514 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



tlie pike; A. adunca, in the "May-fish"; A. lahiata, in the eel; and A. 

 constricta, in the sturgeon. 



Biesing mentions a Trichina cyprinorum, but all attempts to develop 

 trichina in fish have so far been unsuccessful. Quite recently I have 

 fiiade experiments with goldfish, feeding them with meat which con- 

 tained trichina, but the trichina passed through the intestinal tube. The 

 " fish trichina '- which are from time to time spoken of in the newspa- 

 pers are, therefore, probably- myths. 



A very dangerous and troublesome parasite is the " fish-leech," which 

 lives on the skiu and the gills of fish, often in such numbers as to tor- 

 ment the ix)or fish. We find the Fisclcola geometra on fish of the genus 

 Cyprinus, the salmonoids and the pike, the F. respirans on the barbel, 

 and the P. fasciata on the ," Wels." The Branchiohdella lives on craw- 

 fish, the Ris^trioMeUa on lobsters, while others live on salt-water fish and 

 mollusks. 



Also among the crustaceans we find a number of parasites which live 

 on the blood of fish, the so-called " fish-louse," remarkable for a pecu- 

 liar regressive metamorphosis during their development. 



The young are very lively and resemble small crustaceans, but when 

 they have reached their permanent place of sojourn, only those organs 

 remain which are necessary for feeding and propagating. 



Of the very large number of these parasites, I only mention the 3r- 

 gasilus Sieholdii on the carp and pike, the Lamprogena pidchella on the 

 " ori^e," the Lernwocera on the carp, the pike, and the codfish, the Ach- 

 theres percarum on the perch, the Tracheliaste^ polycopus on the barbel, 

 and the Argiilus foJiaceus on the carp ; the last mentioned of which I had 

 frequent occasion to observe in my goldfish i^onds. These parasites 

 ■seem not to do special harm ; still I found it advisable to counteract 

 their spreading by draining the ponds from time to time and by remov- 

 ing the parasites. 



I do not believe that more developed crustaceans, which form an ex- 

 cellent food for trout, can hurt the fish-eggs, but there are quite a num- 

 ber, such as the Aiiceus, Cymothoa, &c., which live as parasites on fish. 



Among the insects the water-beetles and their larvse, principally the 

 Bytiscus, AciUus, and Gahjmhetes, are justly considered enemies of fish. 

 I have seen how a Dytiscus marginaUs killed a Mexican salamander six 

 inches in length, for whom it was to serve as food, by biting it in the 

 neck. The larvte of the dragon-fly are also said to hurt the fish. 



In passing to the vertebrates, we find that the fish themselves are dan- 

 gerous enemies of their own kind. Not only will it happen that a male 

 trout with an utter lack of gallantry will eat the eggs instead of impreg- 

 nating them, but many fish, which are considered harmless vegetarians, 

 actually turn cannibals, and, especially at a more advanced age, devour 

 the eggs and young fish. This is the reason why there are so frequently 

 no vouug fish in goldfish-ponds containing strong and healthy male and 

 female fish, whilst those eggs— few in number— which by the water 



