The author proves for Fock spaces of \(\mathbb C^n\) necessary conditions for sampling or interpolating sequences which generalize (in a certain case) the results obtained by \textit{J. Ortega-Cerdà} and \textit{K. Seip} [J. Anal. Math. 75, 247-266 (1998; Zbl 0920.30039)]. However, for \(n>1\), those are far from being sufficient conditions, unlike in the case \(n=1\) studied in \textit{B. Berndtsson} and \textit{J. Ortega-Cerdà} [J. Reine Angew. Math. 464, 109-128 (1995; Zbl 0823.30023)]. These questions of sampling are motivated, among other things, by the study of frames of Gabor wavelets. Let \(\varphi\) be a plurisubharmonic function in \(\mathbb C^n\), define for \(1\leq p 1\). Simple examples show that conditions about those densities cannot be sufficient for either interpolation or sampling when \(n>1\). Reduction to the case \(p=2\) is relatively easy, once some technical estimates are obtained. The proof then relies, as in \textit{H. J. Landau} [Acta Math. 117, 37-52 (1967; Zbl 0154.15301)], on an estimate about the number of eigenvalues greater than some \(\gamma \in (0,1)\) of the Toeplitz concentration operator given by \(T_{\chi, \varphi}f= P_\varphi (\chi f)\), where \(P_\varphi\) is the Bergman projection from \(L_\varphi^2 := \{f: \|f\|_{2,\varphi}<\infty\}\) to \(F_\varphi^2\), and \(\chi\) is the characteristic function of a ball \(B(z;r)\). All those eigenvalues are in \([0,1]\) anyway, and it is cleverly shown by comparing the traces of \(T_{\chi, \varphi}\) and \(T_{\chi, \varphi}^2\) that they are close to either \(0\) or \(1\), which permits an estimate of the desired quantity using an estimate of the trace of \(T_{\chi, \varphi}\). This is then estimated using a trace formula involving the Bergman kernel for the space \(F_\varphi^2\), and precise estimates on this kernel which involve delicate estimates on solutions of the \(\bar \partial\) equation from \textit{B. Berndtsson} [J. Geom. Anal. 7, No. 2, 195-215 (1997; Zbl 0923.32014)].