摘要:

The food and feeding ecology of five species ofGenesin the estuaries of Natal, were investigated from 1978 to 1980. The Kosi system, consisting of an estuary and three main lakes was selected as the main study area due to an abundance ofGenes. Four other estuarine systems were sampled.At Kosi polychaetes were important at the estuary, siphon tips (distal ±5 mm) of the bivalveHiatula lunulatawere most commonly taken in Lakes Makhawulani and Mpungwini, while chironomid larvae were important in Lake Nhlange. Ivlev's electivity test showed thatGenespositively selected bivalve siphon tips when searching for food. The food taken byGenesfrom other estuaries was similar to that at Kosi, although the proportions of the different prey varied. At Kosi between three and five species occurred sympatri‐cally. Resource segregation was through differences in diet and feeding periodicity and a superabundance of food (H. lunulatasiphon tips) during summer and autumn. During winter and spring when food may be limiting, mostGenesleave shelf areas of the Kosi system, onlyG. acinacesremains in large numbers. Little is known of the diet of other fish which feed on benthic invertebrates in Kosi but there is probably little direct competition with Gerreidae, althoughAcanthopagrus berdaandPomadasys commersonnihave been recorded feeding on the siphons of the bivalveSolen corneus, the former in Durban Bay and the latter at Kosi. In areas where the bivalveH. lunulataoccurs it is suggested that Gerreidae have developed optimal foraging techniques which enhance resource partitioni

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04760.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

A systematic survey of motor innervation in the myotomal muscle fibres in several groups of fishes was conducted to observe the extent of dual innervation, a phenomenon found within those myotomal muscle fibres with terminal innervation. It is concluded that the dually innervated myotomal muscle fibre is a primitive vertebrate feature. Furthermore, it is suggested that this particular form of polyneuronal innervation is retained in the course of neural evolution within the homogeneous white myotomal muscle fibre region in these fish groups in order to insure synchrony of firing during sudden, rapid locomotion. The findings are examined in light of current ideas regarding the direct adrenergic innervation in addition to cholinergic innervation of striated muscle fibres.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04761.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Planktonic postlarvae of yellow fin breamAcanthopagrus australiswere found at surf bar entrances to Moreton Bay, a large subtropical estuarine system on the east coast of Australia. The postlarvae occurred from April to September with peak abundance during July to September. Most postlarvae entered the estuary at night during the full moon. They were more abundant on the flood and full tides than on the ebb tide. The transition from planktonic to littoral existence occurs from August to November when the fish are 13‐14 mm in length. Young yellow fin bream in littoral areas reach a modal length in excess of 100 mm after 1 yea

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04762.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The various methods by which chromosomes using lymphocytes, fromSalmo truttaandCyprinus carpio, can be collected, prepared and stained for analysis are described and evaluated.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04763.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

A study has been made of the chemical nature of feeding stimulants for juvenile European eels,Anguilla anguilla. Mixtures of L‐amino acids were stimulatory, while neither the corresponding. D‐amino acids nor the non‐amino acid components were effective. Synergistic effects were observed both between L‐amino acids and between L‐amino acids and non‐amino acid constituents. The results are discussed in the context of results obtained from electrophysiological and behavioural studies with ot

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04764.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The survival and growth of rainbow trout,Salmo gairdneriRichardson, stone loach,Noe‐macheilus barbatulus(L), bullhead,Cottus gobio L., three‐spined stickleback,Gasterosteus aculeatusL., minnow,Phoxinus phoxinus(L), and roach,Rutilus rutilus(L), have been studied in water of three qualities—Birmingham tap water, 50% and 100% settled effluent from filter beds. Predicted toxicities (the sum of the proportions of the 48‐h LC50 of individual poisons to rainbow trout) were compared with the observed toxicity in 50% and 100% effluent. The behaviour of each species offish and the rates of mortality over an exposure period of 210 days are given together with cumulative growth rates (as a percentage of the initial weight). The Mean Percentage Change in Weight (MPW) and Mean Growth Rate (MGR) for each group offish was calculated from the initial mean wet weight and the mean weight of surviving fish at the end of the first and second intervals. The Mean Production Rate (MPR) over the experimental period was also calculated and was used as a holistic measure of the rate of total tissue elaboration or utilization, or loss in biomass due to mortality. The Condition Factor (K) also reported was calculated from the body weight and length and was used to examine (a) the effects of water quality, and (b) the timing and duration of maturation of the gonads. The latter was further used as a measure of the energy status of t

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04765.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

A 3‐year study was made of the soft, acid waters of the Rivers Mawddach, Wen and Gain, which contained copper, zinc and iron from natural outcrops and abandoned mines. Invertebrates, typical of acid to neutral streams, were present but there was no pattern in overall numbers or in biomass between stations. However, the abundance and distribution of Ephemeroptera were related to pH and water hardness although not to copper and zinc. Brown trout,Salmo trutta, were present and there was little difference in rate of growth between stations, whereas biomass and population density varied considerably between stations, being related to water quality such that, where annual median and 95‐percentile of the summed proportions (p) of the threshold LC50 concentrations of copper and zinc to rainbow trout, S.gairdneriwere 0·3 and 0·7 respectively, biomass was half that in the absence of the metals and, where they were 0·6 and 1·3 respectively, no fish would be expected to occur. Low pH was an additional adverse factor at some locations. Salmon,S. salar, failed to populate a tributary where the sum of thep tLC50 values of copper and zinc was 0·45. High aqueous concentrations of copper resulted in elevated concentrations of copper in the liver of trout, especially in older fish, but not in the muscle. Concentrations of zinc in fish liver and muscle were low despite high ambient concen

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04766.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

When reared for a period of 6 months at a temperature of 10°C Arctic charr,Salvelinus alpinus, increased in weight from 18 g to approximately 135 g. Specific growth rates decreased as the fish increased in size and the relationship between size and growth rate could be described by the equation:whereGwis specific growth rate andWis fish weight in grams. Temperature effects upon growth were examined using previously published data. Below the optimum growth temperature, the growth rate of a fish of given size could be predicted using the equation:whereTis the rearing temperature.Rates of growth of Arctic charr were as high as those reported for other salmonid species reared under similar conditions. Preliminary results suggested that growth rates of charr may be lower in salt water than in fresh water

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04767.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

DNA of rodlet cells and erythrocytes from three species of freshwater teleosts,Semotilus atromaculatus atromaculatus, Catostomus commersoniandCyprinus carpio, was stained with the Feulgen reaction and examined by microdensitometry. Rodlet cells showed nuclear DNA content significantly different from erythrocytes of the same species, but the difference was less than a factor of C, assuming that erythrocytes reflect the normal 2C genome of somatic cells. In two species,S. atromaculatusandC. carpio, the rodlet cell nuclei contained less DNA than the erythrocytes; in C.commersonithey contained more. The identity of the rodlet cell is unknown; the results of these experiments lead to the rejection of the hypothesis that rodlet cells and erythrocytes of a species have the same DNA content, i.e. that the rodlet cell is a normal somatic component of fish tissue.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04768.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Ovaries of female capelin,Mallotus villosus villosus(M), from the Barents Sea were sampled at various times of the year and material conserved for morphological examination. The maturity of female capelin, was assessed using low power microscopy for examination of whole oocytes. The diameters of oocytes were measured to give additional information regarding development, and to study the growth rate of the ripening oocytes. A maturity scale for use in the field is described based on the result of low power microscopy. A comparison is made between the‘old’and‘new’maturity scales, and the ease of use of the new scale has been

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04769.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY