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BULI^TIN OF THE BUREAU OF FISHERIES. 



The writer (Wilson, 1923) has recorded the killing of a young buffalofish in 

 an aquarium at Fairport, Iowa, by a female Hydrous triangularis just after she had 

 completed spinning an egg case. 



None of these accounts are very convincing. If the neighbor mentioned by 

 EUes had actually seen a beetle killing his goldfish fry, there was no need of further 

 proof. If he had not, the placing of the two together in a basin of water with the 

 resultant death of the fish certainly did not furnish such proof. There are large 

 water bugs belonging to the family Belostomidse which are just as likely to kill 

 young carp as are the two beetle genera mentioned by Riley. Garman's state- 

 ment is a general one without the citation of anything to prove its validity. The 

 writer, in his record above cited, called attention to the fact that the con- 

 ditions under which the kiUing of the buffalofish occurred were artificial and 

 abnormal. Consequently, while it is highly probable that these large beetles do 

 sometimes kill small fish, we have to admit in all fairness that their guilt has not 

 yet been legally established. It is also worthy of record that while Cybister and 

 Dytiscus and Hydrous are common in nearly all the fishponds at Fairport, no one 

 has ever seen an adult beetle attacking one of the fish fry. 



FISH AS BEETLE EATERS. 



Having ascertained how many and what species of beetle larvae and adults 

 prey upon fish fry, we may turn about and inquire what kinds of fish ordinarily eat 

 beetle food. Our inquiry now is much more easily answered, since it does not 

 involve any watching of the fish. We have simply to examine the contents of the 

 fish's digestive canal to obtain exact information both as to the quality and the 

 quantity of food consumed. Moreover, the beetles eaten are more readily recog- 

 nized than almost any other kind of food. The hard chitin covering of the head of 

 the beetle larva, together with the antennae and mouth parts, remain sufiiciently 

 intact to be readily recognized. For the adults the entire beetle is sometimes practi- 

 cally uninjured and may even make a respectable specimen after a temporary 

 sojourn inside a fish's stomach. In case it is mutilated, there is always enough of 

 the hard chitin parts to render identification easy and certain. 



EVIDENCE FROM FISH BAIT. 



So far as known neither the beetle larvae nor the adults are used anywhere in 

 the United States as fish bait, but there is apparently no reason why they would 

 not make excellent bait. The larva of the horned Corydahs or dobsonfly {Corydalis 

 cornuta) is known to fishermen everywhere as the dobson, crawler, and a variety 

 of other names and is much prized as fish bait, especially for black bass. 



The larva of Hydrous triangularis closely resembles the dobson in size and general 

 appearance, and it is greedily eaten by bass whenever offered to them. Large- 

 mouthed black bass are used in many of the experiments at Fairport, and there are 

 some of them in the tanks most of the time. Hydrous larvae of aU sizes up to full 

 development have been fed to these fish during the summer. They have always 

 eaten the larvae with great avidity, and if they were hungry it sometimes seemed 

 as if the larva did not fairly strike the surface of the water before it was snapped 



