Sander lucioperca hasbeen introduced in Morocco since 1939. This noble fish has shown a good ability to acclimatize to Moroccan conditions and has developed well [1]. The present study examines diet composition and predator-prey relationships that are dependent on size and weight between sander and its preys during the period October 2018-April 2019. Stomach contents of 287 specimens, whose size varies between 17 and 72 cm, from Al-Massira dam, wereanalyzed. The results showed that Sander feeding is composed of six categories of prey, the most important species was the Blue gill (Perch) with an occurrence index equal to 14.9%, the occurrence indices for other preys were respectively : Pike perch (8.01%), Tilapia (5.57%), Roach (0.69%), Black bass (0.69%) and Common carp (0.69%). It has been found that the total length of the preys increases with that of the Pike perch. Thus, the Pike perch is able to ingest preys of big weight and size. We also revealed that cannibalism was high, indicating a lack of forage fish in this lake.

The current study describes the length-weight relationships and relative condition factors (Kr) of three species during the period (September 2020January 2021). For this purpose, 137 fish were sampled. The “size-weight”relationships thus established for each species are: Largemouth Bass: Tw = 0.0055Tl3.2816, Cyprinus carpio: Tw = 0.0148 Tl2.9417 and Oreochromis niloticus: Tw = 0.0304 Tl2.8386. These results showed positive allometry for the first species (Micropterus salmoides) and a negative one for the two other species. The relative condition factor (Kr) is higher than one, which shows that these species are in good conditions at the Al-Massira dam.

The growth parameters of three species were studied for the first time in the AlMassira Dam. A total of 137 individuals were examined during this study between September 2020 and January 2021. The estimation of growth parameters was carried out by size structure analysis using FISAT II software. The growth parameters of Micropterus salmoides, Cyprinus carpio and Oreochromis niloticus are respectively: L∞= 35.11 cm, K= 0.58 year-1, t0= 0.57 year; L∞= 44.85 cm, K= 2.60 year-1, t0= 1.27 year and L∞= 45.26 cm, K= 0.32 year-1, t0= 0.33 year. Thus, the Von Bertalanffy growth equations are written respectively: L(t) = 35.11 (1-e-0.58 (t+0.57)), L (t)= 44.85 (1-e-2.60 (t+1.27)) and L (t)= 45.26 (1-e-0.32 (t+0.33)).

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The mortality parameters and exploitation of Sander lucioperca were studied for the first time in the reservoir of Al-Massira Dam. These parameters were estimated based on sizefrequency data processed by FISAT II software. Parameters such as total mortality (Z), natural mortality (M), fishing mortality (F), and exploitation rate (E) obtained are respectively 1.71 year-1; 0.42 year-1; 1.29 year-1 and 0.75. This study thus shows that this species undergoes fishing mortality (1.29 year-1) much higher than natural mortality (M = 0.42 year-1). Furthermore, Sander lucioperca is found in a state of overexploitation with an exploitation rate (E = 0.75) higher than the estimated maximum exploitation rate (Emax = 0.65).