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 the1900’s 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 aren’tall 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 final, 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 River’s tributary stream, 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 is”fingerlings,” then young salmon make the dangerous 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.
Nature fully recycles pacific salmon. (Atlantic Salmon, in contrast, travel uprivers only 150 to 250 miles long and can return to the sea after spawning. ) Themales of many fish fight for the possession of the females. When a fish isconquered, his colors fade away and he hides his disgrace among his peaceablecompanions, but is for some time the constant object of his conqueror’spersecution. Mr.
Shaw saw a violeny contest between two male salmon that lastedfor a days. The males are constantly teare “In many diverse taxa, males ofthe same species often exhibit multiple mating strategies. One well-documentedalternative male reproductive pattern is ‘female mimicry,’ whereby males assumea female-like morphology or mimic female behavior patterns. In some speciesmales mimic both female morphology and behavior.
We report here female mimicryin a reptile, the red-sided garter snake (Thamnophis sirtalis parietalis). Thisform of mimicry is unique in that it is expressed as a physiologicalfeminization. Courting male red-sided garter snakes detect a female-specificpheromone and normally avoid courting other males. However, a small proportionof males release a pheromone that attracts other males, as though they werefemales.
In the field, mating aggregations of 5-17 males were observed formedaround these individual attractive males, which we have termed ‘she-males. ‘ Incompetitive mating trials, she-males mated with females significantly more oftenthan did normal males, demonstrating not only reproductive competence but also apossible selective advantage to males with this female-like pheromone. ” Inthe competitive mating trials, the she-males were successful in 29 out of 42trials. The normal males won out in only 13! The authors ask the question: Whyaren’t all males she-males given such an advantage? (Mason, Robert T. , andCrews, David; “Female Mimicry in Garter Snakes,” Nature, 316:59,1985. ) Comment.
Among the fishes, bluegills and salmon (and probably manyothers) have female-appearing males competing with normal males. Abstract: Theinfluence of sperm competition and individual mating behaviour in an externallyfertilizing species of fish, the Atlantic salmon (Salmo salar), is estimatedfrom video observations of multiple-male spawnings and subsequent paternityanalyses. One male dominated the paternity during polygamous spawnings,fathering more than 80% of the progeny in a single nest. Behavioural analyses ofthe spawnings showed that the first-mating male had sperm precedence in 6 out of10 cases. In three of the other spawnings, sperm limitation likely influencedindividual success, as the first-mating male had participated in a large numberof spawnings.
In the final, 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 An adult femalesalmon can lay upto 15,000 eggs, depending upon her size. The female fish (hen)creates a depression in the gravel bed of the river by an energetic flapping ofher large tail.
The male (cock) fish swims up beside her and begins to quiver,stimulating the female to release her eggs, at the same time the male releaseshis milt which fertilises the eggs. Once the mating has been completed thefemale again starts to beat the river bed with her tail, this time just abovethe site where she laid her eggs, this causes gravel to wash downstream with thecurrent and cover the eggs. This covering of gravel offers the eggs protectionfrom predators such as eels, ducks and other fish. After spawning, the malefish, now called a kelt, rapidly loses the hooked jaw and bright colourationthat it had developed just prior to the mating season. The male may remain atthe breeding site for days or weeks, guarding the newly-layed eggs. Salmon eggsdeposited in the autumn hatch the following spring The Atlantic and Pacificsalmon demonstrate distinctly different reproductive strategies.
The Atlanticsalmon may return to fresh water to spawn several times while the Pacific salmonconcentrates its reproductive efforts into one large spawning event and thendies (Ward, 1939). The reproductive cells of the Pacific salmon all maturesimultaneously and as a result, these fish have only one chance to breed. Withthe completion of spawning, their lives soon come to an end. Although theAtlantic salmon has the physiological potential to reproduce numerous times, thelong journey to the spawning grounds, as well as the stress of the reproductiveact itself takes its toll. Typically, fewer than 10 per cent of spawningAtlantic salmon return to the ocean, with most of these being females.
Thesefish belong to the salmon family. Most members of this family are valuable foodand a source of excellent game. They are found in both fresh and salt water inthe colder regions of the Northern Hemisphere. Many return from salt water tofreshwater to breed, and the young migrate to salt water from freshwater afterthey reach maturity. The migratory instinct of members of the salmon family isremarkably specific, each generation returning to spawn in exactly the samebreeding places as the generation before it. Even those species that do notmigrate from freshwater to salt water spawn in the same freshwater streams, asdid their ancestors.
The spawning ground of these fish is usually a rapidlyflowing, clear stream with gravel and rocks on the bottom. Bibliography1. 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.
