Teratology and Early Fish Development

SYNOPSIS. The developing teleost embryo is a highly complexand balanced physico-chemical system in equilibrium with itsenvironment. Even slight alterations of the external aquaticenvironment, or a pathochemical modification of the immediatematernal environment, may lead to developmental modifications.Multiple malformations produced as a result of metabolism ofteratogens and interacting factors are similar to syndromesobtained by hybridization. Modifying factors, although possessingsome specificity as to intracellular targets are nonspecificas to the types of anomalies produced in most instances. Embryonic responses to teratogens occur at various developmentalstages and at different levels of organization, modifying thenormal development. Intracellular molecular syntheses and sensitivemetabolic targets essential for normal development may be blockedor modified, and rates of differentiation and growth affected.Embryo-sensitivity and resistance is related to tolerance leveland regulatory capacity. The terata observed have been correlatedwith molecular mechanisms and disorganization with disruptionsof cellular contacts and translocatory yolk cytoplasmic movements. Causality as it pertains to early teleost aberrant developmentis reviewed, and suggestions for research and an extensive bibliographyof the relevant literature provided.     

Teratology on the crossroads: historical aspects and modern approaches

Teratology is the science of congenital developmental disorders (CDDs), overt or latent defects of the organism resulting from the effect of internal and external factors on developmental processes. In this article the significance and position of present-day teratology is discussed in the context of development of this branch of science and related disciplines. The authors present an updated overview of the most important milestones and stages of the development of teratology. Based on the analysis of the historical development of theses and theories that represent a decisive contribution to this field, we present a survey of the fundamental principles of experimental and clinical teratology. The aim of observing these principles is to get insight into developmental relations and to understand mechanisms of action on the level of cell populations (elementary morphogenetic processes), tissues and organs. It is important to realize that any negative intervention into the normal course of these processes, either on genetic or non-genetic basis, inevitably leads to a sequence of subsequent changes resulting in the development of congenital developmental disorders. Despite modern approaches of molecular biology and genetics, along with top diagnostic techniques, we are still not able to identify the actual cause in more than 50% of all congenital defects. One-half of the unidentified cases are referred to as "multifactorial", a term that is rather ambiguous. It either means that some of the basic principles of teratogenesis still escape our attention, or the interpretation of some of the well known principles might be misleading. A third possibility is rather pessimistic. The development of the individual is so sophisticated and dependent on a delicate network of a multitude of factors mutually affecting each other that it is extremely prone to give rise to a plethora of spontaneous errors which are unpredictable and impossible to prevent. Nevertheless, the long and complicated history of scientific endeavour has yielded considerable present-day knowledge on causes and mechanisms of CDDs, a history whose beginnings date back to antiquity.     

Teratology and pathology of some Paleozoic conulariids

Conulariids exhibiting various pathologies and teratological conditions have been examined from Paleozoic rocks of North America, South America, Europe, and Africa. Published examples of teratological conditions in conulariids have been reviewed. To these cases we add a specimen of Paraconularia missouriensis (Swallow) from the Mississippian of Ohio which possesses six faces. The supposed three-sided conulariid species Conularina triangulata (Raymond) is based upon a specimen which is not a conulariid. This genus is removed from the phylum Conulariida and is considered incertae sedis. Pathologies include injuries to the exoskeleton which are grouped into patterns termed scalloped, cleft, and embayed. Scalloped injuries represent minor chipping at the aperture of the conulariid exoskeleton, and may have occurred accidentally or through predation. Cleft and embayed injuries, found only on post-Silurian taxa, indicate that conulariids suffered severe sublethal attacks more frequently after the rise of several types of durophagous predators in the middle Paleozoic. Some middle and late Paleozoic conulariid species strengthened the exoskeleton, perhaps to resist predation. Regeneration of injured integument or rods has occurred in conulariids exhibiting damaged exoskeletons.