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Show 1878.] REV. S. J. WHITMEE ON THE HABITS OF FISHES. 133 When swimming in a placid condition, the anterior portion of the dorsal fin in fishes is seldom elevated; hence the spines which occupy this position are laid back more or less closely, and are often scarcely visible1. The anal fin is also often not fully expanded; but I have not usually seen this so marked as in the dorsal. O n the least fright up goes the dorsal, and the spines are at once elevated. As an example of how slight a cause will suffice to produce this change, I may mention that, before writing the last sentence, I rose from my desk and lightly tapped the front of m y aquarium. The anterior dorsal fins of its inhabitants (previously laid back) were instantly elevated, and all assumed the attitude of attention. Under the influence of great anger or fear, such as would be caused by the presence of a carnivorous fish in the aquarium, the dorsal fin is raised to its extreme height, and the spines, both of the dorsal and anal fins, are very prominent. The scales all over the body are also more or less raised, and with them, of course, any other dermal appendages the particular fish may possess. This causes it to assume larger proportions than under ordinary circumstances. I believe the spines are elevated under the influence of fear as well as by anger. I was once trying to catch a Tetrodon nigropunctatua which was in m y aquarium, when it inflated itself and elevated the fine spines with which its body was covered, and which were previously buried in its loose and flabby skin. This of course was under the influence of fear. And this appears to give a hint as to the purpose for which this fish and those of the genus Diodon inflate themselves. W h e n I have observed fishes chasing each other, apparently in playfulness rather than anger, I have often seen them swim at each other with open mouths as if to bite. But when they have appeared to intend a serious attack they have always turned suddenly round and lashed at one another with the caudal fin. I believe serious fighting is always done with the tail. And from their anatomy one would naturally expect this to be the chief mode of attack in most fishes. I incidentally mentioned this way of fighting by fishes in a paper recently sent to the Society, in which I described an attack made by some small fishes on an Antennarius2. These little things were evidently in great dread of their carnivorous neighbour. But, like small birds in presence of a bird of prey, they could not keep at a distance, but continually tried to torment it. In attacking it they always took care to strike at its posterior part, although this was protected by a block of coral. I said, in the paper referred to, that this mode of attack by the tail ought to be very effective in the case of an Acanthurus, and that it m a y account for the armature of the Acronuridse. In connexion with this subject I will mention a thought which has often occurred to m e as to the chief purpose served by fishes' 1 Drawings of fishes usually represent them with all the fins fully expanded aud the spines prominent; but this is not their ordinary condition. 2 See P. Z. S. 1875, p. 545. |
