摘要:

A comparison of spawning features, eggs and larvae between spined loach from northern Italy and northern Germany revealed differences in egg size, clutch size and number of portions per female. Larvae differed in the presence of a ventral pigment row inC. taeniawhich was absent inC. bilineata.Two pigmentation intensity morphs occurred inC. bilineatalarvae while inC. taenialarvae only one morph was observed. These differences (and the observations of others) suggest that the two taxa are different species.

ISSN:1125-0003    

DOI:10.1080/11250009809386817

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Alburnus albidusis an endangered and little known cyprinid fish species endemic in southern Italy. Histological characteristics of testes ofA. albidusfrom River Alento, Campania Region, were analysed every month between January‐July 1996. Depending on the relative abundance of spermatogonia, spermatocytes, sper‐matides and spermatozoa in the testes, we devided the gonadal cycle into four stages: 1. quiescence, when mainly spermatogonia were present (January‐February); 2. recrudescence, when spermatocytes were abundant, although spermatids were also detectable (March‐April); 3. spawning, when cysts contained all stages of germ cells (May‐June); 4. Postspawning, when testes contained spermatogonia only (July). The concentration of sex steroids (an‐drogens, 17 α‐hydroxyprogesterone and 17 β‐estradiol) fluctuated throughout the year. Androgen levels were high during the quiescence and the spawning periods. 17 α‐hydroxyprogesterone concentration showed a sharp increase just before the spawning period. 17 β‐estradiol levels were quite low, with the exception of a slight increase during the recrudescence and the spawning periods.

ISSN:1125-0003    

DOI:10.1080/11250009809386818

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Evidence of sexual maturation and the increasing number of grass carp (Ctenopharyngodon idella), silver carp(Hypophthalmichthys molitrix)and bighead carp(Hypophthalmicthys nobilis)populations, indicate their establishment in the River Danube (Yugoslavia). It will be necessary, to undertake regulation of their abundance to insure survival of native riverine fishes in the area.

ISSN:1125-0003    

DOI:10.1080/11250009809386819

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Varicorhinus capoetais a cyprinid species widespread in Middle Asia. In Armenia about three subspecies are recognized and one,V. c. sevangiis endemic of Lake Sevan. The habits of this taxon in the lake are analysed and compared with these of others subspecies known from Middle Asia. Females in lake Sevan reach sexual maturity at age 7+ while in others basins maturity is reached at about age 3+ or 4+. Males in this lake reach sexual maturity at ages 3+ (one year later than other subspecies). Geographic isolation and characteristic features of the ecosystem of Lake Sevan (i.e., high altitude and low temperatures) probably affected the evolution of biological features and morphological differentiation ofV. c. sevangifrom other representatives of the genusVaricorbinusin Armenia.

ISSN:1125-0003    

DOI:10.1080/11250009809386820

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

About 10000 huchen larvae, obtained by artificial spawning, were introduced on 28 May 1995 into the River Tresnjica, a tributary to the River Drina, using procedures applied routinely by local fishing associations. During next two months, only 33 fry were caught in the river. Nevertheless, valuable information has been obtained for the first time on young huchens in the Drina basin. The fry apparently selected slower or almost stagnant water habitats outside the main river course. The variability of prey organisms found in fry stomachs decreased with fry length. Larger and particularly motile prey, especially mayfly larvae, gradually dominated the fry diet. Also for the first time, we document homing instinct in huchens with mark‐recapture information: one out of the nine adults, tagged after spawning, was recaptured the following year at the same spawning site.

ISSN:1125-0003    

DOI:10.1080/11250009809386821

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Feeding development of aspAspius aspiuslarvae was studied during rearing in Lake Maroz (north Poland) illuminated cages. The initial rearing occurred under controlled conditions in a hatchery. After four and half weeks, reared fish (total length 14.8 mm) were transported to cages maintained in a lake. The initial stocking density was about 8 830 fish per cage. All experiments were replicated three times. Fish were fed Zooplankton collected during night with a light placed over the cages. During the seven weeks rearing period in lake cages survival was relatively high (over 72%). The observed feeding development pattern was as follow: rotifers,nauplii, copepodites, adult Copepoda, then adult Cladocera. The largest asp larvae also ate imago forms of insects.

ISSN:1125-0003    

DOI:10.1080/11250009809386822

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Little is known about age and growth ofBarbus meridionalisin Europe and no published data are available for Slovenia. Age determination (scales) and growth studies were conducted on 561 specimens from the River Sora (west prealpine subregion) and 534 specimens from the River Gračnica (east prealpine subregion). The age structure of the species is similar in both rivers with fish from age group 0 (under yearling) to age group 6 (six years old). The number of the youngest caught specimens (0–1) was 183 from the Gračnica River and 404 from the Sora River, whereas the number of the oldest fish (5+‐6+) was 13 and 42, respectively. When compared to known age‐and‐growth data for other European populations ofB. meridionalis, the population from the River Sora approaches the upper length limit, while the population from the River Gračnica is smaller.

ISSN:1125-0003    

DOI:10.1080/11250009809386823

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Telestes montenegrinusis a little known cyprinid species endemic in the Moraca river basin (Adiatic watershad) in western Balkans. The growth rate was performed by examinations of annual rings on scales, fish length, and retroactively according to the Monastirsky's method. Results showed that the species is subjected to three periods of intensive growth, and two periods of slower growth. The highest weight increment occurs between the first and second year of life, while in older the rate is lower. In comparison with the congeneric speciesT. soufflafrom River Dri‐na (Danube basin),T. montenegrinusshows a lower growth rate. This can be the result either of different ecological conditions of the two rivers or genetic divergences among the two taxa.

ISSN:1125-0003    

DOI:10.1080/11250009809386824

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Feeding during the development of Eurasian perch(Perca fluviatilis)larvae was studiedin situin cylindrical cages. Initially perch larvae were maintained in cages, 0.2 mm of mesh size. The initial stocking density was 7 000 larvae per cage. Fish were fed with Zooplankton and after 17 days were transplanted to cages with a larger mesh size (1.2 mm). Development was observed for additional 17 days. Larval survival was about 25% and 65% for the initial and secondary rearing, respectively. Perch larvae ate initially rotifers and later ate nauplii and copepodites. Cladocera was the dominant food item in the diet of perch at the conclusion of our observations.

ISSN:1125-0003    

DOI:10.1080/11250009809386825

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This study investigates the biology ofEsox luciusin an irrigation ditch, Storta Roggia (Torviscosa, Udine), in the lower plain of Friuli‐Venezia Giulia (north‐eastern Italy). About twenty fish were captured monthly from May 1996 to May 1997. Variables such as age (as determined from reading scales) and stomach contents were recorded from these fishes. Additionally, the gonads were excised and fixed to assess the reproductive stage. These fishes were from eight age‐classes (0–7 years). Age classes 6 and 7 were chiefly females. Their diet was chiefly fish and benthic macroin‐vertebrates. Their reproductive period was from the second half of March to May. Several female specimens collected within the second half of April and May were in a spent‐spawning condition or with degenerative oocytes. Some male pike from age‐class 1 attained maturity, while females did not attain sexual maturity until age‐class 2 or later.

ISSN:1125-0003    

DOI:10.1080/11250009809386826

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor