摘要:

During a period of eight months, 850 haddock were taken from a trawler from the Nova Scotian and Grand Banks. Immediately after landing, the fish were filleted and the fillets were examined organoleptically and tested for pH and trimethylamine.The results indicate a rather close correlation between the development of early spoilage odours and the increase of trimethylamine. One marked exception was the development of "bilgy" odours which can become very offensive without an increase in the trimethylamine content of the muscle.Sixty-five per cent of the fillets without perceptible spoilage odours had trimethylamine values of less than 1 mg. per 100 g.; 83 per cent had values of less than 1.5 mg., 92.5 per cent of less than 2 mg.; only 0.5 per cent had trimethylamine values of between 3 and 4 mg. and none above that level. Conversely, only 10.5 per cent of the "smelly" fish had trimethylamine values below 1 mg.; 89.5 per cent had values above 1.0 mg., and 66.5 per cent above the 1.5-mg. level. For the purpose of grading freshly cut haddock fillets, the following standards are suggested: trimethylamine values of 0 to 1 mg. per 100 g.–fresh; 1 to 5 mg.–doubtful or spoiling; above 5 mg.–spoiled.In spite of its usefulness as a measure of spoilage, it seems very unlikely that trimethylamine contributes to the early spoilage odours that develop in haddock muscle before the pH reaches 6.9.The pH of the homogenized muscle is not a good indication of the extent of deterioration that takes place in the earlier stages of spoilage of these fish.

ISSN:0706-652X    

DOI:10.1139/f55-019

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

The distribution of salinity, temperature and water transparency observed in the Miramichi estuary in 1950 and 1951 is correlated with the amount of precipitation, river discharge, wind velocity and other physical variables. Assuming complete mixing, the water exchange with the Gulf of St. Lawrence during a complete tidal cycle would be 15%. The residual or non-tidal circulation, resulting chiefly from river discharge, consists essentially of a seaward moving layer of drift within ten feet of the surface and a landward moving layer below that depth.

ISSN:0706-652X    

DOI:10.1139/f55-020

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

A small-scale field experiment was conducted to investigate the migration of Pacific salmon fry through an impounded water basin, 2.4 acres in area. Pink, chum, coho, spring and sockeye fry were released at the upstream end. During nine days of operating a trap placed below the outlet dam, only pink and chum fry appeared. One-quarter of the total of these latter species moved through the impoundment and were recaptured. The migration of the fry was mainly confined to a period 11/2 hours after sunset to 11/2 hours before sunrise. The rate of migration of fry through the impoundment differed significantly from the movement of floats also released above the basin.

ISSN:0706-652X    

DOI:10.1139/f55-021

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

The seaward migration of pink and chum salmon fry takes place at night. Strong light is avoided. In pink salmon negative rheotaxis (swimming with a current) is strongly developed and migration is not primarily effected by random swimming and passive displacement. Downstream movement is mainly at or close to the surface. In slack water vertical distribution is more uniform. In the shortest streams examined, each night's migrants appeared to reach the sea before daybreak. In a longer stream, fry were seen to bury themselves at the onset of daylight. After being held in fresh water for an undetermined period, fry show positive rheotaxis and schooling behaviour and no longer avoid light. Behaviour of fry after reaching the sea also differs from that shown during actual migration. Changes in behaviour may coincide with commencement of feeding.

ISSN:0706-652X    

DOI:10.1139/f55-022

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

A comparison of recent bottom temperatures on the Scotian Shelf with those observed in the period 1934 to 1939 shows that, in general, these temperatures have been higher by from one to three Centigrade degrees in the more recent period. The change has been due to the variation in the intermediate layer which was both colder and of greater thickness during the early period.

ISSN:0706-652X    

DOI:10.1139/f55-023

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

Samples of trout were exposed to flows of water containing constant low concentrations of oxygen (produced by equilibrating aerated water with nitrogen). At 9°–10 °C. minimum tolerance levels were defined by determining the lowest oxygen level permitting survival of 5%, 50% and 95% of the fish for a period of 5,000 minutes. Median resistance times for samples of fish exposed to lethal levels of oxygen were also determined. Within their first year, most trout reared in aerated water could withstand oxygen concentrations down to 1.9 mg.O2/1. The 50% tolerance level was 1.75 mg.O2/1. Most fish died at 1.5 mg.O2/1. Acclimation to low (but not lethal) oxygen levels occurred; for a drop of 1.0 mg.O2/1. in environmental oxygen concentration, the tolerance level decreased by approximately 0.09 mg.O2/1. and resistance times at given lethal levels increased up to five-fold. By acclimations trout could exist at 1.05 mg.O2/1. without direct lethal effects occurring. Between 20 and 33 hours were required for the fish to acclimate to a change of 1.0 mg. per liter in the oxygen concentration of the environment. Acclimation to low levels of oxygen was accompanied by an apparent increase in the ability of the animals to remove oxygen at low environmental oxygen concentrations, suggesting a physiological mechanism similar to that involved in acclimation of mammals to low oxygen. The tolerance levels of small fish were similar to those of large fish at similar acclimation levels, but small fish died more quickly than large fish when exposed to lethal concentrations.

ISSN:0706-652X    

DOI:10.1139/f55-024

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

A regression analysis, which is based on time changes in the ratio of the number of marked fish in the daily catch to the total daily catch, was used to estimate initial population size. This method eliminates overestimation caused by recruitment.

ISSN:0706-652X    

DOI:10.1139/f55-025

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

The general history of the Skeena River commercial salmon fishery is presented from 1877 to 1948. The changes in fishing areas, seasons and fishing methods are described, together with the trends in the catches obtained. The most accurate data pertain to the important sockeye salmon gill-net fishery. The sockeye catch attained a maximum of 187,000 cases in 1910 and since then has declined to a minimum of 28,000 cases in 1933 and 1943. In recent years the catches have tended to level off. The pink salmon catches declined markedly after 1930. The chum catches also appear to have declined in recent years. Whether or not the spring and coho salmon catches have declined is not known. The size of the sockeye catch appears to be the best available measure of the relative size of the population. An analysis of the age cycles in the catch of sockeye and pink salmon did not reveal a practical basis for prediction. Some possible changes in the fishing regulations are discussed and the need for more data on the fluctuations in the size of the stocks during the fresh water phase is stressed.

ISSN:0706-652X    

DOI:10.1139/f55-026

出版商:NRC Research Press    

年代:1955

数据来源: NRC