摘要:

Size-selective mortality decreases or increases the actual and back-calculated lengths of an age-group, while at the same time altering the shape and variance of its length frequency distribution only slightly or not at all. An index of intensity of selection (r) can be calculated from the difference in computed length (d) between the penultimate annulus at agenand the terminal annulus at agen−1, together with the standard deviation in length (s); it isr = 1.349d/s, and represents the difference in mean instantaneous mortality rate between the two halves of the frequency distribution. Instantaneous rates of increase in weight can be computed from length data by multiplying the difference between the natural logarithms of length 1 year apart by the exponent in the weight–length relationship. When there is size-selective mortality, the difference between the rate (GX) based on observed weights in successive years differs from the true rate (G) based on the terminal length differences computed from scales. Similarly the instantaneous rate of decrease in numbers (Z) differs from the rate of loss of weight or ponderal mortality rate (ZW). It is found that G−GX= ZW−Z. "Lee's phenomenon" may be caused by selective mortality or by biassed sampling. Unlike selective mortality, biassed sampling produces onlypositiveLee's phenomenon (back-calculated lengths from older fishlessthan those calculated from younger fish), regardless of whether it is the smaller or the larger fish that are favoured by the sampling gear. The use of incorrect growth rates can lead to rather large errors in estimates of production of a stock. Errors in computation of yield, due to using numerical instead of ponderal mortality rates, tend to be much smaller.

ISSN:0706-652X    

DOI:10.1139/f69-051

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Two forms of the copepodPseudocalanus, which differ only in size, coexist in two semi-landlocked fiords on Baffin Island. The large form possesses the same number of chromosomes as the small but its chromosomes are conspicuously larger and contain about seven times as much DNA. Due to polyteny, the large form has a greater cell size and a slower development rate than the small form. The large form, having an essentially annual life cycle, matures later than the small form. Two generations of the small form may be produced in a summer with only the first reaching maturity. As the fiord waters are warmer, the small form is smaller and develops faster than its counterpart in nearby seas. The large form may represent an evolutionary attempt to restore normal arctic size and development rate in the fiords. In the cold waters of the sea, the slow development rate of the large form might lead to an excessively long life cycle, perhaps biennial. This may explain the apparent absence of the large form outside the two fiords. The polytene form may be a new species but, as the taxonomy of the genus is indefinite, a new name is deferred.

ISSN:0706-652X    

DOI:10.1139/f69-052

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Observations of feeding behavior demonstrated thatEngraulis mordaxcaptures food by two distinctly different kinds of attack—biting and filtering.Artemiaadults in high concentration evoke a biting attack andArtemianauplii in high concentration evoke a filtering attack.Feeding trials withArtemiaadults produced the equationw = 18.1 T0.359W1.138, wherewis weight of food consumed in milligrams, T is time in minutes, and W is fish weight in grams. Density had no effect over the range of 1–25 organisms per liter. Trials with adultArtemiaalso indicated that the maximum capacity of the digestive tract in milligrams is 93.3 W + 53.1.Feeding trials withArtemianauplii produced the equationn = 6.31 T0.970W0.520D0.594, wherenequals the number of nauplii consumed. Density (D) had a noticeable effect over the range 292–1120 organisms per liter. The volume of water filtered per minute was determined on the basis of this equation.The difference between the exponents for weight in the two kinds of feeding can be explained by the probability that when food is abundant filtering rate varies largely with area of mouth opening whereas particulate feeding rate varies largely with capacity.From the filtering rates determined in this study and estimates of filter food concentration in the sea it is hypothesized thatE.mordaxcannot obtain its daily nutritional requirement by indiscriminate filtering alone.

ISSN:0706-652X    

DOI:10.1139/f69-053

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Cod 5–90 cm long in captivity used sight to detect food in midwater. Movement of food stimulated feeding but was not essential when feeding on familiar foods. Adult cod could detect and capture falling food down to 2 mm in diameter. Large pieces of food on the bottom were found by sight but smaller pieces were taken after being detected by taste buds on the trailing barbel and pelvic fin rays. Cod were able to detect odours from many live, intact algae, invertebrates, and fish. Food below gravel or stones was located by smell and uncovered by carrying away gravel in the mouth or by rolling stones aside with the head. Food covered by sand was not found. Some live food was captured in the dark. Cod groups fed more effectively than single cod as food deeply buried was uncovered by several fish digging in the same place; food too large for one fish was pulled apart between fish and feeding behaviour by one fish attracted others to the vicinity of food. Thus shoaling of cod may be advantageous to the species by enabling more food to be obtained from a given area.Larval cod reared from eggs first fed 4 days after hatching. Moving particles were followed by eye movements and captured by swimming forward and snapping if the particles moved in front of the head. Eight days after hatching the cod larvae began to feed on fine stationary particles by removing them from the respiratory water flow.

ISSN:0706-652X    

DOI:10.1139/f69-054

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

A detailed study of retinal structure in 20 pelagic and demersal species of fish indicates that valid correlations exist among the photic environment, activity of the fish, and its visual apparatus. Generally, the relative abundance of rods is inversely proportional to that of the cones. This relationship exists inter-specifically in the same retinal region and intra-specifically in different parts of the same retina. The topographical specialization of cones, or formation of a retinal area, is high in active pelagic species (Clupea,Alosa), less in sluggish demersal fish, and absent in the shore fishTautogolabruswhere a specific ocular behavior compensates. The resolving power of the retinal area is high in pelagic and shore fish, but is lower in demersal species. The distribution of the cone types within a retina suggests that photic sensitivity increases from single to quadruple cones. Cone arrangements are more refined in active species likely to detect fast-moving preys. Inter- and intra-specifically, the development of the inner retinal layers parallels that of the cones. The functional importance of the resolving power appears to rely heavily on the extent of summation at the bipolar and ganglion cell layer level. The cone/rod and single/double cone ratios are proportional to the abundance of bipolar neurons in the species examined.

ISSN:0706-652X    

DOI:10.1139/f69-055

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Bacteriophages forAeromonas salmonicidawere isolated from water and mud samples taken from 13 of 19 trout hatcheries and ponds examined in southern Ontario. Nine of the 13 locations were known to have histories of furunculosis disease. The bacteriophages studied formed three serological groups and two distinct morphological types. Phages of serological groups I and II possessed similar morphology; those of group III resembled the coli T-even phages. All possessed complex symmetry consisting of a head and tail with a contractile tail sheath. Latent periods of the phages ranged from 35 to 95 min and average burst sizes from 21 to 193. A group I phage and a group III phage hadvalues of 351 and 1000, respectively.

ISSN:0706-652X    

DOI:10.1139/f69-056

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

The purpose of this study was to test the reliability of the scale method for determining the age of white suckers. To do so, an alternative method of "aging" was explored, using sections cut from the first four rays of the pectoral fin. Two hundred and fifty white suckers were tagged, and a piece of one pectoral fin was removed before they were released. A year later, 25 were recaptured, and the rays of the remaining pectoral fin were aged. Of the recaptures, 22 showed clearly the addition of one annulus.Having confirmed the fin-ray method, the age of another 157 suckers was determined by scales and fin rays and compared. The results indicated the scale method was reliable, in this population, until the fish reach an age of 5 years. Beyond 5 years there was not close agreement between scale and fin ages. After 8 years, age as determined by scales was invariably less than from fin rays, and sometimes was in error by as much as 5 years.

ISSN:0706-652X    

DOI:10.1139/f69-057

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

In freshwater eels there is a significant correlation between glomerular filtration rates (GFR) and urine flow rates suggesting that changes in GFR rather than tubular water reabsorption lead to the major adjustments in urine flow rates accompanying changes in environmental salinity.Removal of the corpuscles of Stannius was not followed by a significant change in GFR indicating that an adequate (normal) effective filtration pressure is independent of a corpuscular pressor substance.In 8 of 17 Stanniectomised eels urine flow rates exceeded GFR demonstrating that, under these experimental conditions, eel renal tubules secrete water.Multiple tissue electrolyte changes followed Stanniectomy; the 75% increase in the plasma calcium concentration is of particular interest. This increase was probably due to a reduction in the net rate of calcium deposition in bone and not to a change in the renal handling of calcium.

ISSN:0706-652X    

DOI:10.1139/f69-058

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

The magnitude of the variance components in the estimation of the potential egg deposition of sockeye salmon escapements to the Kvichak District, Bristol Bay, Alaska, was determined from data collected from 1957 to 1966. The greatest variance component was caused by estimation of the escapement followed by the variance due to estimation of the ratio of females in the escapement. Estimation of the average fecundity added the least variance.

ISSN:0706-652X    

DOI:10.1139/f69-059

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

The methodology of age determination from scales of chum salmon (Oncorhynchus keta) is reviewed. Scales from chum salmon caught in the North Pacific Ocean and streams of North America were studied. Most annuli are of two main types: a poorly formed circulus usually "cut over" by the first circulus of new growth, and what appears to be a normal circulus in the annual ring. The annulus of type 1 may be independent of the annual ring. Annuli may be at the anterior or posterior margins of the annual ring, or within it. Direct evidence that annuli are recognizable age indices was obtained from scales of marked fish.An average of 98% of the age determinations by three scale readers agreed with the known age of the fish. The time of annulus formation or start of new growth extends from as early as March to the end of June and possibly to the end of July. The annual ring begins to form near the end of the season (as early as August) or when new growth occurs in the spring or summer. Sometimes an annual ring is not formed. Scales taken from various parts of the body had the same number of annuli.

ISSN:0706-652X    

DOI:10.1139/f69-060

出版商:NRC Research Press    

年代:1969

数据来源: NRC