摘要:

Patterns of parasitic infections ofSchizothorax intermediusin two water bodies of North Tadjikistan (Central Asia), one with constant temperature during the whole year, the other with normal annual seasonal range of temperature fluctuations, have been studied. It has been shown that in the first water body fluctuations in occurrence of the parasites are insignificant and are not under the influence of water temperature.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03514.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A comparative study has been made of the mucogenic epidermis of the common carp,Cyprinus carpiovar.communis, and the three Indian major carps,Catla catla, Labeo rohitaandCirrhina mrigala: on the basis of epidermis structural organization, these species are easily differentiated.The epithelial cells in the superficial layer, as in most fishes, show secretory activity, evidenced by positive histochemical reactions, which is high inC. carpiovar.communis, moderate inC. catlaand low inL. rohitaandC. mrigala. The epithelial cells in the underlying two or three layers also give positive reactions, though their intensity is relatively weak.The mucous cells in C.carpiovar.communisare distributed in large numbers arranged in several superimposed layers in the outer regions of the epidermis, whereas inC. catlathey are fewer in number and are widely separated in the surface layers as well as in the deeper layers of the epidermis; in both species the mucous cells appear rounded, large, and open on the surface by wide pores. In contrast, inL. rohitaandC. mrigalathe mucous cells are smaller, restricted mainly to the superficial layer, close together in a single row, and open on the surface by narrow pores. The overall density of mucous cells inL. rohitaandC. mrigala, as inC. catla, is much lower than inC. carpiovar.communis.In the epidermis ofC. carpiovar.communisthere are a large number of mucous cells, and the few club cells are restricted to the deeper layers. In contrast, in the epidermis of the three Indian major carp the overall density of the mucous cells is much lower and the club cells are very numerous. It is suggested that the high density of club cells compensates an overall low density of mucous cells as an adaptation for an effective defence mechanism.Increased mucus production in the epidermis of C.carpiovar.communis, as evidenced by a large number of mucous cells in outer regions and high secretory activity of superficial layer epithelial cells, is associated with increased precipitation of mud held in suspension, needed as an adaptation to the species’peculiar bottom‐scooping habits.The varied density of the taste buds in the epidermis of the four carp is associated with their feeding hab

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03515.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The growth pattern of myotomal red, pink and white muscle and its relation to somatic growth inCaranx malabaricusare described. The growth pattern of red muscle was by an increase in fibre number in early size classes (<22 cm f.l.) and thereafter mainly by increase in fibre diameter and partly by increase in fibre number. The growth of pink muscle was mainly by an increase in fibre diameter, but in smaller fish an increase in fibre number was also evident. White muscle growth was mainly by an increase in fibre diameter and partly by increase in fibre numbers in fish<22 cm f.l., but only by an increase in fibre diameter from 22 cm f.l. onwards.Caranx malabaricusis a slow‐to‐moderate growing species and its fibre growth pattern matches with such somatic gro

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03516.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Histological changes in the ovaries of pike from two shallow, adjacent, Scottish lakes are described and related to a macroscopic scale of maturity stages and to changes in gonad weight. There was no evidence of pre‐ovulatory degeneration although occasional residual oocytes were present in spent ovaries. The gonadosomatic index (GSI) was high in males from October to March, and in females it increased through the winter months to a maximum immediately prior to spawning. Maximum ovarian weight was 8.3–9.0% of total body weight compared with only 0.9–1.1% for testes. These GSIs were low compared with other reports for the British Isles, suggesting lower reproductive output. Spawning occurred in the first two weeks of April at a water temperature of 6.0–7.5° C. Fecundity was described from a regression of egg number (F) on fork length (f.l.): log10F= ‐1.51 + 3.33 log10f.l. (cm). Mean egg diameter after preservation varied from 1.1 to 2.4 mm over the size range examined. Males were mature at age 2 at a length of ≥ 27 cm, while females first spawned at age 3 at a length of ≤ 28 cm, although a minority were mature at age 2. The sex ratio was 1.2 males: 1 female at Kinord and 1.4 : 1 at Davan. Greater egg production at Davan, 50 678 ha−1, compared with Kinord, 33 557 ha−1, was due to higher individual fecundity‐at‐age resulting from better growth.Fecundity (19.29 × 103calculated for a pike of 55 cm F.L.), relative fecundity of only 10–24 eggs per gram wet weight of adult, and GSI values were low compared with pike in North America and Eurasia. Food supply may restrict reproductive output of pike in Lochs Kinord and Davan. The abundance ratio of predator: prey is high with the main prey species, perch, present in low numbers, and the only alternative species is eel in thes

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03517.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The technique of X‐ray cinematography was used to study pharyngeal movements inAbramis brama(L.). The theoretical and practical problems in X‐ray cinematography of feeding fish are discussed, as well as criteria for the selection of images suited for detailed measurements.Respiration and filter‐feeding onDaphnia pulex(lengthc. 1 mm) show different gill arch movement patterns in bream. Slits between gill‐arches are kept smaller during filter‐feeding. In addition, during filter‐feeding, this inter‐arch distance decreases considerably in a posterior direction. The hypothesis that particle retention occurs on the slits formed between adjacent gillarches and their gill‐rakers is not supported by the

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03518.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

This paper presents evidence that the size of the nuclei of parenchymal cells of the liver is correlated with the nutritional status of first‐feeding pejerrey larvae,Odontesthes bonariensis(Cuvier et Valenciennes). Kariometry revealed that larvae which successfully began exogenous feeding maintained the large nuclear sizes attained during the period of endogenous feeding. In contrast, nuclei of fasted larvae shrank gradually and lowest values were attained before starvation death. The degree of shrinkage seemed to be dependent on rearing temperature; reduction in nuclear area was faster and more pronounced at higher temperatures. In addition, mean hepatocyte nuclear areas of larger as well as of triploid fish are presented. The results suggest that hepatocyte nuclear size might constitute an alternative indicator for the identification of starving condition in field larval specimen

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03519.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The feeding ecology of whitefish,Coregonus, larvae in oligotrophic Lake Sarnen and eutrophic Lake Hallwil is presented, taking into consideration the size of the prey ingested in relation to the mouth size of larvae and to the availability of zooplankton.When larvae grow from 10 to 16 mm their mouth width increases from 500 to 1000 μm while their gape height, with the mouth open at 45 and 90°, increases from 200 to 400 μm and from 400 to 700 μm, respectively, whichever lake is considered.The differences found in the mean prey width between the two lakes arise in part from the composition of diets, and in part from differences in size of the available prey organisms. Whatever the origin of the larvae and the taxon we consider, larvae seem to ingest the most abundant prey size without selecting the biggest ones available even if, from a mechanical point of view, they would be able to ingest them.Taking into account the generally low density of zooplankton in the uppermost layer of the lake, we conclude that whitefish larvae eat in the manner such as to decrease the cost of prey capture, in terms of energy and time, by choosing the more abundant prey availa

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03520.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Four computational methods for estimating mean fecundity are compared by Monte Carlo simulation. One of the four methods is the simple expedient of estimating fecundity at sample mean length, a method known to be downwardly biassed. The Monte Carlo study shows that the other three methods reduce bias and provide worthwhile efficiency gains. For small samples, the most efficient of the four methods is a ‘bias adjustment’, proposed here, that uses easily calculated sample statistics. For large samples, a numerical integration method has the highest efficiency. The fourth method, a ‘direct summation’ procedure which can be done easily in many statistical or spreadsheet programs, performs well for all sampl

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03521.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A genetic study was carried out on a neotropical fish species to illustrate the refuge theory, whose main principles are summarized. The geographical structure of the anostomid speciesLeporinus fridericiwas analysed in French Guiana and Brazil by horizontal starch gel electrophoresis. Fifteen enzymatic systems corresponding to 21 loci were studied, revealing the following particularities: (1) specimens of fish from six independent coastal rivers of French Guiana form two groups geographically situated on either side of the Kourou River; (2) two alleles can serve as geographic markers,Ldh2(l30) showing an affinity between the populations in eastern French Guiana and Brazil, andMe 1(300) being specific to the west.These observations are probably related to the refuges that were formed in the Quaternary in South America, especially on the Guiana Shield. We consider that the populations of French Guiana are separated into two groups at the boundary between the two migratory flows, one arising in the west from the refuge of the Guiana Shield and the other in the east from a nearby undetermined Amazonian refuge.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03522.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb03523.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY