Cytological survey of the walleye (Stizostedion vitreum, M.) pituitary gland in relation to annual temperature cycle and its reproductive cycle

Abstract

The value of the walleye (Stizostedion vitreum, Mitchill) as a resource and as a member of the biotic community necessitates an accurate description of its reproductive endocrinology and a means of monitoring its reproductive status. This has been accomplished by a cytological survey of the pituitary of 100 walleyes from navigational pools 6 and 7 of the upper Mississippi River. Gonadal tissue was also removed and analyzed to determine the specific stage of the fish's reproductive cycle. Pituitaries were removed through a dorsal flap in the cranium during 1972 and 1973. The average diameter of gonadotrop cells was 10.59 u during March. This decreased to 8.79 u in July and a gradual increase occurred following the July value. Eta, MSH and thyrotrops followed this trend. In March eta cell diameters were 8.99 u, MSH cells were 8.34 u and, in April thyrotrops measured 8.04 u in diameter. These cell diameters decreased to 6.79 u for eta cells, 7.06 u for MSH cells and 6.7 u for thyrotrops. The gonadal cells increased in size and maturity from 472.8 u in March to 616.8 u in May. The optimum temperatures for spawning of 6.1 degrees C to 17.2 degrees C occurred from the beginning of March until the end of April. This corresponds with time of decreasing cell diameters seen in the pituitary. Presently the appearance of the pituitary cells, expecially gonadotrops, suggests a normal, unaltered condition. Unintentional or accidental disturbance of the habitat, most probably the parameter of temperature, would produce a change in the cycle of gonadotrop size changes.