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Whether fish are nourished by water.
One inquires further about the nourishment of things that swim and, first, whether fish are nourished by water.
1. It seems so. For that which enters into fish and nourishes them is their nourishment. But they are nourished by the entry of water, as is said in the text, and therefore, etc.
2. Moreover, "we are nourished by the same things from which we take our existence." But fish take their existence from water in terms of their domain. Therefore, they are nourished by water.
3. Moreover, they cannot live without water. This would not be the case if they were not nourished by water. Therefore, etc.
To the contrary. According to Aristotle in the second book of On Generation, a simple element does not nourish. Therefore, fish are not nourished by water, since it is a simple element.
One must respond to this that things that swim are not nourished by water alone either as food or as an object. But some of them are nourished by the slimy matter [ muscillago] that is in the water, others are nourished by the dust of the earth, still others are nourished by plants, and others by flesh, and this occurs according to the diversity of their complexions. Thus those in whom the heat becomes more intense live on flesh; those in whom it becomes less intense, live on slimy matter, and those that approach more to an elemental nature live on the dust of the earth. Nevertheless, although they are not nourished by water as if by an object, water still contributes to them in two ways. The first has to do with the distribution of the nutriment, because they take in their nutriment with water mediating it. Moreover, they use water to temper the natural heat, just as breathers do with air.
But one must understand that although fish take in seawater, they still do not draw in that which is earthy in the water but only that which is sweet. For the sweet can be separated from that which is earthy, as is evident in a wax-like instrument that is very concave and almost completely closed. If this is left in the sea for a day and a night, it will be filled with fresh water, and the salty and earthy parts will cling to the outside, as we showed in the book On Meteorology. And this is why the meat of marine fish is not salty but sweet, although they live in salt water.
1. On to the arguments. To the first, one must reply that water does not enter into fish in the same way as nutriment, but rather for the distribution of the nutriment.
2. To the second argument one must reply that "we are nourished on the same things from which we take our existence" applies to principles near to us but not to those that are remote from us. Now let us grant that animals arise from the elements as if from remote principles, but from compounds like the humors as if from proximate principles. Therefore, they are not nourished by the elements but rather from the humoral moistures which are their proximate principles. Or one can say that just as they exist on water from their domain, so those compounded are nourished by other [humoral moistures] from their domain.
Whether fish eat their young.
One inquires further as to the nutriment of fish. And first one asks whether fish eat their young.
1. And it seems not. Because every animal has a natural love for its offspring [fetus]. But eating the offspring does not stem from love, and therefore, etc.
2. Moreover, other animals do not eat their offspring; therefore, for the same reason, neither do fish.
The Philosopher says the opposite.
One must reply that of all the animals fish do eat their young rather a lot. The reason for this is that fish are very gluttonous and have impaired senses. Gluttony arises from the cold of the stomach, for a hot stomach is good for digestion, but bad for the appetite, according to Galen. But a cold stomach is bad for digestion but sharpens the appetite. But fish have a cold stomach, and this is why they are so gluttonous.
Moreover, they have impaired senses, and this is why, when fish see their young, they are not able to discern whether they are their own or belong to another. And they are especially gluttonous. And this is why they eat their own young as well as those of another without distinction.
1. On to the arguments. To the first, one must reply that an animal's love for its own offspring is natural, nevertheless in an accidental way an animal can be blinded to or impeded in this in some measure, namely, owing to an inability to distinguish them because it does not recognize them. This even occurs in perfect animals like the human, who sometimes kills his brother thinking that he is someone else.
2. To the second argument one must reply that although this occurs in fish in particular, nevertheless it can also occur in others. For, if a wolf is wounded, it is said that all the others surround and devour it. Thus, since a wolf is a very gluttonous animal, when it perceives its prey and sees that another wolf is incapable of seizing it, it does not spare it more than it does any other animal. And the same holds true for the rapacious animals with hooked talons. And, moreover, some pigs have been seen in Cologne to eat their young, and this was owing to their gluttony and to the absence of nourishment, etc.
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