Salmon Essay Example For Students

Salmon Essay What species would travel over 2000 miles just to have young and then die? Ithas been said that anyone who has not seen a wild salmon has not seen what afish should be. Salmon was the common name applied to fish characterized by anelongated body covered with small, rounded scales and a fleshy fin between thedorsal fin and tail. In this paper I will be discussing history of studyingsalmon, the life cycle, spawning and mating behaviors; which has much to do withthe total reproduction of salmon. Salmon were studied earlier than some maythink. Experiments were done by men that date back to the mid-1600s. Theseexperiments involved catching salmon in fresh water, tagging them, and thencatching 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 the1900s that proof was available that the salmon returned home. (Shearer)Although usually drab in color before the breeding season, which varies with thespecies, members of the salmon family develop bright hues at spawning time. Themale, during this mating season, usually develops a hooked snout and a humpedback. In many diverse taxa, males of the same species often exhibitmultiple mating strategies. One well-documented alternative male reproductivepattern is female mimicry, whereby males assume a female-like morphology ormimic female behavior patterns. In some species males mimic both femalemorphology and behavior. We report here female mimicry in a reptile, thered-sided garter snake (Thamnophis sirtalis parietalis). This form of mimicry isunique in that it is expressed as a physiological feminization. Courting malered-sided garter snakes detect a female-specific pheromone and normally avoidcourting other males. However, a small proportion of males release a pheromonethat attracts other males, as though they were females. In the field, matingaggregations of 5-17 males were observed formed around these individualattractive males, which we have termed she-males. In competitive matingtrials, she-males mated with females significantly more often than did normalmales, demonstrating not only reproductive competence but also a possibleselective advantage to males with this female-like pheromone. In thecompetitive 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 arentall 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) havefemale-appearing males competing with normal males. Abstract: The influence ofsperm competition and individual mating behaviour in an externally fertilizingspecies of fish, the Atlantic salmon (Salmo salar), is estimated from videoobservations of multiple-male spawnings and subsequent paternity analyses. Onemale dominated the paternity during polygamous spawnings, fathering more than80% of the progeny in a single nest. Behavioural analyses of the spawningsshowed that the first-mating male had sperm precedence in 6 out of 10 cases. Inthree of the other spawnings, sperm limitation likely influenced individualsuccess, as the first-mating male had participated in a large number ofspawnings. In the fina l, nearly simultaneous spawning, male size was moreimportant than the 0.6-s difference in spawning times. Thus, male fertilizationsuccess can be influenced by a variety of factors, including sperm precedence,male size, and spawning history. Back to Table of Contents Before mating, oneparent excavates a nest for the eggs; after the eggs are deposited andfertilized, the female stirs up the stream bottom so that earth and stones coverthe eggs and protect them. The eggs hatch in two weeks to six months, dependingon the species and the water temperature. During the migrations andnest-building activity that precede mating, neither the females nor the malesconsume food. In the life cycle of the pacific salmon, nature recycles theparents to feed the babies. Mature salmon leave the Pacific Ocean as saltwaterfish, never again to eat as they battle their way up the Columbia River to spawnin the home stream where they were born. Those born in the upper reaches of theColumbia Rivers tributary st ream, the Snake River, travel more than 1,000 milesinland to lay their eggs and fertilize them, roughly one fourth of the distanceacross the United States. Without enough reserves in their bodies to get back tothe Pacific, the adult salmon spawn and die. To spawn, a female salmon scoops anest in stream-bottom gravel by waving her tail and deposits her eggs in thehole. The male releases milt (sperm) into the water that covers the eggs andfertilizes them. Then the female brushes gravel over the eggs, and both parentslie exhausted in the stream until they die. Micro-organisms in the waterdecompose their bodies during the winter, and this process increases thepopulation of micro-organisms in the stream. Come spring, the salmon eggs hatchinto the tiny fish called fry. The first food is the microorganismsin the stream. The Pacific salmon never see their parents, but are actuallynourished by their decomposed bodies. The next step in growth isfingerlings, then young salmon make the dangerou s trip downstream,past dams and waterfalls to the ocean. There they grow into adults, averagingsix pounds in weight. In its life cycle, the pacific salmon takes five forms andsizes: a pea-sized egg, one-half-inch embryo, one- to three-inch fry, four- tofive-inch fingerling, and fully grown, six-pound adult one to two feet long. Women Rights | | EssayBibliography1. Mills, Derek. (1989). Ecology and Management of Atlantic Salmon. NewEngland, New York: Chapman and Hall. 2. Shearer. (1978). The Atlantic Salmon. New York: Halsted Press form 3. Cone, J., ; Ridlington, S. (Eds.). (1996)The Northwest Salmon Crisis: A documentary History. Corvallis, Oregon: OregonState University Press.