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The inland water fishes of Africa

 | 
Didier Paugy
, 
Christian Levêque
, 
Olga Otero

Reproduction

Didier Paugy, Christian Levêque et Fabrice Duponchelle

Résumé

The reproductive cycle of a species implies a set of physiological and behavioural processes influenced by various factors in the abiotic and biotic environment. Traditionally a distinction is made between gametogenesis and spawning. Gametogenesis is the physiological process involved in gonad development that leads to the formation of gametes (oocytes and spermatozoa). In tropical regions, gametogenesis is controlled by tiny changes in environmental factors, and its duration varies according to species (Munro, 1990). Spawning is the critical moment of the reproductive cycle, which includes the sequence of events that leads to laying of the gametes (maturation of oocytes, ovulation, spermiogenesis), under the influence of specific stimuli (Billard & Breton, 1978).
Gametogenesis is the longest of these processes. It generally lasts several months, but reproductive success depends to a large extent on the success of a set of behavioural activities. These include the search for partners, parental care before and after spawning, whether or not migration is required to find suitable sites for eggs and larvae, synchronization of spawning with changes in environmental factors, synchronization of the genital products laying, etc. These activities may be accompanied by a set of phenological adaptations, such as the development of secondary sexual characters with regard to morphology or colouring.
The study of the fish reproductive cycle thus requires a multidisciplinary approach that involves ecologists, physiologists, ethologists, and geneticists. Coordinating all these disciplines is not always a straightforward affair, and explains why data is often fragmentary. Yet we need studies that include them if we want to understand the cause-and-effect relationships between environmental factors, physiological processes, and reproductive behaviour of species.

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Extrait du texte

Gonad maturation and fecundity

Reproductive effort is the fraction of absorbed energy that an organism devotes to its reproductive activities. This investment can be partially measured through the amount of material or energy stored in the gonads, keeping in mind that it would also need to add all the energy spent on eggs or larvae care, or on mating displays.

Gonado-somatic index

To describe the growth of gonads in relation to body mass, scientists frequently use the gonado-somatic index (GSI) which is the ratio of gonad weight to body weight excluding gonads:

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where GW is the weight of the gonads and TW the total weight.

The growth of ovaries during the gonad maturation cycle reflects the growth of oocytes through yolk accumulation. The GSI of mature females varies widely from one species to another. It can reach 20 to 30% prior to spawning in some species, but only remain at a few% in others (tables 10.I and 10.II).

In many tropical species, testes develop much less than ovaries, and fo...

Auteurs

Research director at IRD. He has published numerous works on the systematics, distribution, and ecology of West African fresh water fishes, and expanded the collections of the MNHN in Paris.

Research director at IRD. He has published numerous works on the systematics, distribution, and ecology of West African fresh water fishes, and expanded the collections of the MNHN in Paris.

© IRD Éditions, 2017

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