摘要:

An artificial 5-acre (2.0-ha) pond formed on Ellerslie Brook, Prince Edward Island, initially resulted in an increased fishing effort and yield of brook trout to anglers from the stream system — estuary, pond, and stream. The increased effort and catch were not sustained. After 4 years, annual effort and yield of trout by number from the system were not significantly different from the pre-pond period. Length of angled trout and yield by weight declined significantly. Sea-running trout, prized by anglers, were largely eliminated. Only when planted into the estuary did hatchery-reared trout make good contributions to the anglers' catches.

ISSN:0706-652X    

DOI:10.1139/f68-020

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

In mackerel, by the time of initial sampling, adenine nucleotides had been deaminated to inosine monophosphate (IMP) in the ordinary muscle; in the red muscle the degradative sequence was even more advanced, as indicated by high initial levels of inosine. Postmortem rates of degradation of IMP to hypoxanthine through inosine were similar in both types of muscle; at ice temperature the rates were slower than in cod but faster than in swordfish. A delay in icing of 6–8 hr after catching accelerated the gradual decline in eating quality with replacement of the characteristic fresh mackerel flavor by tastelessness. IMP dephosphorylation paralleled development of tastelessness, and spoilage (organoleptic) had developed prior to accumulation of appreciable amounts of hypoxanthine. At higher temperatures, 5–20 C, rates of IMP dephosphorylation, hypoxanthine accumulation, and quality loss were markedly increased. Thawing did not influence subsequent deterioration rates, but ascorbic acid dips delayed darkening of the flesh in the thawed samples.Excellent correlation of taste with both IMP and hypoxanthine content, and with various simple measures of IMP dephosphorylation, was obtained under the various handling conditions investigated, including delayed icing, holding at elevated temperatures, and after thawing. The simple tests — ultraviolet absorption at 248 mμ of a Dowex treated perchloric acid extract, and ratio of ultraviolet absorption of extracts at 251 mμ after Dowex treatment to that before treatment — proved as good indices of progressive quality loss to the unacceptability level as the more complex estimation of IMP or hypoxanthine.

ISSN:0706-652X    

DOI:10.1139/f68-021

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

For estimating populations of trout-perch,Percopsis omiscomaycus(Walbaum), by immersing fish in solutions of stains, Bismarck brown Y was superior to two other stains tested. It was satisfactory for periods of marking up to 1 week. Neutral red indicator can be used in marking experiments of less than 2 days' duration but Nile blue A faded rapidly and is not recommended for use in estimating populations. Using multiple and single census methods of estimating population size, the most reliable estimates of trout-perch greater than 46 mm in length were 711,451 (Schnabel) and 883,148 (Petersen), or in number per acre 1186–1472.

ISSN:0706-652X    

DOI:10.1139/f68-022

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Determinations of dimethyl-β-propiothetin (DMPT) levels are reported for 10 filter-feeding organisms, 1 browsing mollusc, 1 carnivorous mollusc, and 1 crustacean. Mature oysters, scallops, and the pteropodLimacina helicinashowed high (ca. 0.1 mg/g) DMPT levels, mussels showed generally lower levels, and quahogs and a tunicate showed negligible amounts of DMPT. The periwinkle accumulated DMPT only when feeding on an alga rich in DMPT. Retention of DMPT over prolonged periods was studied in the oyster and in mussels.Seasonal variations, year-to-year variations, and variations with locations were studied for oysters and to a limited extent for mussels. The findings are discussed in terms of food availability and feeding habits and indicate that together with tocopherol it may be possible to correlate DMPT levels with the availability of phytoplankters in the food intake or some species. It is suggested that phagocytes may be responsible for prolonged retention of DMPT in oysters.

ISSN:0706-652X    

DOI:10.1139/f68-023

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

In Lake Opinicon, Ontario, the diet of the black crappie,Pomoxis nigromaculatus, undergoes a progressive change from one in which planktonic Crustacea and small-bodied Diptera larvae predominate (in fish of body length from about 60 to 115 mm), to a diet of insect larvae and fish (in fish 160–240 mm). Most food items prove to be midwater forms and the Diptera larvae are almost entirelyChaoborusandProcladius, which are free-swimming in the water column at night.An unusual feature is the prolonged nature of the Cladocera-Copepoda eating phase, which continues into year III and to a body length of about 160 mm. Gill-raker counts showP.nigromaculatusto have a specialized screen with 25–29 rakers on the first arch. In this it differs from cohabiting centrarchids in Lake Opinicon,Ambloplites rupestris,Micropterus salmoides, andLepomis macrochirus, in which the rakers on the first arch number only 8–12. In these species plankton feeding is restricted to the earlier stages.

ISSN:0706-652X    

DOI:10.1139/f68-024

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Trawler-caught cod were frozen before and after rigor mortis in brine (23% NaCI) and between refrigerated plates, thawed in circulating water at 7 C or in a conveyorized microwave oven, then processed into fillets which were packaged, plate-frozen, and stored at −18 C.All samples thawed satisfactorily in circulating water. Some overheating was encountered during thawing in microwaves. But the equipment was not developed sufficiently to permit assessment of the commercial potential of microwave thawing.Examinations of the fillets from the thawed fish for appearance, odor, and texture showed that freezing pre-rigor is preferable to freezing post-rigor and that thawing by means of microwaves is preferable to thawing by means of water. Freezing or thawing methods did not affect thepH of the thawed fillets.Results of organoleptic and chemical tests to determine the changes in quality of the refrozen fillets packaged and stored at −18 C for 12 months indicated that neither the average taste panel scores nor the chemical tests for moisture, total lipid, free fatty acids, and extractable protein nitrogen showed any difference attributable to state of rigor, freezing method, or thawing method. The taste panel slightly preferred the texture of fillets from fish frozen pre-rigor and from fish frozen in brine. Free fatty acids increased sharply as a result of thawing and refreezing, and the rapid increase continued during the first 2 months of frozen storage. Taste panel scores correlated significantly with free fatty acids (1% level) and with extractable protein (5% level).

ISSN:0706-652X    

DOI:10.1139/f68-025

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

This paper redescribes three species of Chondracanthidae (Copepoda) parasitic on the fishes of British Columbia and previously recorded by earlier writers (Chondracanthus irregularis,Ch.pinguis, andCh.gracilis). Two new species are described (Ch.pusillusandAcanthochoniria holocephalarum). Finer structural details of the chondracanthid appendages are illustrated and the taxonomic status of the previously known species is discussed.

ISSN:0706-652X    

DOI:10.1139/f68-026

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Five surveys in the Queen Elizabeth and nearby islands during the summer of 1962 collected 1221 specimens of decapod Crustacea. These decapods comprised 10 species of hippolytid and crangonid shrimps. Sizes and maturity status of specimens indicated variability in adaptation of different species to the low temperature environment. Records of northern distribution of the species in Canada and Greenland are reviewed. Food was mostly detritus and phytobenthos but some species showed preference for foraminiferans or crustaceans.

ISSN:0706-652X    

DOI:10.1139/f68-027

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Non-frozen storage of sperm for several weeks was achieved by the use of buffered protective agents and low temperature. For example, sperm stored with 5% dimethyl sulphoxide at −4.5 C for 28 days gave 81% fertility; use of 5% ethylene glycol allowed storage at −3 C for 38 days, giving 70% fertility. It is suggested how these results may be employed for interspecific mating of salmonids. Attempts to employ glycerol as a protective agent were unsuccessful as were all attempts at freezing sperm.The necessity of providing an adequate air-space in vials used for short-term storage of undiluted sperm of Atlantic salmon is demonstrated.Although a rough correlation between motility of sperm and fertilization is reported, caution in the interpretation of motility as an indication of fertility is suggested.

ISSN:0706-652X    

DOI:10.1139/f68-028

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Bluegills,Lepomis macrochirus, entrained to natural or artificial light–dark cycles, were confined to constant darkness for varying periods up to 42 hr at temperatures in the range 20–25 C. The retinomotor activities were determined from histological preparations. In the first night, the eyes became maximally dark-adapted within 1 or 2 hr. The pigment was contracted to a dense basal band, twin cones extended to the boundary of the pigment, and single cones extended into the pigment. After 2 or 3 hr in darkness, these components began a return toward their light-adapted positions, slowly for 5 or 6 hr, and then rapidly during the last 3 or 4 hr, and came to rest in an intermediate state of adaptation at subjective sunrise. In continuous darkness, the retina exhibited a rudimentary free-running rhythm, and there was some evidence of a 12-hr oscillation within the 24-hr period. The amplitudes of the rhythms ranged in decreasing order from twin cones to single cones to pigment and the extreme amplitudes occurred about 2 hr after sunset and at subjective sunrise. Single cones were always more extended than twin cones and only the rod-shaped particles, not the spheres, of pigment appeared to cycle. By the end of the experiment, the rhythms of cones were slightly damped and the rhythm of the pigment was greatly damped. Rods were not studied.

ISSN:0706-652X    

DOI:10.1139/f68-029

出版商:NRC Research Press    

年代:1968

数据来源: NRC