THE PHYSIOLOGY OF THE SPAWNING MIGRATION

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Abstract
Knowledge of the wide range of spawning migrations of fish is summarized by examples of 3 classes[long dash]the codfish and grunnipn for those that live and spawn in the sea, the common eel for those that spawn in the sea but develop to maturity in fresh water rivers, and salmon for those that spawn in fresh water but feed and develop in the sea. Eels spawn east of the Bermudas. During a larval stage of 3 years, the European form travels over 3,000 miles to rivers of northern Europe. Adults leave the rivers and apparently die after spawning in mid-ocean. The American species also spawn in mid-Atlantic but spend only 1 year as larvae. Adult salmon returning from the sea enter their parent streams to spawn and spend 3-7 years in the sea. It is not known how the fish identify their respective rivers of origin. Salmon make the return spawning journey without feeding and die after spawning. Extensive data of changes in chemical composition of salmon muscle during migration and fast, also of the ovaries, which are rapidly developing at this time, are quoted. The tissues store great quantities of fat and protein, which are used to supply energy and growth materials for the gonads during the prolonged fast. A reserve of 6% of the wet weight of muscle is protein, above the 14% of protein in fasting muscle. No carbohydrate is present in muscle but ovarian tissue contains .09%. Measurements of blood pressure averaged 75 mm. Hg in the ventral, and 53 mm. in the dorsal aorta. Why salmon arrive on the river spawning beds in good physiological state but die soon after spawning, no adequate explanation has yet been offered. A bibliography of 110 titles is given.

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