When hatchery-reared and wild landlocked Atlantic salmon (Salmo salar) parr of the same age and size were permitted to compete for social dominance and for food in aquaria, twice as many hatchery salmon attained dominance as wild salmon. Dominant hatchery salmon also showed a higher intensity of aggressiveness than dominant wild salmon, displaying a higher and more variable mean nipping rate. Socially dominant salmon ate more food per fish than subordinates, but there were no statistically significant differences in feeding rate between dominant hatchery and dominant wild salmon, or between subordinate hatchery and subordinate wild salmon.Hatchery salmon displayed lower feeding rates than wild salmon when they were held in separate compartments of an aquarium and compared at three temperatures. This difference in feeding rate probably was not a reflection of differences in adaptation to temperature or food preference, but, rather, was the result of interference with feeding caused by the more intense social interaction among hatchery fish.It is suggested that high levels of aggressiveness may contribute to mortalities of hatchery-reared salmon planted in streams because of loss of feeding time, excessive use of energy, and increased exposure to predators.

Toxic effects of aqueous aluminum complexes in neutral and basic media to rainbow trout fingerlings were investigated under constantly flowing, controlled conditions of concentration, pH, and temperature. Toxicities of various concentrations were highly pH dependent. Dissolved concentrations over 1.5 ppm aluminum caused drastic physiological and behavioral aberrations as well as acute mortality. Toxic effects of suspended aluminum, while they are more noticeable at lower concentrations, are not as concentration dependent as those of dissolved forms. The safe concentration of either dissolved or suspended aluminum is well below 0.5 ppm. Mortalities among test animals ceased almost immediately after aluminum exposures were concluded. Recovery times for fish exposed to the various tests were proportional to the severity of the test conditions and to the length of exposure. Normal growth resumed almost immediately in fish from the less severe tests, and after a period of a few weeks in fish from the more severe tests. After up to four months recovery the average weight of fish surviving both chronically and acutely toxic aluminum concentrations is markedly below the control average.

A quick and reliable method of measurement is necessary to set standard limits on the amount of suspended sediment to be tolerated in streams near land‐use operations. Turbidity measurements may be useful if a major portion of the total turbidity is contributed by settleable solids, if a relationship exists between turbidity readings and weight per unit of volume of suspended sediment, and if a reliable meter is available. Water with turbidity readings greater than one JTU (Jackson Turbidity Unit) is generally composed mostly of settleable solids unless distorted by color. Non‐filterable and total dissolved solids contribute variable amounts of light penetration reduction. Percentage contribution to turbidity of settleable solids is highly variable from sample to sample and from station to station. A high correlation exists between turbidity readings and weight for individual sediment types of suspension, but a poor relationship exists when sediment type is varied. Experiments conducted on the Hach model 2100, the Hellige, and the Jackson Candle turbidimeters resulted in a highly significant difference (α = 0.01) between readings on the same sample of suspended sediment. Turbidity is a questionable measure of suspended solids in water. A more accurate index would be suspended solids measured gravimetrically.

the eels and others have become flattened from side to side as the basses and are known as compressed. Fishes of Maine are either rounded or compressed in body form. Covering the fish externally is a layer of mucus secreted by the glands of the skin. This mucus protects fish from external infection. Fishermen have long been cautioned to wet their hands before handling fish which they intend to return to the water. Handling with dry hands would remove a large amount of this protective covering and leave the fish exposed to fungus and bacterial invasions. Immediately under the mucus lies the epidermis and under the epidermis are embedded the scales. The scales are laid down shortly after the fish is hatched and reflect changes which may occur in the life history of the fish. Age of fish can be determined from the number of year marks, and periods of good growth and poor growth can be detected from the spacing of the growth rings on the scale. Ages of fishes in this book refer to the number of completed year marks on the scale and conform to the manner in which we ordinarily report the age of a human. Among fishes of Maine the lamprey eel, hornpout, and freshwater sculpin are without scales. Scales of Maine fishes may be divided into the cycloid type and the ctenoid type. Cycloid scales are usually small, and embedded deeply in the skin. Trout and salmon are examples of fish with cycloid scales. Ctenoid scales have several rows of spines along their posterior or exposed edge. These spines, or ctenii, give the fish a rough or spiny feeling. Bass and white perch are examples of fish having ctenoid scales. Fins of fishes are thin folds of skin supported by rays, spines, or both. Fish are frequently classified either as "soft-rayed" fish such as trout, or as "spiny-rayed" fish such as bass. Rays are finely segmented and often branched while spines are unsegmented, unbranched, and usually hard. Counts of rays and spines, since their number is reasonably constant, are frequently of value in identification of closely allied forms. Paired fins include the pectorals located behind the gill openings and the ventral or pelvic fins located on the lower side of the body. Fish are frequently classified as to whether the fins are positioned posteriorly or anteriorly on the ventral side or belly of the fish. Most "advanced" fishes have the ventral fins placed under, or nearly under, the pectoral fins when the location is described as thoracic. If the ventral fins are in front of the pectoral fins then the location of the ventral fins is described as jugular. When the ventral fins are posterior their position is considered abdominal. Unpaired fins include the dorsal, adipose, caudal or tail fin, and the anal fin. Although a fish swims primarily by muscular movements of its body it depends on the caudal fin lending power to the movements, on the dorsal and anal fins for stabilizing the movement, and on the pectoral and ventral fins for steering and maneuvering. Fish obtain their oxygen from water passing over the gills. Closing the g...

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