摘要:

Oocytes and eggs from teleost fishes are always surrounded by an egg envelope of variable dimensions. This envelope (zona radiata) in teleosts normally consists of two layers, a zona radiata interna and a zona radiata externa. The chemical composition of the interna is proteinaceous. Neutral and acid mucopolysaccha‐rides are the main components of the externa. The zona radiata interna is largely responsible for a protective function, whereas the zona radiata externa is used to attach the eggs to the substrate where they are deposited. For the latter it is equipped with variable mechanisms such as special sticky layers (e.g., inPhoxinus pboxinus, Chalcalburnus chalcoides mento, Esoxsp.,Lota lotaand 1‐eggs in cichlids), hexagonal patterns (e.g., in many percids and in channichthyids), villi‐like protuberances (= attaching‐plugs; in many cyprinids), attaching‐filaments (e.g., in gobies and blennies, p‐eggs in cichlids, piranhas and clariids), a jelly layer(Perca fluviatilis)or a muco‐follicle epithelium(Silunis glanis).This enables not only an attachment to the substrate but the eggs also can be placed in clusters and may be protected by the fish species which guard their egg deposits. In water bodies which have little or greatly reduced available oxygen, the eggs may be attached to plant tips and thus help to ensure adequate supplies of oxygen.

ISSN:1125-0003    

DOI:10.1080/11250009809386857

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Pomacentrids display a significant biodiversity through a variety of sympatric species with various feeding habits. The use of ecomorphological methods, based on the study of skeletal and muscular structures of the feeding apparatus could result in a better understanding of the adaptive radiation of this family. Significant differences in teeth and in the shape and thickened areas of the different bones were observed. The strongest structures occur in species which had teeth characteristic of suction feeding, and the weakest structures in species with biting teeth.

ISSN:1125-0003    

DOI:10.1080/11250009809386858

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The low surface area ofLatimeriagills has been confirmed for a range of body sizes from 450 gr to 80 kg. This is an indication of an inactive mode of life as has now been observed from submersibles. The gill septa indicate thatLatimeriaand lungfishes share an autapomorphy, presumably secondarily lost in tetrapods, since it is generally accepted that lungfishes and tetrapods are sister groups. The presence of a central venous sinus, arterio‐venous anastomoses and other features of the secondary circulation suggest coelacanths are similar to other fish groups in which such structures are present (i.e., Actinopterygii, Chondrichthyes). The absence of a secondary circulation and existence of a type of lymphatic system suggests that Dipnoi are more closely related to tetrapods than are coelacanths.

ISSN:1125-0003    

DOI:10.1080/11250009809386859

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Examination of the gill vasculature ofUrolophus jamaicensisconfirms structural differences in urolophid gill vasculature compared with other elasmobranchs. Differences include: 1) absence of a septalcorpus cavernosum;2) presence of a vessel conneaing the afferent filament arteries near the tip of each filament; 3) a vessel, possibly an extension of the afferent filament artery, that runs along the top of the filamentcorpus cavernosumwhich may connect the afferent and efferent filament arteries at the tip of some filaments. Additionally, a constriction indicating the presence of a sphincter muscle was noted on the efferent lamellar ar‐teriole inU. jamaicensis.This structure has not been previously noted in urolophids. The vascular structures in AtlanticU. jamaicensisare similar to those previously described in PacificU. paucimaculatusandU. mucosus.

ISSN:1125-0003    

DOI:10.1080/11250009809386860

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A morphometric comparison was made betweenSparus aurata (n= 88),Pagrus pagrus(n = 38) and their hybridS. aurata(female) x P. pagrus (male) (n = 81) using 15 morphometric characteristics. The morphometric characteristics of the hybrids were generally intermediate to those of the parental species. However, characteristics related to the body shape (6) were more similar to 5.aurataand those characters related to the head shape (9) were more similar toP. pagrus.

ISSN:1125-0003    

DOI:10.1080/11250009809386861

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The choice of spawning sites, winter habitat and longitudinal distribution of white breamAbramis bjoerknawas studied in an epipotamal river. Spawning was observed exclusively in riffles habitats. Adults (in winter) and age 0+ fish (throughout the year) were found only in backwaters and at low abundance. Adults were distributed in a longitudinal cline resulting from the occurrence of only three suitable backwaters for over‐wintering in the downstream part of the river. The abundance of 0+ age fish and the age structure of the adult stock suggest that white bream only recruit irregularly in the River Sieg.

ISSN:1125-0003    

DOI:10.1080/11250009809386862

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Fluctuating asymmetry (FA), the random deviation from perfect bilateral symmetry, is the basis of an acknowledged method to analyse developmental stability in animals and plants. This study investigates the fluctuating asymmetry in perch(Perca fluviatilisL.) from one natural lake (Trasimeno) and two regulated lakes (Corbara, Piediluco) of central Italy. Seven morphometric (pectoral and ventral fins length, pre‐pectoral fin distance, pre‐ventral fin distance, pectoral‐ventral fins distance, postorbital distance, head length) and six meristic (lateral line scales, pectoral and ventral fins rays, mandibular pores, upper and lower gill rakers) bilateral characters were selected to detect fluctuating asymmetry. Total and standard length, weight, sex and age were employed to investigate growth of perch. On the basis of FA levels a comparison of the three lakes was then made. Statistical analysis shows a relationship between fluctuating asymmetry levels and growth, and the possibility to order the lakes according to FA levels. Therefore, FA can be considered a tool to detect stress occurring during development.

ISSN:1125-0003    

DOI:10.1080/11250009809386863

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Histologically specific attributes of the vertebrae from fishes with four different swimming modes (i.e., anguilliform, subcarangiform, carangiform and thunniform) were studied using microradiography, natural and polarized light. Young eels (anguilliform) are structurally peculiar having 5 trabeculae in their anterior vertebae. Dorso‐central trabeculae with lateral cartilage are lacking posteriorly. Eel bone is lamellar, non‐vascular periosteal tissue and the osteocytes are arranged in rows. Other trabeculae are spongious. Anterior vertebrae in adults are also spongious. Trout (subcarangiform) have thick trabeculae peripherally. These bones are spongious and cavities are formed due to osteoclastic resorption. Secondary osteones indicate remodeling). Horse makerel (carangiform) have vertebrae that are generally spongiose, surrounded by compact bone peripherally. The vertebral cortex is parallel‐fibred, acellular bone. Vascular canals are present, apparently without orientation. Spongiosa are vascularized. Vascular primary bone are replaced by osteones. Bone remodeling gives peculiar aspect to sections. Fishes showing hyperosteosis possess compact bone rich in canals and are deprived of spongiosa. Remodeling occurred not much. Bonito showed diversity in design. Compact periphery surrounds spongious medulla. Compact bone are traversed by longitudinal and radiated canals and has osteocytes. Spongiosa has erosion bays. Remodeling confirm elevated metabolism. A distinct design for each species is clear.

ISSN:1125-0003    

DOI:10.1080/11250009809386864

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The dynamics of radionuclide accumulation by fishes in different aquatic ecosystems was studied following the Chernobyl accident. Predatory and non predatory fishes in the Chernobyl NPP cooling pond, Kiev reservoir (Ukraine), Kojanovskoye lake (Russia) and Svyatoe lake (Belarus) were studied during the period 1986–1997. Concentration of radionuclides in fishes muscles decreased significantly during the period 1986–1997. Speed of purification of fishes depends on amount of radionuclides transferred in ponds and on hydrological and hydrochemical features of the aquatic ecosystems.

ISSN:1125-0003    

DOI:10.1080/11250009809386865

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Changes of the ecosystem in the cooling reservoir of INPP have occurred since the start of the plant construction and increased when it will work at full capacity. The increase of temperatures in waters of surrounding areas caused changes and elimination of species at rates that exceed the rates found in natural water reservoirs. Examination of the fish populations indicated some adaptations among these fishes relative to the degree of plant construction and recent habitat restoration. Several species display adaptations to the altered conditions (e.g., vendace) while other species have become extinct (e.g., smelt). Some species have apparently become adapted to the altered conditions (e.g., roach, silver bream, perch and rudd).

ISSN:1125-0003    

DOI:10.1080/11250009809386866

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor