Temperature is the major abiotic factor controlling the rate of morphogenesis in fish. The present work investigated hatching time and the transition from endogenous to exogenous feeding at five constant temperatures over the range 15-35 °C. Clarias gariepinus eggs can be successfully hatched in ambient water temperatures between 20 and 35 °C, although at 30 °C the hatching rate is significantly improved. At 15 °C embryos do not survive. The period of hatching is inversely related to temperature such that synchronous hatching is encouraged by high temperature within the specific temperature range. The extent to which development rate and metabolic rate in C. gariepinus are accelerated by temperature is not the same. The duration between first feeding, yolksac absorption and the point-of-no-retum is inversely related to temperature. The same threshold temperature, below which development is theoretically arrested, can be estimated for C. gariepinus from the linear relationship between development rate and temperature up to hatching, first feeding and yolksac absorption. This closely approximates the lower lethal temperature of 15 °C estimated directly from embryo survival. The effect of temperature can be usefully modelled in C. gariepinus using the linear relationship V = a + bt to estimate t0 (threshold temperature) and Deff0 (effective day-degrees) and the hyperbolic relationship τ = Deff0/(t – t0) to determine development time. From the present work, t0 is 14.5 °C and Deff0 is 13, 26.3 and 35.7 for hatching, first feeding and yolksac absorption respectively for C. gariepinus. Unlike day-degrees, effective day-degrees remain independent of temperature over the range 20-35 °C. An approximate guide to development time at different constant temperatures within this range is given.

Pike-perch Stizostedion lucioperca larvae fasted or given two diets (artificial feed, zooplankton) were studied by transmission electron microscopy and using specific cytological dyes. The objective of this work was to assess the changes in the yolk sac, liver and anterior intestine following the mouth opening stage (95 °C.d, day 5 - 5.8 mm) from endo- to exotrophy periods. The yolk sac included a syncytial envelope closely bound to the proteinaceous vitellus and the oil globule. Its development was similar to that observed in trout (Oncorhynchus mykiss and Salmo fario trutta )and sea-bream (Sparus aurata,) but without vitellus fragmentation into platelets. Vitellus resorption was never achieved in dying larvae. From the end of the endotrophic phase onwards, the amount of hepatic glycogen decreased. Carbohydrate disappeared at the beginning of the exotrophic phase then increased after 220 °C.d (day 10 - 6.0 mm), mainly in zooplankton-fed larvae. Lipids from enterocytes, sinusoids and general blood Stream showed a similar development. They were abundant at 95 °C.d, progressively disappeared up to 260 °C.d (day 12 - 6.3 mm), and increased again from 350 °C.d (day 16 - 6.7 mm) onwards if larvae were fed zooplankton. Dietary lipids did not seem to immediately replace yolk lipids despite absorption in the gut. Various hypotheses are proposed to explain the physiological abnormalities of this critical larval stage. Although zooplankton appeared to have better nutritional qualities than the artificial feed, these two foods proved to be quite unsatisfactory as they induced liver cell changes typical of food deficiency, generally observed in starving larvae.

Le développement larvaire des 4 espèces de Plécoptères Capnia ? arensi Zhiltzova, Brachyptera galeata Koponen, Protonemura libanocypria Zwick et Isoperla libanica Aubert est étudié. Ces espèces colonisent un ruisseau temporaire du Liban. C. ? arensi est une espèce hivernale, B. galeata et P. libanocypria sont printanières, I. libanica est printanière tardive.