EXPERIMENTAL FISH EMBRYOLOGY 



573 



Sea water may be obtained by direct shipment from the seashore, or Turks Island Salt 

 may be added to distilled water to simulate sea water. Sand is placed in the bottom of 

 the U to 6 gallon all-glasa aquarium, adequate for one pair of fish. The original salt 

 water line must be Indicated on the aquarium and this line maintained by the semi-weekly 

 addition of distilled water to replace that lost by evaporation. Direct and intense (sun) 

 light should be avoided. 



Sea horses may be fed entirely on small Guppyl, Mosquito Larvae, Enchytrea (white 

 worms) Tublfex (red worms), and brine shrimp. Fresh water food cannot survive for long In 

 a salt water aquarium, hence there must be no overfeeding. Brine shrimp live naturally in 

 the same environment as the sea horses, and are excellent food for the fish. Brine shrimp 

 do better at higher temperatures (up to 100 '-'F. ) and In slightly hypotonic sea water. The 

 occasional addition of some wilted lettuce is advised. The success of a Sea Horse colony 

 depends largely upon the success of a Brine Shrimp culture as food. 



The female sea horse deposits her fertilized eggs in the brood pouch of the male where 

 they are incubated for from 6 to 7 weeks. The breeding period is March through June. The 

 young fry are fed on Protozoon infusions or on the smallest of the brine shrimp. 



Little Is known of the normal development of these eggs and embryos, but since the 

 adults can now be reared In the inland laboratory, it is expected that they will provide 

 new fruitful material for investigation. 



CHARACTERISTICS OF THE ADULT FISH: ORYZIAS LATIPES 



Oryzias latlpes has a wide distribution In China and Japan except in the mountains. 

 It is found in ponds, stagnant pools-, running streams and rice fields. The adults measure 

 from 20 to '"-O mm. in length with an average of about 50 mm. The wild species is blackish- 

 brown while the cultivated species is orange or white, with or without black spots. There 

 are no color changes with breeding activity. The embryos begin to show coloration about 

 one week after hatching. 



The sexes may be distinguished by the following characters: 



MALE 



FEMALE 



Copulatory organ 

 Anal fin 

 Anal fin rays 



Ventral fin 



Dorsal fin 



Anal opening 



Breeding season 

 (April-October) 



Sometimes anal fin 



Parallelogram 



Rarely branching: 17-21 



Barely reaches anterior margin 



Long; reaches base of caudal fin; 



notch at posterior margin. 

 Small and circular 



Body slender; stream- lined 



None 



Triangular 



All bifurcated terminally: 

 19-21. 



Large; reaches past anus 

 to anal fin. 



Short; lobular; rounded at 

 posterior; no notch. 



Large and elliptical; nipple- 

 like U.G. papilla as akin 

 fold posterior to the anus. 



Abdomen swollen with eggs. 



REPRODUCTIVE PHYSIOLOGY 



The ovary of Oryzias is single and enormous, making the female easily distinguishable 

 from the male. In the mature fish it contains hundreds of follicles, each with an egg in 

 some maturation stage. The ovary Itself is saucer-shaped with a membrane across its dor- 

 sal surface, the various sized follicles projecting into the lumen beneath this membreine. 



The mature eggs rupture their follicular walls, without hemorrhage, and emerge into 

 the ovarian lumen. This process requires from 20-6o minutes (see Eoblnaon and Eugh, 19^1) 

 and generally takes place shortly before daylight. There is slight constriction of the 

 egg aa it emergea, with evidence of muscular aid from the follicular wall or the ovarian 

 stroma. 



