摘要:

Experiments are reported on the influence of nearly constant dissolved oxygen concentrations, both below and above the air-saturation level, and of wide diurnal fluctuations of oxygen concentration on the appetite, growth, and food conversion efficiency of juvenile largemouth bass,Micropterus salmoides(Lacépède). The experimental apparatus used was designed to provide constant flows of water at 26 C and with controlled oxygen content through 12-gal (45-liter) bottles each containing 10 test fish. The fish were fed unrestricted rations of small, live earthworms throughout the six experiments, whose duration was usually 15 days.The growth rates and food consumption rates of the bass increased markedly with increase of the constant oxygen concentrations to levels near the air-saturation level, and declined with further increase of oxygen concentrations. Gross food conversion efficiencies were considerably reduced only at concentrations well below 4 mg/liter.The growth of bass subjected alternately to low and higher oxygen concentrations for either equal or unequal portions of each 24-hr day was markedly impaired. It was almost always less than that which presumably would have occurred had the fish been held at a constant concentration equal to the mean, either arithmetic or geometric, of the higher and lower concentrations to which the fish had been exposed.

ISSN:0706-652X    

DOI:10.1139/f67-043

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Reproductive isolation appeared to be complete between pumpkinseeds (Lepomis gibbosus) and bluegills (L.macrochirus) when equal numbers (1:1 sex ratio) were stocked in each of two similar ponds near London, Ontario, and observed during the breeding seasons of 1964 and 1965. Ethological isolation, through visual recognition of potential conspecific mates, was probably the major barrier to hybridization. Interspecific courtship and attempted spawning were not seen; intraspecific courtship and spawning were frequently observed. No clearly identifiable hybrids were found among large numbers of yearling and 2-year-old offspring collected in both ponds in 1965 and 1966.Pumpkinseeds began nesting about 3 weeks before bluegills, but spawning by the two species broadly overlapped in time both years. Individual pumpkinseeds occupied nests for an average of 18.5 days; bluegills for 8.7 days. Duration of pumpkinseed nest occupancy appeared to vary directly with surface water temperature, whether eggs or fry were in the nests or not, whereas bluegills tended to remain on nests containing eggs or fry, regardless of temperature fluctuations. Bluegills nested in deeper water and further from shore than pumpkinseeds, and bluegills tended to nest in colonies whereas pumpkinseeds did not. Interspecific differences were not found in nest site selection with respect to substrate or vegetation.

ISSN:0706-652X    

DOI:10.1139/f67-044

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

The morphology ofPhrixocephalus cincinnatusWilson, 1908 (Copepoda: Lernaeoceridae) is described and discussed, with special reference to the structure of the antennae, hitherto almost unknown. Mention is also made of the mode of attachment and of its possible effect on the host.

ISSN:0706-652X    

DOI:10.1139/f67-045

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Pacific coast dogfish (Squalus suckleyi) were skinned, frozen, glazed, and stored at −5, −10, −20, and −30 C to determine the extent of oxidative rancidity, colour change, protein denaturation, and lipid hydrolysis during storage. Belly flaps from dogfish carcasses were tested under similar conditions. Discoloration of the red outer muscle of carcasses was the initial significant change in quality. Initial odour and flavour changes in defrosted carcasses were detected after 22 and 70 days storage at −10 and −20 C respectively; no significant changes were evident in carcasses after 180 days storage at −30 C. Slight fading of the pink colour of belly flaps was observed after storage for 50 days at −20 C and for 160 days at −30 C. A slight acidic type flavour was detected in belly flaps after 99 days storage at −20 C.There was a slight relationship between the extent of protein denaturation and lipid hydrolysis in dogfish muscle during frozen storage.

ISSN:0706-652X    

DOI:10.1139/f67-046

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

The positions of luminous organs and tissues are documented for all known bioluminescent families of fishes. The majority of families, species, and individuals possess photophores only or mainly on the ventral half (as opposed to the dorsal half) of the body. The position and in some cases also the photophore structure tend to direct the emitted light downwards. Review of the previously suggested functions of luminescence and a new one (proposing light organs may function in the spacing out of midwater fish in the absence of marks for fixing territories) suggests that these functions are not related to the ventral predominance of luminescence. Photophores functioning as lures for prey and as headlights do not appear to follow the general tendency for ventral positioning of bioluminescence.Study of the two previously proposed theories on ventral predominance of luminescence, the reflector theory and the "counter-shading" or disruptive illumination theory, shows that there are some cases which these theories do not explain; these two theories apply only during the day. A third theory is developed which suggests that the larger numbers of predators in upper waters would select for fishes with ventrally directed nocturnal luminescence as this would subject them to less predation. Fishespossessphotophores for a number of reasons, but they areplacedventrally because this results in decreased predation. Some counter-strategies are discussed, showing how fishes have coped with certain problems created by bioluminescence.

ISSN:0706-652X    

DOI:10.1139/f67-047

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Tanquary Fjord is ice-covered for a large part of the summer and hence very unproductive. The zooplankton showed variation between the years 1963 and 1964 both in abundance and in species composition, suggesting an unstable system. Development rates and breeding cycles of the calanoid copepods were indicated by the numbers in the various developmental stages. Two forms ofPseudocalanus, differing in the relation of urosome to cephalothorax length, were found. It is unknown whether the two forms are reproductively isolated. The dominant form has a biennial life cycle.Microcalanus pygmaeusappeared to breed biennially. The speciesCalanus glacialisandC.hyperboreuswere shown to be opportunistic breeders; they developed to maturity over a period of several years.

ISSN:0706-652X    

DOI:10.1139/f67-048

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Feeding of the pink shrimp,Pandalus montagui, took place mainly in daylight at low slack water. There was relatively little feeding at low slack water at night, and almost no feeding at other times. Sand grains were ingested with the food and it was possible to identify areas where feeding could have occurred by comparing grain-size distributions of material from the stomachs with those of the bottom deposits. It was possible to show, by fishing in selected areas and by considering patterns of tidal flow, that feeding was restricted to a small area near the mouth of the River Crouch, and thatP.montaguimigrated from this area with the flood tide and returned to it on the ebb.

ISSN:0706-652X    

DOI:10.1139/f67-049

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Annual concentrations of zooplankton off California varied directly, and concentrations in the western Bering Sea varied indirectly with calculated southerly components of Ekman transport in the previous year at 50°N,140°W. This point is in the area in which surface subarctic water and the deeper currents divide north and south. The underlying geostrophic flow requires approximately 1 year to reach each downstream sampling area. Summer concentrations of zooplankton at Ocean Station P, 50°N,145°W, varied with southerly and westerly components at 50°N,160°W during the previous winter. Fifty to sixty per cent of the variance of the annual concentration in zooplankton appears to be due to advection of surface water.

ISSN:0706-652X    

DOI:10.1139/f67-050

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Spores ofClostridium botulinumtype E germinated rapidly under suitably defined conditions ofpH, temperature, and nutrient concentration. The influence of these factors on the rate of germination is presented graphically on the basis of germination proceeding according to a first-order kinetic equation. The effect of agents associated with food preservation on the germination rate demonstrates the value of a rapid germination technique for screening inhibitors of spore germination and outgrowth. The kinetic data are discussed on the basis of the current knowledge of spore activation.

ISSN:0706-652X    

DOI:10.1139/f67-051

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

The seasonal variations in lipid content and general "condition" of cod,Gadus morhuaL., from an inshore population have been determined.Four female and four male fish were chosen from 20 live cod brought in monthly from Terence Bay, Halifax County, Nova Scotia, the fish were pooled and the lipid content determined on the flesh, livers, and gonads. The flesh lipids varied from 0.57% to 0.74% and the oil content of the livers from 15% to 75%.The general "condition" of the fish as expressed by, the liver condition by, and the fat content of the liver all showed seasonal variation with maxima in the fall and minima in the spring. KFvaried from 0.79 to 1.05 and KLfrom 1.0 to 4.5. No seasonal variation in the amount of flesh lipids could be detected.

ISSN:0706-652X    

DOI:10.1139/f67-052

出版商:NRC Research Press    

年代:1967

数据来源: NRC