Feeding ecology of the exotic red swamp crayfish, Procambarus clarkii (Girard, 1852) in the Guadiana River (Swiberian Peninsula)

The feeding ecology of the red swamp crayfish, Procambarus clarkii was studied from October 1999 to September 2000 in the River Guadiana, the fourth largest river in the Iberian Peninsula. Analysis of the gut contents of 1225 individuals [15.8-172.3 mm total length (TL)] from 23 sites showed a diet dominated by plants [Relative Importance Index (RI) 50.34] and animals (RI 31.25), followed by amorphous material (RI = 12.21) and sand (RI 6.20). Animal food items were represented by insects, mainly dipterans (RI = 34.59) and ephemeropterans (RI = 16. 10), crayfish (RI = 15.14), and fish (RI = 11.40). Classes I (TL <= 40 mm) and 11 (TL = 40.1-80 mm) had a diet dominated by animals and amorphous material. Classes III (TL = 80.1-120 mm) and IV (TL > 120 mm) had a diet dominated by plants and amorphous material. Plants were consumed by all classes throughout the year, being most important for classes III and IV in autumn and winter. For classes I and II, animal diets are important throughout the year with increasing consumption in autumn and winter. Crayfish fragments were found throughout the year in all classes with more importance in spring and summer for classes III and IV. Similarly, fish were found in the guts of the crayfish throughout the year, this prey being more important in classes III and IV in the cold seasons. The diets of males and females were very similar, although females consumed more plants (RI = 48.72) than males (RI = 46.58). In contrast, males consumed more animal prey than females (RI = 32.36 and RI = 31.30, respectively). Differences in diet between males and females were not significant (G = 0.189, df: 3, P = 0.973).