Observations on the Spawning of the Sculpin, Cottus semiscaber

Abstract

W 7HILE collecting fish from spring creeks near Jackson, Wyoming, on February 20, 1940, our attention was drawn to egg clusters of the sculpin, Cottus semiscaber (Cope). Again the following year, on March 2, numerous egg masses were seen on the under-surface of rocks in the springs where sculpin were collected. Beginning February 15, 1942, the springs were visited numerous times for the purpose of establishing more exactly the time and extent of the spawning season, and for gathering other pertinent data. Two springs were visited regularly: Tanner Spring, with a temperature of 48?'F., and the Government Ranch Spring, with temperatures of 45? to 48?. Both springs are tributary to Flat Creek, Teton County. In the headwaters of both, where the sculpin spawn, the bottom is composed of coarse gravel, interspersed with large irregularly shaped rocks. Tanner Spring contains an abundance of water cress. At lower levels of both creeks the bottoms are excessively muddy. Sculpin do not spawn in the muddy areas. The velocity of the water seemed to make no difference in the choice of a nest rock. Egg clusters were found where the current was rapid and also where it was almost non-existent. During the 1942 season, egg clusters were first seen on March 6 at Tanner Spring. Some had reached the eye spot stage on this date; others were newly laid. Eggs collected then hatched within five days in an aquarium. On March 20, March 25 and April 5, at the same spring, both eyed and uneyed eggs were located. No eggs could be found on the last visit to the spring on April 16. At the Government Ranch Spring the first cluster of eggs (uneyed) was found March 25 (water temperature 45? F.). On April 16, April 28 and May 10, gravid females were located, as well as egg clusters (water temperature 48?). The last eggs, which were eyed, were found May 26. This sculpin's eggs are usually salmon colored; occasionally a light yellow mass of them is seen. They are strongly adhesive and are laid in clusters on the under-surface of rocks (Plate I), rarely on vegetation or on the stream bottom if rocks are available. Shallow, scooped-out depressions or nests, usually occupied by the sculpin, were found under some rocks. Eggs may be removed easily from the rocks without separating from each other. The clusters average in size about 24 x 40 mm., and are usually about the depth of seven eggs. Although no compound clusters were found, occasional egg clusters of slightly different color and in different stages of development were observed close together on the same rock, possibly the product of different females. The individual eggs averaged 2.47 mm. in diameter; those from the ovaries of females ready to spawn measured 2.2 mm. There was an average of 354 eggs per cluster in those collected from rocks, and an average of 629 eggs in the ovaries of females nearly ready to spawn. Measurements and counts were made from six egg clusters.