Cytogenetic analysis of three sea catfish species (Teleostei, Siluriformes, Ariidae) with the first report of Ag-NOR in this fish family

Despite their ecological and economical importance, fishes of the family Ariidae are still genetically and cytogenetically poorly studied. Among the 133 known species of ariids, only eight have been karyotyped. Cytogenetic analyses performed on Genidens barbus and Sciades herzbergii revealed that both species have 2n = 56 chromosomes and Cathorops aff. mapale has 2n = 52 chromosomes: Genidens barbus has 10 Metacentrics (M), 14 Submetacentrics (SM), 26 Subtelocentrics (ST), and 6 Acrocentrics (A), Sciades herzbergii has 14M, 20SM, 18ST and 4A, whereas Cathorops aff. mapale has 14M, 20SM, and 18ST. The nucleolus organizer regions (NORs) were found in a single chromosome pair on the short arm of a large-sized ST pair in Genidens barbus and on the short arm of a middle-size SM pair in Cathorops aff. mapale. Multiple NORs on the short arms of two large-sized ST pairs were found in Sciades herzbergii. The occurrence of diploid numbers ranging from 2n = 52 through 56 chromosomes and the presence of different karyotypic compositions, besides the number and position of NORs suggest that several numeric and structural chromosome rearrangements were fixed during the evolutionary history of this fish family

5.1 Toxicity Problems associated with Trace Elements in Domestic Animals

The opening sentence of the toxicology section of a recent veterinary pharmacology and therapeutics text reads “Everything is poisonous” (Hatch, 1977). Such a generalization reinforces the fact that this paper is concerned with the toxicity of essential trace elements which are necessary for the proper functioning of body cells and are usually thought of in their role as essential components of a diet. Thus, there is the apparent paradox of certain trace elements being both necessary for and damaging to the proper functioning of cells and of the animals that are composed of these cells. It has been said that there are not any toxic elements but that there are toxic concentrations of elements and the paradox of essentiality and toxicity is resolved if we consider that it is the concentration of the element within the biological system that determines the type of action that occurs. Very low concentrations of trace elements are required for the proper functioning of enzymes, cells and tissues. Increasing concentrations can be tolerated by cells but, at a particular concentration, the homeostatic mechanisms can no longer handle the element and cells are damaged. It has been suggested that there are three zones of action of trace elements, (i) the biological action zone, (ii) the inactive zone and (iii) the pharmacotoxicological action zone (Venchikov, 1974).</jats:p

Calcinosis Circumscripta in the Dog with Particular Reference to Lingual Lesions

Calcinosis circumscripta of the tongue is described in 6 large, young dogs. The lingual lesions are identical with calcinosis circumscripta as described in the literature and 10 subcutaneous lesions that we examined. It is suggested that the lingual and subcutaneous lesions are part of one disease process and that the former are more frequent than is indicated in the literature. Apocrine glands were not found in association with the lingual lesions or at comparable sites in the tongues of 6 unaffected dogs; it appears that their presence is not a prerequisite for the development of the lesion. Ten calcifying epitheliomas were also examined and evidence is presented which strongly suggests that this lesion be distinct from calcinosis circumscripta. </jats:p