This study describes the egg membrane structures of angelfish (Pterophyllum scalare), morpho-physiological changes during angelfish embryogenesis from activation to hatching under optimal conditions (28°C; pH 6.8), the developing larvae and fry, the effect of alkaline pH on the early developmental stages of the species, the relationship between food item size and fry survival. Egg membranes (thin, transparent, 1.67-2.18 µm thick) are covered by a sticky substance. The amber-coloured angelfish eggs were oval in shape, with average diameters of 1.436 and 1.171 mm, i.e., a mean volume of 1.033 ± 0.095 mm 3 . The survival rate of embryos and larvae kept in water with an elevated, slightly alkaline pH was very low: as few as 2% of the embryos survived, while in the batch kept in optimal water conditions very few eggs died. The first larvae hatched after 1288 h of embryonic development. The newly hatched larvae measured on average 2.60 ± 0.093 mm and had large (0.64 ± 0.077 mm³) yolk sacs. They attached themselves to the substrate with a secretion of thin, viscous threads, which was released from glands situated on the top of the head. The glands vanished on day 5. The 1-day-old larvae showed the first pigment cells on the body and the eyes of the 2-dayolds were already fully pigmented. Between day 4 and 5 of larval life, the larvae began feeding on live food. The 23-day-old fry looked like a miniature versions of the adults. Mortality of the angelfish larvae during their first days after hatching was higher in those fed brine shrimp (Artemia salina) nauplii than those fed protozoans and rotifers.En este trabajo se ha descrito la estructura de las túnicas ovulares del escalar o pez ángel (Pterophyllum scalare), las modificaciones morfo-fisiológicas que transcurren durante la embriogénesis del escalar desde el momento de activización para el desove en condiciones ambientales óptimas (28ºC y pH 6,8) y, se han caracterizado las larvas y los alevines desarrollándose. Adicionalmente, se ha estudiado el efecto del pH básico del agua sobre los primeros estadios de desarrollo y la dependencia entre la cantidad de alimento y la supervivencia de los alevines. Las túnicas ovulares del escalar son finas (1,67-2,18 mm), transparentes, cubiertas de una sustancia viscosa. Los huevos de color ámbar tienen forma ovalada de diámetros medios 1,436 y 1,171 mm y de un volumen medio de 1,033 ± 0,095 mm 3 . El porcentaje de supervivencia de embriones y de larvas en agua con pH aumentado, ligeramente básico, fue muy bajo, ya que sólo el 2% de los embriones sobrevivió, mientras que en agua de parámetros óptimos sólo algunos huevos palidecieron. Las larvas recién salidas del huevo medían 2,60 ± 0,093 mm por término medio y poseían grandes (0,64 ± 0,077 mm³) sacos vitelinos. Se han adherido al substrato mediante una secreción en forma de filamentos finos y viscosos. Esta secreción se ha desprendido de las glándulas ubicadas en la cumbre de la cabeza. Las glándulas desaparecieron al 5º día de vida de las larvas. Las larvas de un día poseían ya l...

Background. The stinging catfish, Heteropneustes fossilis (Bloch, 1794), has recently raised interest among fish farmers, ornamental fish keepers, and pathologists. Its natural populations are threatened due to habitat loss and high fishing pressure. A number of factors may influence the reproductive success of this. The aim of this study was to assess the effect of one of such factors-the water hardness-on the course of the embryogenesis, the structure of the egg shell, the general morphology, and the behaviour of the hatched larvae. Materials and Methods. The fertilised eggs were incubated at a constant temperature of 23 ± 0.2°C in water of different hardness: 0ºGH (soft), 9ºGH (moderately soft), 18ºGH (moderately hard). Egg membranes of activated eggs were viewed under a scanning electron microscope. Also egg membranes strength and egg deformations were determined 1.5 h after fertilisation. Images of eggs and newly hatched larvae, recorded with the observation sets described above, were measured and analysed. Results. The study showed the eggs were surrounded by thin, translucent,~5 µm thick membranes equipped with numerous outgrowths on the external surface and porous on the inner side. The following observations were made within 828 h°(degree-hour) at 23 ± 0.2°C: the highest volume of eggs (1.16 ± 0.092 mm 3 ) was typical for eggs incubated in soft water (0°GH), while the lowest egg volume (0.99 ± 0.113 mm 3 ) was recorded in eggs incubated in moderately soft water (9°GH); yolks spheres were greenish in colour, the embryonic disc and the embryo itself being reddish; the embryo performed diverse movements (quasi-peristaltic, cardiac muscle contractions); after few hours of hatching, the pigments developed resulting in colour appearance; club-like primordial barbels were formed 24 h after hatching; the larvae commenced feeding on day 3 post hatching. Conclusion. Water hardness influences embryonic and larval development and the effects may be diverse. Low water hardness is recommended for egg incubation. However, the situation changed when the egg membrane protection ceased to exist at hatching. Increasing water hardness a few hours prior to the expected hatching time prevents larval deformation.Keywords: stinging catfish, Heteropneustes fossilis, embryogenesis, eggs, embryonic motorics, embryonic morphometry, water hardnessIn addition to the species' value for fish farmers, the stinging catfish-due to some structural and physiological peculiarities-has become interesting also for the ornamental fish trade. Recently, the species has become a study object for pathologists focusing on transmittable zoonoses.The stinging catfish occurs naturally in tropical waters of south Asia, general in bodies of water abundant in vegetation, oxygen-depleted due to decomposition of the plant material, and heated by the sun throughout the water column (Munshi et al. 1976, Pandey 1978, Pethiyagoda 1991, Kahl et al. 1997, Jayaram 1999.In its native habitat, the stinging catfish attains 70 cm of total length. The sexual dimorphi...

Changes in resistance to mechanical pressure during embryogenesis were studied in the signal crayfish (Pacifastacus leniusculus Dana). A constant increase in egg size (volume and surface area) was observed to take place throughout the embryonic development, the increase occurring as most probably result of water absorption. The increase in the egg volume was found to be accompanied by a constant reduction in the egg membrane resistance.Morphomechanical aspects of crayfish hatching as well as a possibility of taking advantage of them to enhance astacid reproduction are discussed.

The egg case is an extracellular structure that surrounds an egg cell and the embryo after fertilization. Its basic function is to protect the embryo from potentially harmful aspects of the external environment. Changes in the structure of the egg case at different stages of embryogenesis in the crayfish Astacus leptodactylus were studied, with observations made at the beginning of egg incubation, during incubation, and at the time of hatching. We studied the changes using images taken with transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The egg case is made of three layers that are all close together. The outer layer was 4.59 ± 0.23 μm thick and composed of an electron-dense material; its external structure was rough. The middle layer was the thickest at 8.94±0.29 μm and was slightly folded. It was made of polyhedral grains, interspersed with multiple aeropylar areas and channels. This second (middle) layer consisted of two sublayers of equal thickness but with variable grain size and aeropyle structure. The third and innermost layer was 3.14 ± 0.33 μm thick and made of tightly packed grains, smaller than those in the middle layer. It included a few, small aeropylar channels.

The need to elucidate the hatching process in the signal crayfish, Pacifastacus leniusculus, emerged as a result of the paucity of information on hatching mechanisms, perivitelline space, and egg hydration during embryonic development.To elucidate morphomechanical changes in the eggs during embryonic development of the signal crayfish, egg diameter and egg case strength were measured. Embryogenesis itself and hatching mechanisms were observed on live eggs in a special apparatus (a microscope coupled with a digital camera, a computer, and a video-recorder). Changes in egg case structure during embryogenesis and during hatching were analysed using light and scanning electron microscopy.During the period of observation, the eggs were found to continuously increase in volume, from an initial value of 8.87 ± 0.376 to 12.25 ± 0.371 mm 3 at hatching. The egg case strength was initially considerable and exceeded 107.7 ± 11.43 g. It was, however, observed to decrease with time to 38.6 ± 15.34 g of hatching.In addition, the structure of the egg case was observed, just before hatching, to loose its integrity mainly by local absence of the inner layer. On hatching, the case would break down along the embryo's cephalothorax, where it was most conspicuously stretched. RÉSUMÉLa nécessité d'étudier le processus d'incubation chez l'écrevisse « signal », Pacifastacus leniusculus, est apparue du fait du manque d'information sur le mécanisme de l'éclosion et le processus de formation de l'espace péri vitellin et des relations hydriques au cours de développement embryonnaire.Pour élucider les changements morpho-mécaniques des oeufs de l'écrevisse signal pendant son développement embryonnaire, le diamètre des oeufs et la résistance de l'enveloppe de l'oeuf ont été mesurés. L'embryogénèse et le mécanisme de l'éclosion ont été observés sur des oeufs vivants à l'aide