Estudios ultraestructurales de las variaciones morfológicas de la superficie y envolturas del huevo de pez-gato africano Clarias gariepinus (Burchell, 1822) antes y después de la fertilización, con una discusión de los mecanismos de fertilización

Much of the existing knowledge of the mechanisms involved in teleost fertilisation is based on a few small model species that have no commercial value. Research is therefore urgently required to address mechanisms involved in fertilisation in species of great commercial value. In this study, the ultrastructural morphological variations in the surface of the egg of Clarias gariepinus were recorded before and after fertilisation by using electron microscopy. The outer surface of the unfertilised egg was smooth, whereas the fertilised egg acquired a network of projections on the vegetal hemisphere. Moreover, different patterns of ornamentation on the egg surface were evident. This pattern of ornamentation varied with the progress of embryonic development. The micropyle of the C. gariepinus egg consisted of a funnel-shaped vestibule, from the bottom of which a cylindrical micropylar canal extended. The micropylar canal decreased in diameter after completion of fertilisation, forming a micropylar disc. The sperm behaviour on the egg surface was oriented towards any depression on the chorion surface. The chorion of ovulated eggs consisted of one layer. After fertilisation the chorion was differentiated into three layers: the double-layered coat, the zona radiata externa and the zona radiata interna. Four protein subunits of the chorion of C. gariepinus were identified by SDS-PAGE. IR-spectra obtained from C. gariepinus chorion revealed that the vibration of chorion proteins exhibited different weak activities in the IR-spectra with minor difference between pre- and post-fertilisation chorion proteins.Gran parte del conocimiento existente sobre los mecanismos de fertilización en teleósteos se basa en unas pocas especies modelo, que no tienen valor comercial. Por ello, se requiere investigación dirigida a conocer los mecanismos involucrados en la fertilización de especies de gran valor comercial. En el presente estudio, mediante el uso del Microscopio Electrónico, se obtuvieron imagines de las variaciones en la morfología ultraestructural de la superficie de los huevos de Clarias gariepinus antes y después de la fertilización. La superficie externa de los huevos infertilizados era lisa, mientras que la de los huevos fertilizados adquiría una red de proyecciones en el hemisferio vegetativo. Además, fueron evidentes diferentes patrones de ornamentación de la superficie del huevo. Este patrón de ornamentación varió a lo largo del desarrollo embrionario. El micropilo de los huevos de C. gariepinus consistió en un vestíbulo con forma de embudo desde la base del cual se extendía un canal micropilar cilíndrico. El diámetro de dicho canal disminuía tras la finalización de la fertilización, formándose el disco micropilar. El comportamiento del esperma en la superficie de los huevos se orientaba hacia cualquier depresión de la superficie del corion. El corion de los ovocitos consistió en una sola capa. Tras la fertilización, el corion se diferenció en tres capas: la capa double-acodada, la zona radiada externa and y la zona radiada interna. Mediante SDS-PAGE se identificaron cuatro subunidades de proteínas en el corion de los huevos de C. gariepinus. Los espectros IR obtenidos del corion revelaron que la vibración de las proteínas del corion exhibía diversas débiles actividades en el espectro IR con menores diferencias entre pre- y post-fertilización proteínas del corion

Erythrocytes alterations of monosex tilapia (Oreochromis niloticus, Linnaeus, 1758) produced using methyltestosterone

AbstractThe present study aims to investigate the effects of methyltestosterone on monosex farmed tilapia, Oreochromis niloticus by detection of apoptosis, micronucleus and alterations of erythrocytes. Fishes were obtained from four localities (Assiut as a control and Beheira, Alexandria and Kafr EL-Sheikh; three farms from each governorate as farmed monosex produced using methyltestosterone). Blood smears were processed for Hematoxylin and eosin technique. The major alterations recorded in the red blood cells were as swelled cells (Sc), tear drop-like cells (Tr), and sickle cells (Sk). Also, a significant difference (P⩽0.001) between three governorates and Assiut was recorded in the micronucleus test, apoptosis and altered erythrocytes. These alterations are considered as an indication for performance and health of fish in the monosex culture medium indicating the side effects of overdose induction of MT

Effects of ultraviolet A on the activity of two metabolic enzymes, DNA damage and lipid peroxidation during early developmental stages of the African catfish, Clarias gariepinus (Burchell, 1822)

Many ultraviolet-A (UVA)-induced biochemical and physiological changes are valid as biomarkers using aquatic species for detection of the degree of stress. Changes in the concentration and activities of enzymes, such as glucose-6-phosphate dehyderogenase (G6PDH), lactate dehyderogenase (LDH), DNA damage and lipid peroxidation (LPO), can be used as biomarkers to identify possible environmental contamination in fish. This study aimed to investigate the impact of UVA on the activity of the selected enzymes, DNA damage and LPO during early developmental stages of the African catfish Clarias gariepinus. Embryo hemogenates were used for measurements of G6PDH, LDH, DNA damage and LPO concentrations and activities spectrophotometrically at 37°C. The normal ontogenetic variations in enzyme activities, DNA damage and LPO of the early developmental stages (24–168 h-PFS; hours-post fertilization stage) were studied. There was a significant decrease in the activity of G6PDH till 120 h-PFS. Then after 120 h-PFS, the activity of such enzymes insignificantly increased toward higher stages. The LDH activity was recorded with a pattern of decrease till 96 h-PFS, followed by a significant increase toward 168 h-PFS. The polynomial pattern of variations in DNA damage and LPO was also evident. The patterns of the enzyme activities, corresponding DNA damage and LPO of the early ontogenetic stages under the influence of three different UVA doses (15, 30 and 60 min), were recorded. The pattern of variations in G6PDH activity in UVA-induced groups was similar to that of the control group with variation in the magnitude of such activity. In all treated groups, LDH activity decreased till 96 h-PFS, then increased till 168 h-PFS. Within each of the embryonic stages, the increase in UVA led to a significant increase in DNA damage. A significant increase in lipid peroxidation under UVA doses was recorded. The variability in number and molecular weight of proteins under exposure to UVA was evident, reflecting some of the genetic and transcriptional changes during exposure and development

Early development of the African catfish Clarias gariepinus (Burchell, 1822), focusing on the ontogeny of selected organs

Embryonic development of Clarias gariepinus was studied from oocyte activation to the end of endogenous feeding (164 h post-fertilization, 164 h-PF). The ontogeny of the eyes, the ear, the heart, the digestive tract and the notochord were described histologically: (i) eyes were not pigmented at hatching (40 h-PF) and the anlage of the retina was observed at 96 h-PF. At 164 h-PF, the pigmented epithelium was distinguished as a single layer of cubical cells and the outer nuclear layer was composed of cones; (ii) the inner ear was oval-shaped and two otoliths and a sensory epithelium were differentiated at hatching. Three semicircular canals with rudimentary cristae developed until 96 h-PF, leading to a fully developed auditory vesicle at 120 h-PF; (iii) at 40 h-PF, a beating heart appeared as a thin-walled tube and at 72 h-PF no blood elements were recorded in the two-chambered heart. The four compartments (bulbus arteriosus, ventricle, atrium, sinus venosus) and mature blood elements were found only at 144 h-PF; (iv) the hatchlings possessed an undifferentiated digestive system, and differentiation of a buccal cavity, oesophagus and intestine was only recorded 96 h-PF. The connection between the oesophagus and the intestine and the anus opened at 144 h-PF; (v) the notochord in newly hatched embryos was composed of vacuolated cells and a peripheral layer of notochordal epithelium inside a fibrous sheath. Subsequently, vacuolated cells proliferated and notochordal epithelium changed from cubical to squamous cells. Eye differentiation was concomitant with first feeding, thus suggesting a key role of visual senses in feeding behaviour