1 1 50 FISH CULTURE 



was cut up into small pieces. Two hours afterwards the fish showed a well 

 filled stomach, but no signs of digestion as yet : 4 hours afterwards, signs of 

 digestion were evident ; 5 hours afterwards the contents of the stomach were 

 less in quantitj- ; 6 hours afterwards 2 fish had their stomachs empty, and 7 

 hours afterwards digestion was completed in all the fish. The conclusion 

 drawn is that the spleen is digested 6 to 7 hours after feeding. 



2) Liver : Same preparation as for the spleen. Its digestibility is 

 very different. Some fish were found with their stomachs empty as little 

 as 6 hours afterwards, while in others digestion was only completed 8 hours 

 afterwards. Generally it may be said that digestion is terminated within 

 7 to 8 hours. 



3) Fish lesh : The flesh of freshwater fish was given either separately 

 or together with spleen, liver and shrimps to older fry. The fish used 

 f(;r preparing the food were put into hot water and left there from i to 5 

 minutes according to size ; thej^ were then pressed in moulds after removing 

 the .skin and bone from the biggest. 



Three hours after the meal, the stomach of the fr}- was still quite full ; 



4 hours afterwards digestion was begun, and 6 hours afterwards all the fish 

 had their stomachs empty. The conclusion drawn is that the flesh of fish 

 is complete^ digested 5 to 6 hours after the meal. 



4) Shrimps : Shrimps also were only given during the period previous 

 to the stocking of the pond with fry. The shrimps were first left in boiling 

 water for half to. three quarters of an hour, then pressed in moulds. Only 

 fry which have reached a certain age readily eat shrimps alone ; for younger 

 fry they must be mixed with soft substances such as liver, spleen etc. At 

 first 50 % of shrimps are mixed with 50 % of liver, etc. Then in proportion 

 as the age of the fry increases the proportion of shrimps is increased, until 

 finally shrimps alone are fed to them. 



In the case of the fish receiving shrimps alone digestion was completed 



5 to 6 hours after the meal. 



(5) Larvae of Culex pipiens : These were eaten by the fr\- within a 

 few minutes : i ^/g to 2 ^j^ hours after the meal digestion was begun. The 

 writer counted a maximum of 18 larvae in the stomach of one fish. Diges- 

 tion was terminated 4 to 5 hours after the meal. An interesting fact 

 is that the chitinous parts of the larvae remain in the stomach of the fish for 

 a very long time, probably owing to derangements impeding the peristal- 

 tic movement of the .stomach. The same fact is observed when Daphnidae 

 are given. 



(6) Daphnidae : The larvae of Daphnia magna and Daphnia pulex 

 were given. They were immediate!}" devoured by the fish, which ate about 

 20 per head per meal. The first signs of digestion were observed 2 ^/g hours 

 after the meal, and digestion was completed 3 ^/2 to 4 ^/g hours after the 

 meal. 



Conclusions. — Liver requires twice as long as shrimp for digestion, 

 lyiver and spleen require most time, the natural food (Culex, etc.) requires 

 the least time. Fish-flesh and shrimps are intermediate between these 

 two groups with regard to the period of digestion. The causes of the easy 



