BIOLOGY OF SPERM AND ARTIFICIAL REPRODUCTION IN CARP

Although the common carp, Cyprinus carpio, has been cultivated for sev eral thousand years and is produced in large quantities, research on r eproduction has been very limited. Traditionally, spawning occurred na turally in situ in rearing ponds, In slightly improved methods large b reeding ponds stocked with brood fish were devoted to reproduction wit h fry collection in autumn, or in small spawning ponds with collection of larvae a few days after hatching, Controlled reproduction in hatch eries started only in the 1950s. This paper reviews some of the basic work on carp sperm and describes the technologies of artificial reprod uction. The sperm is of a primitive type with uncondensed chromatin an d a small midpiece, As in most teleost fish, the sperm is immotile in the male genital tract and in the semen and is activated after release into fresh water. The initiation of motility is due to the decrease i n osmotic pressure. The structure of the flagellum is rapidly disorgan ized in fresh water and sperm stop moving after 30 a. When dilution oc curs in a 50 mM NaCl solution, the osmotic change is sufficient to ini tiate motility, but the flagellum is not disorganized and swimming las ts a few minutes. Motility depends mainly on endogenous ATP stores, ab out 12 nmol/10(8) spermatozoa, and stops when 50-80% of the ATP is exh austed by hydrolysis. The procedure of artificial insemination include s collection of gametes (from ''hypophysised'' males and females), mix ing in an extender (45 mM NaCl, 5 mM KCI, Tris 2.5 mM, glycine 19 mM, pH 8) in a ratio 1 litre of eggs to 1 litre of diluent and 1 mi of sem en, Sperm motility can be triggered during collection by contamination of the semen with urine; this could interfere with fertilization and, if present, urine should be discarded by pouring out the top part of the tube, The sticky layer of the egg is removed by adding a ''dissolv ing solution'' (20 g urea/1 + 4 g NaCl/1 of water) or milk (diluted 1/ 5 in water) to the fertilized egg and stirring. One hour later the swo llen eggs are transferred to incubators (usually Zug bottles, sometime s 200 litre circular jars).