摘要:

Using a manometric technique an acetylcholinesterase (EC 3.1.1.7, acetylcholine acetyl-hydrolase) was demonstrated in brain tissue from the bluegill,Lepomis macrochirusRafinesque, and the channel catfish,Ictalurus punctatus(Walbaum). The activities were 19 and 37 μmoles acetylcholine hydrolyzed/milligram protein per hour for the bluegill and channel catfish enzymes, respectively. The optimum substrate concentration for the hydrolysis of acetylcholine was 10 mMfor the enzymes from both species. Generally, the catfish acetylcholinesterase was somewhat more susceptible than the bluegill to the inhibitors tested; however, the bluegill enzyme was more susceptible to inhibition by malathion and malaoxon.

ISSN:0706-652X    

DOI:10.1139/f68-059

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Studies carried out in Aburatsubo Inlet (35°09′N, 139°37′E) showed that generally during the spring the dark assimilation of carbon dioxide was a large fraction of the total carbon dioxide assimilated. During the rest of the year photosynthesis accounted for most of the production of the water column, but dark assimilation was sometimes appreciable in the sediments. Production generally exceeded mineralization, indicating a net gain of organic matter either in the sediments or in adjoining water masses.

ISSN:0706-652X    

DOI:10.1139/f68-060

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

From 1 to 50 ppm of 10 different heavy metal ions were added to blended muscle taken from freshly killed cod, haddock, flounders, redfish, herring, mackerel, scallops, and lobster, and stored for 24 hr at 0 C. The resulting rancidities were determined by thiobarbituric acid (TBA) values and odours. With some exceptions, Fe++, V++, and Cu++were the most active catalysts. Fe++was always more effective than Fe+++. Cd++, Co++, and Zn+produced randicity with the fatty species but not with any of the other species that were tested. Ni++, Cr++, Ce++, and Mn++did not accelerate rancidity in any of the muscles. There was considerable difference in the relative susceptibility of muscle from different species to rancidity induced by specific metals. During frozen storage, changes in fish muscle took place that rendered it less susceptible to subsequent metal-induced rancidities.

ISSN:0706-652X    

DOI:10.1139/f68-061

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Growth in length and weight of round whitefish was similar in two localities in Ungava, northern Quebec. The pattern of growth, however, differed from those reported previously for round whitefish from the Great Lakes. Round whitefish from Ungava are slow growing and approach their maximum size at a constant growth rate, whereas those from the Great Lakes approach their upper size limit rapidly within the first 3 years and thereafter growth is slow. The maturing age was greater for both Ungava males and females (4+ and 3+ years respectively for the earliest specimens) than for round whitefish from the Great Lakes. Though round whitefish are abundant in the Ungava region, they are of no commercial interest because of their slow growth and small average size.

ISSN:0706-652X    

DOI:10.1139/f68-062

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The species composition of fish in the Great Lakes has undergone continual change since the earliest records. Some changes were caused by enrichment of the environment, but others primarily by an intensive and selective fishery for certain species. Major changes related to the fishery were less frequent before the late 1930's than in recent years and involved few species. Lake sturgeon (Acipenser fulvescens) were overexploited knowingly during the late 1800's because they interfered with fishing for preferred species; sturgeon were greatly reduced in all lakes by the early 1900's. Heavy exploitation accompanied sharp declines of lake herring (Leucichthys artedi) in Lake Erie during the 1920's and lake whitefish (Coregonus clupeaformis) in Lake Huron during the 1930's. A rapid succession of fish species in Lakes Huron, Michigan, and Superior that started about 1940 has been caused by selective predation by the sea lamprey (Petromyzon marinus) on native predatory species, and the resultant shifting emphasis of the fishery and species interaction as various species declined. Lake trout (Salvelinus namaycush) and burbot (Lota lota), the deep-water predators, were depleted first; this favored their prey, the chubs (Leucichthysspp.). The seven species of chubs were influenced differently according to differences in size. Fishing emphasis and predation by sea lampreys were selective for the largest species of chubs as lake trout and burbot declined. A single slow-growing chub, the bloater, was favored and increased, but as the large chubs declined the bloater was exploited by a new trawl fishery. The growth rate and size of the bloater increased, making it more vulnerable to conventional gillnet fishery and lamprey predation. This situation in Lakes Michigan and Huron favored the small alewife (Alosa pseudoharengus) which had recently become established in the upper Great Lakes, and the alewife increased rapidly and dominated the fish stocks of the lakes. The successive collapses of various stocks after periods of stable production may give some indication of their sustainable yield. The sea lamprey is being brought under control in Lakes Superior, Michigan, and Huron; lake trout are being established; and chinook salmon (Oncorhynchus tshawytscha), coho salmon (O.kisutch), kokanee salmon (O.nerka), and the splake, a hybrid of lake trout and brook trout (Salvelinus fontinalis), are being introduced to reestablish a new species balance. Fish stocks are in a state of extreme instability in these lakes. Careful control of stocking programs and fisheries, and coordination of management among the various states of the United States and the province of Canada (Ontario) which manage the fish stocks, will be required to restore and maintain a useful fishery balance.

ISSN:0706-652X    

DOI:10.1139/f68-063

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Infection of the lobsterHomarus americanuswith the bacteriumGaffkya homariinvariably proved fatal. Very small numbers of this pathogen introduced into the hemolymph resulted in septicemia and death, i.e., a dose level as low as approximately five bacteria per lobster at a temperature of 15 C was sufficient to kill 90% of the lobsters in 17 days. The mean time to death was virtually constant, regardless of the dose, indicating a general lack of host defense againstG.homari.Investigation of the interaction ofG.homariwith the defense factors apparent in lobster hemolymph (bactericidal, agglutinin, and phagocytic activities) helped to account for its pathogenicity.Gaffkya homariwas unique among the microorganisms tested in that (1) it was resistant to the agglutinin (s); (2) its growth was stimulated by the hemolymph serum rather than inhibited or unaffected; (3) although it was phagocytized, the bacterium could overcome this effect and multiply in the hemolymph.

ISSN:0706-652X    

DOI:10.1139/f68-064

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Analysis of echo-sounder and sonar records made on Lake Mendota during summer and winter indicated that the schooling behavior of yellow perch,Perca flavescens(Mitchill), changed markedly between the two seasons. The distance separating individuals in schools during summer was less than 1.5–2.0 ft, consequently producing dense traces on the recorder charts which showed no definition of individuals. During winter, however, the fish-to-fish distances often were greater than 1.5–2.0 ft, producing many traces showing the individual fishes in a school. The mean distance between the top and bottom fish in a school during winter was 22.1 ft (6.7 m); in summer only 8.5 ft (2.5 m). High correlations existed between light transmission of the water and school size (r =.77) and between temperature and school size (r = −.89). The possible adaptive significance of this seasonal change in behavior is discussed.

ISSN:0706-652X    

DOI:10.1139/f68-065

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Dawes (1930, J. Marine Biol. Assoc, 17: 103 and 877) gave extensive data on average daily rations and fortnightly growth increments ofPleuronectes platessafed onMytilus edulis. The data are analyzed here in an attempt to formulate a ration and growth increment relationship. Fortnightly growth increments, Δw, were arranged in eight groups according to eight ranges of fish weights. The growth increments in each group, associated with each average daily ration level (R), gave evidence of the normal distribution. Each range of fish weights was characterized by a certain range of daily rations associated with growth increments having homogeneous variance, as well as by a certain daily ration, Rm, associated with maximum growth efficiency. There was evidence that growth increments, of each range of fish weights, were linearly related withsuch that the value of the square root is positive if R > Rmand negative if R < Rm, i.e.,whereaandbare parameters.

ISSN:0706-652X    

DOI:10.1139/f68-066

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Quality assessments, based on organoleptic evaluations and chemical tests, were conducted before and after cold storage, on trap-caught cod (Gadus morhua) which was unfrozen, once-frozen, or twice-frozen. The cod was processed both before and during rigor, after icing or after handling without ice, at various times during the catching season.Lactate determinations andpH measurements on whole fish at killing showed a seasonal variation. There was a correlation between lactate determinations andpH measurements in freshly killed and freshly frozen fillets that had been frozen both before and during rigor. Icing immediately after killing slowed the rate of lactate accumulation.Differences in the state of pre- and in-rigor chilled fish at freezing, as assessed by muscle glycogen, lactate, and reserves of ATP, resulted in differences in texture, thaw-drip, andpH. Patterns in texture may be predicted by the amounts of thaw-drip and thepH measured in the cold-stored pack.Intensity of mealiness and short-grained features in freshly frozen (once) fish was correlated with the level of ATP immediately before cooking. Fillets frozen before rigor toughened very slowly in storage at −23 C and the mealy condition eventually disappeared. Hence, fish downgraded for mealiness at freezing improved or maintained initial overall texture scores during 6 months in storage. Although the panel showed a clear preference for fish frozen pre-rigor, it would be impossible for industry to freeze more than a portion of the landings pre-rigor. To obtain the next best once-frozen product, chilled in-rigor fish should be processed.Double freezing gave the next best product from chilled, prerigor fish. Fish frozen pre-rigor in the "dressed" condition and stored at −23 C, then thawed, processed, and refrozen at 16 weeks, was equal in quality to once-frozen controls. The texture in the twice-frozen material prepared from iced, prerigor frozen fish dropped after a further 10 weeks storage, making it little better than the twice-frozen product of commercial-like handling. A very satisfactory twice-frozen product was obtained also by holding unfilleted blocks of non-iced, gutted fish at −46 C before thawing and refreezing, followed by remaining storage at −23 C. However, such low temperature storage is not within the scope of present commercial operations.With pre- and in-rigor frozen material a correlation was found between thaw-drip andpH, thaw-drip and overall texture (in-rigor freezing only),pH and overall texture values, and betweenpH and toughness. There was also a correlation between extractable protein nitrogen (EPN) values and overall texture scores of fish frozen in various stages of rigor (encountered during unfrozen storage of upwards of 24 hr before processing) but not between EPN and overall acceptability. With twice-frozen fillets prepared from material also handled unfrozen as above, there was significant correlation between EPN values at tasting and overall texture scores and between EPN and overall acceptability scores.Free fatty acid (FFA) values of the trap fish were high and showed no increase as the result of thawing and refreezing or further storage at −23 C or with pre- and in-rigor freezing. Storage at −46 C resulted in less FFA development. There was significant correlation between EPN and FFA values for June-caught once-frozen fish and between FFA values and strictly taste scores for June and July fish but no correlation between FFA and overall texture scores, or in the case of twice-frozen fish of any particular pre-freezing treatment, between FFA and taste, overall texture, or overall acceptability.

ISSN:0706-652X    

DOI:10.1139/f68-067

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The hypothesis that natural mortality rates of pink salmon during early life are generally much larger than during the later period has been tested for 3 brood-years of the Bella Coola River stock using a two-stage marking technique. Average daily losses to the population during the first 40 days are estimated to vary between 2 and 4%, and for the later 410-day period between 0.4 and 0.8%. These rates produce losses amounting to between 59 and 77% of the initial population during the first 40 days. Of the population surviving at 40 days, further losses of between 78 and 95% occurred. The latter losses are considered to be maximum estimates because of bias introduced by catches of unknown magnitude. Thus, although the early mortality is exceeded by the later, the time period is approximately 10 times as long, and the intensity of the mortality rate is much higher during early sea life.

ISSN:0706-652X    

DOI:10.1139/f68-068

出版商:NRC Research Press    

年代:1968

数据来源: NRC