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An insight is made into the main processes that occur in fish during endogenous feeding period. The ways in which yolk absorption rate can be measured are evaluated. Essential amino acids and polyunsaturated fatty acids are preferentially retained for incorporation into body tissue. Profound physiological and anatomical changes in yolk and a sequence of slow, fast, and a second period of slow absorption occur during the endogenous feeding period. Attempts to quantify the ontogenetic sequence are reviewed. Various methods of body size assessment are compared, and sources of bias in individual and population growth estimates are discussed. Several calorimetric methods are compared of which direct calorimetry using an oxygen bomb is the reference method. An advanced elemental analysis (CHNS) is a reliable technique that is adequate for early stages. Indices of growth potential are reviewed including a comparison of different measures, models and approaches used to estimate growth. Changes in body hydration, caloric value, content of lipids, protein, free amino acids (FAA) and minerals, and in content of RNA and DNA occur in early ontogeny. Ways to quantify metabolic rate are identified. Mean relative respiration rate of initial egg before activation is very low, about 20 mm 3 g À1 h À1 . Ontogenetic sequence in absolute metabolic rate of fish embryos and yolk-feeding larvae involves an increase through hatching to a peak at the time of first feeding ability, and a decrease under starvation. Models predicting the relationship between oxygen consumption and age in yolk-feeding fish are reviewed. Sequence of metabolic fuels begins with use of small molecules as carbohydrates, soon switched to FAA. Later lipids are progressively used, they provide energy for swimming activity. After yolk depletion body protein-bound amino acids are mobilised. In this review I focused on the major environmental variables as temperature, oxygen, salinity, pH, toxic xenobiotics, light, UV radiation, magnetic field and substrate, along with intrinsic factors as egg or body size, sex and genetic factors. A question was posed on how the extrinsic and intrinsic factors determine yolk absorption, growth and metabolic rates in yolk-feeding fish. Special attention is devoted to fish body size attained exclusively on yolk. A considerable variety of body size responses to temperature was found, for which several explanations are forwarded. Methodological progress made recently is characterised and the most conspicious advances in understanding of fish early life history are highlighted. Information derived from these studies can be used in management of fish populations in the field and to optimise activities in aquaculture.

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Fertilized Chondrostoma nasus eggs were incubated at 10, 13, 16 and 19 C until full resorption of the yolk sac. High survival was observed at 10-16 C (89-92% at the onset of external feeding), whereas at 19 C survival was depressed (76%). The time at which 5, 50 and 95% of individuals had hatched, filled the swim bladder, ingested the first food and fully resorbed the yolk sac was determined. An increase in temperature accelerated development and made it more synchronous. Within the period from fertilization to hatching embryonic development was theoretically arrested (t 0 dev ) at 8·8 C, and growth was arrested (t 0 gr ) at 8·86 C. For the whole endogenous feeding period (from fertilization to full yolk resorption) the amount of matter transformed into tissue was temperature independent between 10 and 19 C. Respiration increased exponentially with age; the respiration increase was faster at higher temperatures, but, in general, metabolic expenditures of C. nasus were low. As a consequence, the efficiency of utilizing yolk energy for growth was high as compared with other fish species (57% during the whole endogenous feeding period); it was temperature independent. However, time was used less efficiently at low temperatures, increasing a risk of predation. Within the endogenous feeding period a shift from lower to higher temperatures for optimal yolk utilization efficiency was observed. The temperatures optimal for survival and energetic performance seem to be 13-16 C for egg incubation and 15-18 C for rearing of yolk-feeding larvae. Chondrostoma nasus is a potential candidate for aquaculture for restocking purposes. 1998 The Fisheries Society of the British Isles

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Based on an extensive literature search (1,000 references), the objectives of the present study were to establish a numerical clustering of temperate freshwater fish based on their reproductive traits and to evaluate whether it was possible to extrapolate zootechnical knowledge among species belonging to the same cluster. About 65 species were classified into ten homogeneous clusters from the analysis of 29 reproductive traits, among which the most important were temperature during spawning, egg incubation and larval rearing, degree-days for incubation, larval size upon hatching, spawning season, and parental care. From this typology, a rather regular continuum of reproductive clusters emerges with two obvious endpoints. Between these two extremes, species could be ordered chiefly according to temperature requirement, spawning season and parental care. In conclusion, this new typology, differing significantly from all others proposed earlier, may now serve as a possible framework to help enhancing the domestication of new species by comparison to species belonging to the same cluster.

Based on the analysis of six egg variables and incubation temperature of 65 temperate freshwater fish species, the possible relationships between oocyte diameter, incubation time and incubation temperature were reassessed and compared to the results obtained from marine fishes. Most freshwater species have eggs (mean +/-s.d. 2.19 +/- 1.52 mm) larger than marine species, that are chiefly demersal and develop stuck to various substrata, such as plants or rocks. A strong negative relationship was found between incubation time (t, days) and incubation temperature (T, degrees C): t = 186.23e(-0.197T) (r(2)= 0.87). A strong dependence of incubation time on oocyte diameter (Ø, mm) and incubation temperature was also found and was defined as: log(10)t= 3.002 + 0.599 log(10)Ø - 1.91 log(10) (T + 2), which explained 92% of the variance of the data set. Five major groups of species were defined based on the principal component analysis (PCA) of four quantitative variables. There were two distinct groups of salmonids, displaying demersal and non-adhesive eggs with a long incubation time at low temperature, the eggs of which required a high number of degree-days. There was a large group of species possessing small, mostly demersal and adhesive eggs developing at high temperature during a short period of time, and requiring a low number of degree-days. Between these two extremes, there was a fourth group displaying intermediate values and a fifth group including three species with large, adhesive and demersal eggs incubating at high temperatures during a short period of time. The burbot Lota lota displayed an unusual combination of variables compared to the remaining species in the data set.