The Breeding Behavior of the Common Shiner, Notropis Cornutus (Mitchill)

Résumé du livre

1. In May an inshore migration in lakes and, in some cases at least, an upstream movement is made by Notropis cornutus. 2. Sexual dimorphism is pronounced. Breeding males have well developed pearl organs or breeding tubercles, are highly colored and reach a larger size than breeding females. The breeding tubercles on the various parts of the body are of value in the fighting which occurs among the males, in driving away predators and in the breeding act. 3. Spawning occurs from May 1 through the middle of July in the northeastern states, beginning usually when the water has reached a temperature of 60° to 65° F. At any one locality spawning lasts about ten days and is limited to the daylight hours. 4. The common shiner may (1) spawn over gravel beds in running water, (2) excavate small depressions in gravel or sand in running water or, (3) utilize the nests built by other species such as Nocomis micropogon, Nocomis biguttatus, Leucosomus corporalis, Semotilus atromaculatus atromaculatus, Exoglossum maxillingua and Campostoma anomalum whether these are built in running or the still waters of shallow pools. They prefer to spawn over the nests of other species when these are available. 5. Hybridization often occurs with Notropis cornutus as one parent largely as a result of their spawning over the nests of other fishes. 6. The number of males that will spawn over one nest varies considerably, there being from one hundred or more over a gravel bed to as few as one male over a small depression. More females are present at the nests than males. 7. Males fight continually for the leading position, the position furthest upstream in the nest. 8. A male shiner recognizes a female and takes a semi-recumbent position alternately from one side to the other when the female approaches from the downstream side of the nest and comes to a position above and slightly downstream from the male. 9. The female reacts to a fish whether it be a male common shiner or another species providing he has taken a position over a nest, head facing upstream and moving slightly from side to side. 10. The female takes the initiative in the breeding act by dipping downward, to lie beside the male. The male throws his caudal peduncle over that of the female, curves his body by bringing his head and tail in close proximity with his pectoral fin underneath the head of the female. The eggs are forced from the female at this moment while she lies, usually on her side, her ventral surface facing upstream and her head pointing toward shore. The entire breeding act is over in a fraction of a second and the details cannot be clearly seen with the unaided eye. 11. Probably fewer than fifty eggs are laid at once. The demersal eggs become adhesive after water-hardening in about two minutes after being laid and drop between the pebbles on the bottom of the nest to which they adhere. When first laid they are orange and average 1.5 mm. in diameter.