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Titre du document / Document title

The breeding season of tilapia, Oreochromis niloticus L. in Lake Awassa (Ethiopian rift valley)

Auteur(s) / Author(s)

ADMASSU D. (1) ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

(1) Department of Biology, Addis Ababa University, P.O. Box 1176, Addis Ababa, ETHIOPIE

Résumé / Abstract

The breeding season of Oreochromis niloticus in Lake Awassa was studied from fish caught monthly from December 1987 to November 1988 in relation to a number of environmental factors. Fish at various stages of gonad development and spawning were caught in almost all months, but breeding fish were more frequent twice a year : main peak occurred during January-March and a secondary one occurred during July-September. Gonadosomatic index (GSI) values peaked twice in the study year, a major peak being during January-March and a less pronounced one during July-September. Thus, it was concluded that O. niloticus in Lake Awassa breeds intensively in the former and less intensively during the latter period, and that some breeding occurs at any time of the year. Intensive breeding activity during January-March appeared associated with increase in solar radiation and sunshine hours d-1 whereas that during July-September appeared associated with heavy rainfall. However, intensive breeding in both periods coincided with increase in phytoplankton biomass. Previously, phytoplankton biomass in this lake is shown to increase following increase in nutrients due to mixing- and rainfall-associated changes in the hydrography and hydrology of the lake. Thus, although further studies are required, increase in phytoplankton may be one of the environmental cues to stimulate spawning in O. niloticus in Lake Awassa whereas other factors such as sunshine and rainfall may have indirect roles through their effects on the hydrology and hydrography of the lake ultimately resulting in changes in phytoplankton biomass.

Revue / Journal Title

Hydrobiologia    ISSN  0018-8158   CODEN HYDRB8 

Source / Source

1996, vol. 337, no1-3, pp. 77-83 (26 ref.)

Langue / Language

Anglais

Editeur / Publisher

Springer, Dordrecht, PAYS-BAS  (1948) (Revue)

Mots-clés anglais / English Keywords

Breeding season

;

Development

;

Gonad

;

Seasonal variation

;

Population density

;

Biomass

;

Phytoplankton

;

Lakes

;

Ethiopia

;

Oreochromis niloticus

;

Cichlidae

;

Freshwater environment

;

Environmental factor

;

Africa

;

Pisces

;

Vertebrata

;

Mots-clés français / French Keywords

Saison reproduction

;

Développement

;

Gonade

;

Variation saisonnière

;

Densité population

;

Biomasse

;

Phytoplancton

;

Lac

;

Ethiopie

;

Oreochromis niloticus

;

Cichlidae

;

Rift Ethiopien

;

Milieu eau douce

;

Facteur milieu

;

Afrique

;

Pisces

;

Vertebrata

;

Mots-clés espagnols / Spanish Keywords

Temporada reproducción

;

Desarrollo

;

Gónada

;

Variación estacional

;

Densidad población

;

Biomasa

;

Fitoplancton

;

Lago

;

Etiopia

;

Oreochromis niloticus

;

Cichlidae

;

Medio agua dulce

;

Factor medio

;

Africa

;

Pisces

;

Vertebrata

;

Localisation / Location

INIST-CNRS, Cote INIST : 5329, 35400006120498.0070

Nº notice refdoc (ud4) : 2522705



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