yj2 EXPERIMENTAL FISH EMBRYOLOGY 



should be reduced so that the egga will not be covered with algae. (See section on Bepro- 

 ductive Physiology eind Embryology of Oryzias for further details, and see papers by vari- 

 ous authors such as Goodrich, Robinson, Solberg, and Waterman.) 



THE JEWEL FISH, HEMICHROMUS 



These fish are somewhat temperamental and random pairs will not necessarily be con- 

 genial. Combinations must be tested and when a congenial pair has been brought together 

 they should be left together permanently. 



The Jewel Jlsh is rather large and should be provided with a 15 gallon tank for each 

 pair. They are voracious eaters, consuming large numbers of Tublfex and much oatmeal- 

 shrimp mixture. The latter food is made by cooking oatmeal and adding to it dry shrimp 

 commonly used alone as fish food. The tank must be cleaned frequently. 



The female turns a brilliant pink in color when about to breed, which may be as fre- 

 quently as every 7 to 10 days at 80°-8'4-°F. The fish generally attach their eggs to the 

 bottom of the tank, first excavating a clear circular area in the sand or gravel. Taking 

 advantage of this tendency it is well to place, on the bottom of such a tank, broken 

 pieces of a flower pot or crockery, onto which the fish will attach their eggs. These 

 pieces of crockery may then be removed and the early development studied. The fish develop 

 very rapidly (See Noble, Kunpf, and Billings, 1958). 



THE MULTI-COLORED PLATY; PLATYPOECILUS 



These live bearing Poeciliid fish are found in Mexico in the vicinity of the Elo 

 Papoloapan and Elo Panuco where the waters are slightly alkaline (pH tolerance of the fish 

 is 6.U - 8.0) and the temperature variable (temperature tolerance 65°F. to 90°F. with op- 

 timum at 75°F.). Dr. Myron Gordon of the N. Y. Aquarium has collected many specimens on 

 expeditions to Mexico and has distributed them freely for research purposes. 



These fish breed frequently and may drop as many as 80 young at a time. They are less 

 apt to devour their young than are the Gupples, but should be separated from their young 

 shortly after birth. The best aquarium temperature for breeding is 75°F. and the water 

 should be very slightly alkaline. Food is alternated between Tublfex or Enchytrea and 

 mixed dry granular food. The fish may be kept In colonies but gravid females should be 

 Isolated Just before dropping their young. 



The two species, P. maculatus and P. varlatus, are rather common now, the former be- 

 ing so variable in color that there are hardly two fish with similar markings. The major 

 types are (1) Greyish blue with crescent markings; (2) Eedish brown with speckles; (3) 

 Dark fish with black stripes and some black scales. The Gold Platy is a mutation in which 

 the black pigment has been lost and the yellow xanthine base has been exposed. The colors 

 are no bar to crosses, the varieties and species Interbreeding freely. In fact the Platy 

 may be crossed with the Swordtalls. There is now on the market a Platy-Swordtall hybrid 

 known as the Montezuma Swordtail and another, the Black Swordtail, which is a hybrid be- 

 tween the Mexican Swordtail and the Black Platy. Dr. Gordon has worked out the genetic 

 story in considerable detail, linking it with the inheritance of a type of fish (melanotic) 

 cancer. The embryology of these fish has been worked out (See Tavolga & Eugh, 19^+7) • 

 Combined with the known genetic make-up, embryologl cal studies would be highly instruc- 

 tive. (See particularly papers by Gordon.) 



HIPPOCAMPUS HUDSONIUS: THE SEA HORSE* 



Since It Is now known that the brine shrimp, whose eggs can be kept in a dry condi- 

 tion for a long period, can be cultured in salt water and then fed to sea horses, these 

 curious fish can now be maintained in the fresh-water laboratory and the unique method of 

 rearing the young studied. 



* Available through Beldt's Aquarium, 21!+! Crescent. Avenue, St. Louis, Missouri. 



