Salmon Essays (1909 words) - Salmon, Oncorhynchus, Thamnophis

Salmon What species would travel over 2000 miles just to have young and then die? It has been said that anyone who has not seen a wild salmon has not seen what a fish should be. Salmon was the common name applied to fish characterized by an elongated body covered with small, rounded scales and a fleshy fin between the dorsal fin and tail. In this paper I will be discussing history of studying salmon, the life cycle, spawning and mating behaviors; which has much to do with the total reproduction of salmon. Salmon were studied earlier than some may think. Experiments were done by men that date back to the mid-1600s. These experiments involved catching salmon in fresh water, tagging them, and then catching them again when they return to the same place, around six months later. These experiments were doubtful and it was not until the beginning of the 1900's that proof was available that the salmon returned home. (Shearer) Although usually drab in color before the breeding season, which varies with the species, members of the salmon family develop bright hues at spawning time. The male, during this mating season, usually develops a hooked snout and a humped back. In many diverse taxa, males of the same species often exhibit multiple mating strategies. One well-documented alternative male reproductive pattern is 'female mimicry,' whereby males assume a female-like morphology or mimic female behavior patterns. In some species males mimic both female morphology and behavior. We report here female mimicry in a reptile, the red-sided garter snake (Thamnophis sirtalis parietalis). This form of mimicry is unique in that it is expressed as a physiological feminization. Courting male red-sided garter snakes detect a female-specific pheromone and normally avoid courting other males. However, a small proportion of males release a pheromone that attracts other males, as though they were females. In the field, mati ng aggregations of 5-17 males were observed formed around these individual attractive males, which we have termed 'she-males.' In competitive mating trials, she-males mated with females significantly more often than did normal males, demonstrating not only reproductive competence but also a possible selective advantage to males with this female-like pheromone. In the competitive mating trials, the she-males were successful in 29 out of 42 trials. The normal males won out in only 13! The authors ask the question: Why aren't all males she-males given such an advantage? (Mason, Robert T., and Crews, David; Female Mimicry in Garter Snakes, Nature, 316:59, 1985.) Comment. Among the fishes, bluegills and salmon (and probably many others) have female-appearing males competing with normal males. Abstract: The influence of sperm competition and individual mating behaviour in an externally fertilizing species of fish, the Atlantic salmon (Salmo salar), is estimated from video observations of multiple-male spawnings and subsequent paternity analyses. One male dominated the paternity during polygamous spawnings, fathering more than 80% of the progeny in a single nest. Behavioural analyses of the spawnings showed that the first-mating male had sperm precedence in 6 out of 10 cases. In three of the other spawnings, sperm limitation likely influenced individual success, as the first-mating male had participated in a large number of spawnings. In the final, nearly simultaneous spawning, male size was more important than the 0.6-s difference in spawning times. Thus, male fertilization success can be influenced by a variety of factors, including sperm precedence, male size, and spawning history. Back to Table of Contents Before mating, one parent excavates a nest for the eggs; after the eggs are deposited and fertilized, the female stirs up the stream bottom so that earth and stones cover the eggs and protect them. The eggs hatch in two weeks to six months, depending on the species and the water temperature. During the migrations and nest-building activity that precede mating, neither the females nor the males consume food. In the life cycle of the pacific salmon, nature recycles the parents to feed the babies. Mature salmon leave the Pacific Ocean as saltwater fish, never again to eat as they battle their way up the Columbia River to spawn in the home stream where they were born. Those born in the upper reaches of the Columbia River's tributary stream, the Snake River, travel more than