摘要:

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.

ISSN:0706-652X    

DOI:10.1139/f68-001

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Channel catfish (Ictalurus punctatus) were subjected to 5 or 10 min of anoxia (removed from water) to rapidly increase blood lactic acid concentration metabolically. BloodpH decreased as blood lactic acid concentration increased. Respiratory rate increased in fish with lowered bloodpH and with increased blood lactic acid concentration during the 10 min after fish were returned to water after anoxia. Fish not treated had a mean bloodpH of 7.8. BloodpH decreased in catfish subjected to anoxia 5, 10, and 15 min and decreased further when the fish were returned to water. Lowered bloodpH was associated with loss of equilibrium and death in catfish subjected to transportation and handling.

ISSN:0706-652X    

DOI:10.1139/f68-002

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Rainbow trout: (Salmo gairdneri) anesthetized in 100 mg/liter of M.S. 222 at 12 C excreted the drug in free and acetylated forms via the urine during a 24-hr recovery period in freshwater. Of the M.S. 222 excreted, 77–96% was acetylated. Blood levels of free drug in anesthetized trout approximated 75% of the anesthetic concentration, but the amount of acetylated M.S. 222 was relatively insignificant. The blood and urine were cleared of the two fractions of M.S. 222 in 8 and 24 hr respectively. Low levels of aromatic amines of natural origin occurred in blood and urine and were subtracted from measurements of M.S. 222. Intraperitoneal injections of 10–100 mg/kg of M.S. 222 did not induce anesthesia; however, the 24-hr pattern of drug excretion was similar to that observed after anesthesia by immersion. Only 15–21% of the injected dose was found in the urine, suggesting a second route of drug elimination.

ISSN:0706-652X    

DOI:10.1139/f68-003

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Trout were collected and identified from 66 streams or stream systems of different size and gradient. Total dissolved solids (T.D.S.) andpH were determined on most streams. Size and profile of streams to a large degree determined the species of trout present. Large streams, with drainage area over 130 km2, were predominantly occupied by steelhead. Small streams, drainage area under 13 km2, were predominantly occupied by cutthroat. Streams less than 120 km2in drainage area with steep gradients, and emptying directly into the sea, usually supported steelhead, as did large rivers. Those which dropped steeply and then levelled and ran through several miles of sloughs usually supported cutthroat. Where both species occurred, cutthroat were most often predominant in the small tributaries and headwaters, and steelhead in the lower reaches of the main stream. StreampH's were usually lower in winter than in summer, but had no obvious effect on trout distribution. Many cutthroat streams had high T.D.S. readings in the lower reaches in summer and low T.D.S. readings in these areas in winter. Otherwise there were no marked differences between steelhead and cutthroat streams in terms of T.D.S.

ISSN:0706-652X    

DOI:10.1139/f68-004

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The final swimming speed of juvenile largemouth bass,Micropterus salmoides(Lacépède), was reduced markedly at oxygen concentrations below 5 or 6 mg/liter in tests at 25 C in a tubular chamber in which the velocity of water was increased gradually, at 10-min intervals, until the fish were forced by the current permanently against a screen. At levels above 6 mg/liter, the final swimming speed was virtually independent of the oxygen concentration. The performance of bass that had been acclimated overnight to elevated carbon dioxide levels was not materially affected by the highest tested concentrations of free carbon dioxide, averaging 48 mg/liter, at any tested level of dissolved oxygen.For juvenile coho salmon,Oncorhynchus kisutch(Walbaum), at temperatures near 20 C and carbon dioxide concentrations near 2 mg/liter, any considerable reduction of the oxygen concentration from about 9 mg/liter, the air-saturation level, resulted in some reduction of the final swimming speed. The performance of the salmon was impaired much more markedly than was that of the bass by the same reduction of the oxygen concentration. At oxygen concentrations near and above the air-saturation level, high concentrations of free carbon dioxide averaging 18 and 61 mg/liter had a depressing effect on the final swimming speed of coho salmon even after overnight acclimation. However, this effect decreased at reduced oxygen concentrations. No measurable effect of free carbon dioxide concentrations near 61 mg/liter was evident at 2 mg/liter dissolved oxygen, and concentrations near 18 mg/liter had little or no effect even at moderately reduced dissolved oxygen levels after overnight acclimation of the salmon to these carbon dioxide concentrations.

ISSN:0706-652X    

DOI:10.1139/f68-005

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

A method is described for the fluorimetric determination of cortisol in 1-ml aliquots of salmonid plasma. Validation experiments are presented which indicate that the reliability of the method is satisfactory. The method provides the means for the determination of low cortisol concentrations, such as those encountered in hypophysectomized or resting salmonids (0.01–0.05 μg/ml).

ISSN:0706-652X    

DOI:10.1139/f68-006

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The autumnal and over-winter limnological characteristics of two small eutrophic lakes differed considerably from those of a third eutrophic lake; all were close to each other in the southwest interior of British Columbia. Thermal and chemical stratification was well defined in Marquette and Corbett lakes because local topography provided protection from wind action; stratification in the more exposed Courtney Lake was ill defined. Average wind velocities during summer and autumn on Courtney Lake were 4.3 times as great as, and more unidirectional than, those on Corbett Lake and probably Marquette. Complete natural autumnal oxygenation and circulation in Courtney Lake provided comparatively high concentrations of dissolved oxygen which permitted the over-winter survival ofSalmo gairdneriandRichardsonius balteatus. Although Marquette and Corbett lakes were isothermal in late autumn, oxygen concentrations were well below saturation levels and circulation was probably incomplete. Consequently oxygen depletion during winter was severe andS.gairdneriandSalvelinus fontinaliswere subject to over-winter mortality.Experimental circulation of Corbett Lake, just prior to ice cover, confirmed the hypothesis that incomplete autumnal oxygenation is a cause of "winter kill" of fishes. Artificial autumnal circulation of the lake provided an oxygen concentration sufficient to prevent overwinter fish mortality. However, over-winter mortality of the entire fish population did occur in the control lake, Marquette (incompleteautumnal oxygenation) but not in Courtney Lake (completeautumnal oxygenation).

ISSN:0706-652X    

DOI:10.1139/f68-007

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Catostomus commersoniiandC.macrocheilusare sympatric in three major drainages of British Columbia. Morphological analysis employing a character index and discriminant function analysis of allopatric and sympatric populations revealed that hybrids were in 9 of the 11 lakes examined in which both species occurred. Presumed F1hybrids made up an average of 7% of the individuals of the combined populations where hybrids occurred. There was no evidence of backcrossing or swamping.Segregation in spawning time and habitat was not apparent in four confined inlets which have migrations of both species. Some lakes supporting both species were found to have inlets in which only one species spawned. Temporal isolation was absent but habitat isolation was present in some areas of Cluculz River, an outlet with diversified habitat. Where segregation was apparent,C.commersoniispawned in shallow gravelly areas andC.macrocheilusin deep sandy areas. Artificial crosses of the species, two backcrosses involving hybrid females, and microscopic examination of hybrid testes failed to show any effective postmating isolating mechanism. An interaction of temporal, habitat, and postmating isolating mechanisms was not considered sufficient to prevent swamping. Ethological isolation is inferred to be of major importance in reducing initial hybridization. No explanation was found for the apparent failure of hybrids to successfully reproduce.Hybridization could not be attributed to environmental factors commonly associated with this phenomenon. Males of one species entering the spawning act with males and a female of the other species is considered the main cause of hybridization. Mis-mated individuals, however, have much opportunity for conspecific matings at other times. There was no evidence of reinforcement of isolating mechanisms despite the probable occurrence of hybridization in some areas for at least several hundred years. Characters of each species were as distinctive in the areas of sympatry as in the areas of allopatry. Natural selection against individuals producing hybrids is apparently slow.

ISSN:0706-652X    

DOI:10.1139/f68-008

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Coho salmon (Oncorhynchus kisutch) fed a diet deficient in folic acid for 24 weeks developed megaloblastic, normochromic macrocytic anemia. The anemia was further characterized by the presence of poikilocytic erythrocytes which were observed in stained preparations of peripheral blood. These abnormally shaped cells appear to be an important aid in the identification of folic acid deficiency. The anemia disappeared when the deficient fish were fed a recovery diet containing folic acid for 8 weeks.

ISSN:0706-652X    

DOI:10.1139/f68-009

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Studies on the isopodMesidotea entomon(Linnaeus) from 1961 to 1964 in the two Chignik lakes, Alaska, showed that at least part of the population was benthic during daylight and pelagial at night. In Chignik Lake the isopod was most abundant in association with organic and mud bottoms and areas where salmon carcasses accumulate. Abundance decreased from early to late summer, perhaps because of a postreproductive mortality. It is suggested that males grow faster than females, though both sexes mature at age I+ and that growth terminates with maturation. Most reproduction apparently occurs in early summer but some ovigerous females were found as late as September. Length at maturity in both sexes was less than reported by other workers in Arctic marine populations. Mature isopods were smaller in the upper lake (males 40–46 mm,; and females 29–38 mm,) than in the lower lake (males 41–65,; and females 29–47 mm,) of the Chignik River system. Females in the upper lake had a higher average fecundity and a greater increase in fecundity per unit increase of length than those in the lower lake.

ISSN:0706-652X    

DOI:10.1139/f68-010

出版商:NRC Research Press    

年代:1968

数据来源: NRC