How to obtain it. 101 



likely again to be eradicated. Some kinds do much better than 

 others, and among these perhaps one of the best is the Limnea 

 peregra. 



Crustaceans in the shape of fresh water shrimps (Gammarus 

 pulex] are also very easily introduced, and should be put into the 

 stream flowing into the pond, where they will at first be more at 

 home, and they or their progeny will soon drop down into the 

 pond and stock it. The fact must not be overlooked that some 

 crustaceans are parasitic on fish. Some knowledge is therefore 

 requisite, before introducing living creatures into a trout pond, or 

 a serious mistake may possibly be made. I once had a 

 consignment of fish from abroad, and on arrival they were closely 

 examined before being turned out, and were found to be infested 

 bv a leech. These creatures caused the fish much annoyance, if 

 they were not otherwise hurtful. Each fish was carefully 

 examined and the pests removed, and after being passed twice 

 through salt baths, and performing quarantine, they were found to 

 be quite clean, and were then turned out. Seven of these leeches 

 were put into a glass jar for further examination, and a couple of 

 sticklebacks were introduced. A leech immediately stuck to one 

 of them, having hold of the jar at the same time, and in spite of 

 the utmost endeavours of the fish, the leech held it for fifteen 

 seconds or more, and then relinquished its hold of the glass and 

 stuck to the fish with both extremities, to its evident great 

 annoyance. The others soon followed suit and took hold also. 

 Next day, however, the tables were turned, four of them having 

 taken inside berths. The remaining three still adhered firmly to 

 one fish. These leeches, when examined under the microscope, 

 were found to be infested by scores of smaller parasites. 



1 ' Great fleas have little fleas 



To live upon and bite 'em ; 

 Little fleas have lesser fleas, 

 And so ad infinitum." 



This occurrence suggests the exercise of great care in 

 importing foreign fish lest we import foreign parasites and plagues, le 

 as so frequently in the past. All imported fish should be 

 carefully examined, dipped, and quarantined, before being passed 

 into British waters. 



