574 EEPOET OF THE COMMISSIONER OF FISHERIES. 



very large, and the reproductive capacitv of a carp increases great!}'' 

 for the next year or two after it begins to spawn. According to 

 Hessel (1881, p. 871) a female weighing 4 to 5 pounds will contain on 

 an average 400,000 to 500,000 ova. Bay (1880-1S84, p. 161) quotes 

 other estimates, thus: A female of 9 pounds had 600,000 eggs (Bloch); 

 one of 161 pounds had 101,200, one of 25i pounds 203,109 (Harmer); 

 one of 21i pounds had 1,310,750, and one of 16i pounds had 2,059,750 

 (Buckland). 



In the case of a female mirror carp from Sandusky Bay, which I 

 weighed at Port Clinton June 22, 1903, I found that the ova com- 

 prised more than a fourth of the total weight of the fish. The fish 

 before being opened weighed 17 pounds; after the removal of the ova 

 with a,s little loss of blood as possible, the weight was 12 pounds 6 

 ounces, leaving 4 pounds 10 ounces as the weight of the ova. This is 

 27 per cent of the entire weight of the fish and 37 per cent (over a 

 third) of the weight of the remainder of the fish after the ova had 

 been removed.'^ 



This enormous fecundity is undoubtedly an adaptation to compen- 

 sate for the dangers of the exposed condition in which the eggs are 

 left after being laid, since ihej are merelj" scattered about on the 

 vegetation in shallow water and are given no further care or attention 

 by cither of the parent fish. It may also help to explain the remark- 

 able increase in numbers of the carp in our waters in a very short 

 time, for if we suppose that the ordinar}^ enemies of the eggs were not 

 in the habit of searching for food in the kind of locality utilized by 

 the carp for spawning, or at least were not present in large numbers, it 

 is easy to see what an advantage this would give the carp, especially 

 if the conditions were favorable to its growth in other respects. 

 Furthermore, it would not be at all surprising if, as has been known 

 to have happened in other cases, the increase in the quantity of food 

 furnished by the abundant supply of carp eggs would favor the cor- 

 responding increase of some other fish or other animal which finds the 

 eggs good eating. Or possibh^, even, some form which has previously 

 lived on other food may adjust its habits to the new conditions, and 

 come to prey large!}" upon the spawn of the carp. It will rather be 

 surprising if something of the kind does not happen, for in their 

 struggle for sustenance nature's creatures are no respecters of person 

 nor property, and it w^ould be an unusual thing for a rich supply of 

 food to be lying around long without some of them appropriating 

 it. When this does occur, the phenomenal increase of the carp will 

 undoubtedly be checked and the natural balance will again be approxi- 

 mated. One thing that militates against this in the case of the 



"Day (1880-1884, p. 161) says that continued cold weather may prevent carp from spawning, so 

 that the process may last over several weeks or months, while some fish may retain the ova, thus 

 occasioning disease. Bean (1903, p. 169) mentions that confinement of gravid females in a small 

 tank may also cause them to retain the eggs, and he speaks of two fish that died from this cause. 



