Competition 121 



body weight per day and held at water temperatures warm enough for 

 growth. Water was changed in all aquaria at two-day intervals through- 

 out experiments extending from 43 to 80 days. Controls received no other 

 treatments, but experimental a(|uaria received varying amounts of meta- 

 bolic water obtained by stocking a small container with a large number of 

 fish for 30 to 40 minutes or until thev had difficultv in breathinij^. Fish in 



J ^ CD 



aquaria receiving metabolic water gained slightly or lost weight wliile 

 control fish gained 150 to 275 per cent of original weight. 



As yet, there is no exact agreement among investigators as to the 

 causative agent responsible for tliis inhibition of growth and reproduction. 

 One believes it is a hormone-like substance, another a substance that 

 created a vitamin deficiency. When fish-conditioned water was given to 

 rats for drinking they lost weight and died after 45 to 50 days.^- These rats 

 displayed characteristic symptoms of Vitamin Bi deficiency. 



In the Far East where fish are grown in boxes in streams there is no 

 growth inhibition, although the density of fish in the boxes amounts to 

 as much as 50 per cubic meter. Here the metabolic waste is carried away 

 by the current. Yashouv ^- thinks that this action of metabolic waste may 

 represent a defense mechanism (for slowing population growth) of the 

 existing population. 



Mraz and Cooper ^^ found little relationship between population 

 density of adult carp (within the range of 75 and 450 pounds per acre) 

 and the weight of young carp present with them at the end of the first 

 summer (3 months), Figure 5.1. Adult carp were stocked in May just 

 prior to the spawning season, and the ponds were drained in August or 

 early September. These adult fish always produced a spawn; when less 

 than 100 pounds of adult carp per acre were stocked, the fish usually 

 gained in weight; a loss in weight followed, when adults were stocked, 

 at rates of 150 to 450 pounds per acre. Average size of these young carp 

 ranged from 2.7 to 5.0 inches after 3 months, and the weight per acre 

 of young carp ranged from 98.4 to 308.7 pounds. As the carp were stocked 

 just prior to the spawning season, there was no inhibition in spawning, but 

 growth of adults and young may have been affected later. 



Among game and pan fishes in hatchery ponds no clear effect of 

 crowding upon growth (where adequate food was available) and repro- 

 duction has been demonstrated, although one may assume that accumula- 

 tion of waste may function as a growth inhibitor. 



Larimore ^- demonstrated a very significant difference in the numbers 

 of ova carried by female warmouth living under different conditions. For 

 example, a female warmouth of 5.3 inches from Venard Lake (Ilfinois) 

 contained 40,400 ova in various stages of development, while a female 

 of the same length from Park Pond contained only 12,500 ova. Venard 



