EXPERIMENTAL FISH EMBRYOLOGY 565 



*Sagittarla; species natans, pusilla or mlcrofolia. Excellent both aa decoratlTe and 

 oxygen producing. Strong growing plants. 



Salvlnla; floating plant excellent aa cover for fry. 



Spatterdock; broad light green leaves, q^ulte ornamental, excellent plant. 



Valliaineria; long ribbon-like leaves, plant in back of aquarium. 

 *Utricularia; species vulgaris or minor: good for fry to hide in, highly decorative. 



Water lettuce, floating. 



Water hyacinth, floating. 



THE FEEDING OF FISH : 



"Overfeeding kills fish more frequently than underfeeding." It should be remembered 

 that fish are cold-blooded animals (even the tropicalal) and that moat of them can survive 

 for considerable periods without any food whatsoever. There are several simple rules that 

 should be stated: 



1. See that there is variety in the food. Alternate between living and dry food, or 



between different mixtures of dry food. 



2. The food particles must be small enough for the fish to digest. Uningested food 



simply leads to contamination of the tank, and should be removed daily. 

 5- Feed frequently rather than too much. Tropicals should be fed more often than 



other fish, some fanciers feeding small amounts 3 times each day. 

 h. The amount of food varies with the 



a. Species 



b. Season (temperature and activity). Feed less in winter than in summer.' 



c. Breeding or non-breeding. 



d. Stage of development (fry to adult). 



The oft-stated iniles that you should "feed what they can eat in 5 minutes" or "feed 

 only as much as they can catch before it hits the bottom of thd tank" are too 

 general to be of value. One should study different species, under various condi- 

 tions, and observe the amount Ingested prior to apparent, even though temporary, 

 satisfaction. An adult Oryzias or Platy will do well on two worms (Tubifex or 

 Enchytrea) per day, alternated with a small pinch of dry food. 



There are many specific foods recommended, each fancier devising his own formula. 

 This should indicate the wide latitude of fish tolerance of foods. The most common foods 

 will be listed below. 



Living Foods : 



A. Plant material - fish need their "salads" too. Algae, Duckweed, and Water 



lettuce are occasionally eaten by fish. 



B. Animal material - 



Artemla - the brine shrimp which can be purchased (General Biological Supply 

 House) in large numbers and raised in salt solutions- Day old brine shrimp 

 are excellent food for fish fry. 



Daphnia - and other small Crustacea are very good. Can be sifted out so that 

 smaller specimens are given to fry of 3 weeks or older. Carapace of older 

 specimens may be harmful to young flah. 



Drosophila - the common fruit fly used in Genetics courses, a natural food 

 which can be raised easily in the laboratory. Vestigial mutant is preferred. 



Earthworms - generally too large but may be cut or chopped up. 



Euchytrea - white worms, excellent, even good for fry when finely chopped. 

 These may be cultured in damp humus, in a cool and dark environment by feed- 

 ing them on ml Ik- soaked bread once each week. Cover the humus with a glass 

 plate to reduce evaporation and, if possible, pass cold nmnlng water 

 through glass tubing submerged in the humus, to keep the culture moist and 

 cool. Allow one month for the culture to get started after inoculation. 



Infusoria - (Protozoa) inadequate for adult fish but excellent for carrying 

 fry through critical first 3 weeks after hatching. Eaise on 'hay infusions 

 and add in small amounts to fry tank. 



* The most aatisfactory plants for laboratory aquaria. 



