not die from old age, nor do any other animals. Rather, the older the animal gets the weaker it becomes which means that it is an easier target for predators or can easily succumb to disease.



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