摘要:

When artificial fertilizers were added to unstratified, soft-water Crecy Lake (20 ha), New Brunswick, in three years (1946, 1951, and 1959), the lake was sufficiently self-regulatory that the artificial enrichments had only a temporary effect on organic production. The induced eutrophication proved largely reversible, with minor evidence of hastened senescence of the lake over an 18-year period. Each fertilization provided 210 ppb (parts per billion) of nitrogen (N), 390 ppb of phosphorus (P), and 270 ppb of potassium (K) to the water if the fertilizers were equally distributed throughout the lake.The highest concentrations of total P, determined daily after the fertilizations in 1951 and 1959, were 220 ppb after 2 days and 192 ppb after 1 day, respectively. The concentration of inorganic P declined rapidly from about 150 ppb the day after the fertilizations in 1951 and 1959 to < 10 ppb at a percentage loss per day of 5.5. Concentrations of organic P were highest 5 (80 ppb, 1951) and 8 (43 ppb, 1959) days after the fertilizations and declined to equilibration above prefertilization values for 3–4 months, and then to prefertilization values during the next years. Phosphorus lost in the drainage from the lake, assessed only in 1951 and 1959, was equivalent in these years to 8.5 and 12% of the amounts added in the fertilizers.Limited observations indicated an increase of nitrate N in the water immediately after fertilization, but then a rapid loss. Deficits in dissolved oxygen were greatest under ice in the winters immediately after algal blooms induced by the fertilizers, but were serious in only about 30% of the volume of the lake. Specific conductance of the water exhibited minor change with fertilization.Pronounced algal blooms, not previously recorded for the lake, followed each fertilization. Years of fertilization, and the next, were marked by blooms ofAnabaena. Intensified growth ofSpirogyrausually followed closely the blooms ofAnabaena. In the 3rd year after fertilization algal growth was weak, at prefertilization densities. During blooms ofAnabaenathe numbers of zooplankters and bottom organisms, and growth of submerged, rooted aquatic vegetation, decreased. Zooplankton and bottom fauna were most abundant 2–4 years after fertilizations. Of the rotifers, three out of eight species became abundant. Of the planktonic microcrustaceans,Leptodiaptomuswas always the most numerous;DiaphanosomaandDaphniawere more numerous after the last fertilization (1959) than they were earlier. Among the bottom organisms,Hyalella, chironomids,Amnicola, and sphaeriids increased most in abundance after the fertilizations.

ISSN:0706-652X    

DOI:10.1139/f69-297

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Data collected from the fishery off the southwest coast of Newfoundland indicated a decrease in the proportions of larger and older cod in ICNAF Division 3Pn in recent years. Changes in total mortality rates in 3Pn and on Burgeo Bank have been attributed to fluctuations in total landings and effort. Decreased growth rates for the younger cod and increased followed by decreased growth for the older cod were attributed to increased food supply superimposed on decreased bottom temperatures. Cod from Burgeo Bank grow faster than those from 3Pn. Sizes caught by various types of inshore boats were similar but larger fish were caught in deeper water, in eastern rather than western localities, and in the latter part of the season. Peak spawning occurs in May. Males were predominant in longline catches and matured at an earlier age and smaller size than females. Fish in the 3Pn area matured earlier and at a smaller size than Burgeo Bank fish. Vertebral averages at different localities in the area were similar but averages have decreased in recent years. Limited data on weights and fecundity are presented. Results are discussed in light of the separation of West Newfoundland and Burgeo Bank stocks.

ISSN:0706-652X    

DOI:10.1139/f69-298

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Microbiological investigation was carried out in the waters of the Strait of Georgia during the winter to study the occurrence of heterotrophic microorganisms in relation to other particulate organic materials, including plankton and detritus. High microbial activity was measured in the euphotic zone, where marine bacteria and allied microorganisms were chiefly found on the particulate matter having diameter less than 25 μ. Their standing crop was estimated by different methods to be between 40 and 3000 mg C/m2and some of this was consumed by the zooplankton, which were found to have concentrated the bacteria by a factor of around 105. Only the highest levels of microbial production were estimated to be sufficient for the growth of zooplankton and generally the bacterial activity was only sufficient to support a subsistence level of life for marine copepods in the Strait of Georgia.

ISSN:0706-652X    

DOI:10.1139/f69-299

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

A new test is described for judging the iced-storage age of unspoiled gutted haddock, from early loss of quality to the first gross signs of spoilage. The test is a measure of the changing properties of alpha-glycerophosphate dehydrogenase in tissue fluid with time after death, and is interpreted as an indication of leaching of tissue during the first 7 days of storage. Such functional changes in an enzyme system are a particularly sensitive criterion of freshness in fish during the first 4 or 5 days of iced storage.

ISSN:0706-652X    

DOI:10.1139/f69-300

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

In western North America there are populations ofGasterosteusin which the male nuptial colour is a deep black rather than the normal bright red. Such black populations are usually allopatric to red populations, but in some areas the two forms occur in adjacent sympatry.The difference in male nuptial colour and a number of other morphological and physiological traits reflect genetic differences between black and red populations. Male nuptial colour functions as a partial isolating mechanism. Mate selection experiments indicate that females from red populations rarely accept a black male when they have a choice between a red or black male. Females from allopatric black populations also show a preference for red males, but females from black populations immediately upstream from a hybrid zone appear to mate randomly. The significant difference in mate preference between allopatric and sympatric populations of black females is evidence for the reinforcement of male colour as an isolating mechanism. The selective mechanism reinforcing colour as an isolating mechanism is hybrid inferiority due to genetic incompatibility and aberrant behaviour in hybrid males.A hypothesis is presented that persistent differential predation by an endemic predator (Novumbra) on the young concentrated near the male nest site was the selective force responsible for the evolution of the black genotype. Experiments demonstrate thatNovumbrais differentially attracted to red males when given a choice between red and black males, and that the young of black sticklebacks possess an innate behavioural response toNovumbrathat makes them significantly less vulnerable to predation byNovumbra.

ISSN:0706-652X    

DOI:10.1139/f69-301

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

The specific activity of liver glucose 6-phosphate dehydrogenase in yearling rainbow trout remained unchanged when the fish were starved for periods as long as 8 weeks and when starved animals were fed diets of various compositions. Injection of insulin concurrently with refeeding also failed to alter the specific activity of the enzyme in trout. The absence of a dietary or insulin influence on the teleost enzyme system is to be contrasted with studies in mammals in which the activity of hepatic glucose 6-P dehydrogenase was markedly stimulated after refeeding starved animals or injection of insulin.Ingestion of the pesticide DDT by juvenile coho salmon or adult rainbow trout also had no effect on the specific activity of liver glucose 6-P dehydrogenase and DDT failed to inhibit the rainbow trout enzyme in vitro. These results also differ considerably from those found in higher animals.These results suggest that the glucose 6-P dehydrogenase enzyme in teleosts may be under a different type of regulatory control from that found in mammals.

ISSN:0706-652X    

DOI:10.1139/f69-302

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Fillets of flounder (Hippoglossoides platessoides) and cod (Gadus morhua) produced in two commercial plants from uncut fish that had been frozen in blocks at sea, were free or nearly so of faecal coliforms and generally contained fewer indicator bacteria (all organisms in the coliform group; faecal coliforms) than fillets produced in the same plant from fish iced at sea. Coliforms were found in relatively small numbers on most fillets of thawed fish sampled on the conveyor leading from the mechanical skinner, on similarly prepared fillets sampled after trimming and portioning, and on fillets prepared from fish iced at sea and sampled immediately after skinning. The total plate count on the fillets of thawed fish at the point of trimming and portioning was small, suggesting that the fish frozen at sea carried a relatively low count of fish-spoiling organisms at time of freezing and thawing.The results show that in processing blocks of gutted or gutted and headed fish it is practical to thaw in an immersion thawer at a temperature of 13–20 C while changing the water only infrequently, say every 12 hr, and to employ thawing runs of about 24 hr duration. During this time as many as five tankfuls of fish may be thawed. It is practical also to hold the fish thawed under these conditions in chilled potable water or in crushed ice for 1 or 2 days prior to processing.It was shown that the sanitary aspects of the process can be assessed advantageously by observing the sanitary quality of the fillets, rather than that of the thawing water. The suitability of the method appeared to depend upon efficient washing of the thawed fish before it was put in buffer storage, or before it was filleted, or both. In one of the two plants sampled, large flumes were used and were satisfactory for delivering thawed, washed fish of high bacteriological and sanitary quality from buffer storage to the processing line. Here total plate and coliform counts either increased slightly or decreased slightly with prolonged use of the thawing water and of the boards used in cutting the fillets.

ISSN:0706-652X    

DOI:10.1139/f69-303

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

The response of rainbow trout (Salmo gairdneriRichardson) to overhead light changed with the growth of the fish. No response was evident until the age of 7 months, after which the response became more pronounced with age. Trout exhibited a significant preference for the darkest chamber when given a choice of five intensities of artificial light. Minimum light threshold for 10-month-old fish was between 0.01 and 0.005 lux. However, 24-month-old fish had a lower level of light threshold between 0.005 and 0.001 lux.

ISSN:0706-652X    

DOI:10.1139/f69-304

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Evidence is given that the average daily rations (R) and fortnightly growth increments (ΔW) of six weight groups ofPleuronectes platessafed onMytilus edulisare related as in the power equation ±(ΔW−ΔWm) = ±b(|R–Rm|)B. Rmis the daily ration associated with the growth increment (ΔWm) at maximum growth efficiency;band B are parameters. The power B has a mean value of about 0.5 and shows significant deviations from the mean especially in the case of smaller fish.

ISSN:0706-652X    

DOI:10.1139/f69-305

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Ovarian stromal fibrosis occurred in four Atlantic cod (Gadus morhuaL.) from the northeastern Gulf of St. Lawrence (49°07′N, 59°18′W) and off Fox Harbour, Labrador (52°18′N, 55°52′W), with accompanying cystic lesions in two specimens.Externally the ovaries varied. Specimen 1 (115 cm fork length, age 18 years) possessed clear areas (0.5–1.5 mm) where the underlying stroma was relatively thin. Specimen 2 (107 cm, 19 years) possessed scattered cream or yellow nodules (< 1 mm) and coalesced nodules (1.5–2.0 mm). Specimen 3 (118 cm, 19 years) had many colourless fluid-filled cysts (1.5–2.0 mm) and a few larger cysts (5.0 × 7.5–7.0 × 12.0 mm), the latter confined to the tapering posterior regions of the ovary. Specimen 4 (99 cm, 16 years) possessed large (up to 8 mm) multilocular cysts anteriorly.Stromal fibrosis occurred to varying degrees in each specimen, containing predominantly fibrinoid as identified by Mallory's PAH, Weigert's fibrin test, and retention of a PAS-positive reaction after incubation in alkaline trypsin. Widespread degeneration of ovigerous lamellae occurred in specimens 3 and 4.The condition of specimens 3 and 4 suggests involutional ovarian stromal fibrosis, but the endocrine studies necessary to confirm this opinion were not performed.

ISSN:0706-652X    

DOI:10.1139/f69-306

出版商:NRC Research Press    

年代:1969

数据来源: NRC