Resource allocation in yolk-feeding fish |
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Authors: | Ewa Kamler |
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Institution: | (1) Inland Fisheries Institute, Żabieniec, Piaseczno, 05-500, Poland |
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Abstract: | 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 mm3 g−1 h−1. 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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Keywords: | Body growth Embryos Extrinsic factors Metabolism Yolk-feeding larvae Yolk absorption |
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