It should also be remembered that fish food (after cooking) must not be given too 

 v/arm, nor should it be deteriorated. Care is also to be taken that neither poisonous 

 substances nor bone splinters ncr indigestible ingredients (over-heaLed proteins) are 

 mixed with the food. 



Rancid fats contain free fat acids and will irritate the intestines of fishes, and 

 decayed food is altogether injurious on account of: 



(1) the large number of living bacteria it contains, and 



(2) through the ptomaines and catabolic products, incidental to the metabolism 

 of said bacteria. 



Very important in regard to fish food — although still little known — is the taste 

 (savour) and general wholesomeness of the food. The best of food, if merely designed 

 from the viewpoint of nourishing qualities will give poor results if the fish is averse 

 to it or cannot tolerate it very well, 



E, Creative Forces and C onditions of Life in the Pond 



1. The Catabolic Cycle of the Pond . 



In contrast to "autotrophic" plants, fish, like all other animals are not constituted 

 to convert inorganic nutriments into body-building, organic matter. Fish requi.re a constant 

 supply of organic substances in order to exist and to grow. They are dependent upon the 

 catabolic cycle of plant life. 



The natural foodstuffs of fish consist of aquatic organisms, called here aquatics, 

 for short. Let us study, therefore, the catabolic cycle of the pond, namely the transfor- 

 mation of inorganic matter into organic substance, that is, into fish sustaining nutriments 

 and their conversion back into original inorganic matter. 



The accompanying sketch attempts to clarify t,he elementary principles of this cycle, 

 but these only, since many details of it are still little known today. Under the influence 

 of sunlight and summer heat, the plant, through its powers of assimilation produces organic 

 substances out of inorganic, nutrient salts (nitrogen, chemical combination of phosphate, 

 potassium, calcium, magnesium, sulphur, iron, sodium, silica, chlorine, water, carbonic 

 acid, and organic substances. The source of energy here is sunlight and heat. 



The plants, in turn, that is, the submerged water flora, such as algae and plankton — 

 algae constitute — in the state of freshness as well as in the form of detritus of dis- 

 integrated organisms — the aliments of aquatics. 



Fig, 5. Schematic view of tlie constructive part of the inaterial cycle in 

 the pond. The destructive activity of bacteria is not illustrated; it can 

 start at every organic link and lead back to the original nutrient substance, 



27 



