Diet and growth of the roach Rutilus rutilus (Linnaeus, 1758), an invasive species in Ghrib dam lake (Algeria)

A total of 1,387 individuals of the roach Rutilus rutilus, ranging from 10 to 30 cm TL (9 to 428 g), were sampled between April 2013 and March 2017 in Ghrib dam in Algeria where the species was accidentally introduced. The number of preys identified in fish stomachs examined is 947. The mean digestive vacuity coefficient (CV) is 56.9%, with a low value in autumn (CV = 33%) compared to spring (CV = 80%). The diet consists mainly of crustaceans (Cladocera, Copepoda) with a main food index (MFI) of 70. Females live up to 5 years and males to 4 years. Their linear growth is described respectively by the following models of Von Bertalanffy: LT = 32.2 (1 - e0.36(t + 0.07)) and LT = 28.2 (1 - e0.41(t + 0.04)). Females grow larger than males, both having a majorant allometric coefficient of the length-weight relationship (3.36 in males, 3.42 in females). Their growth performance index is equal to 2.5 regardless of sex. This index ranks the growth of the population of the Ghrib dam among the best performing R. rutilus population.