In this paper, we analyze the performance of a dual-hop radio frequency - underwater wireless optical communication (RF-UWOC) transmission systems wherein the RF and UWOC links experience Nakagami-$m$ fading and the mixture Exponential-Generalized Gamma fading, respectively. The location of $S$ is uniformly distributed in the space of the hemisphere where the relay is located in the center of the hemisphere. The effect of bubbles level, temperature gradient, water types, and detection techniques are considered. We derive closed-form expressions for outage probability (OP) and average bit error rate (ABER) for both fixed and variable gain relaying schemes with different detection techniques. Furthermore, by utilizing the expansion of Meijer's $G$-function and Fox's $H$-function, the closed-form expressions for the asymptotic OP and ABER are derived when the average signal-to-noise ratio of both links tends to infinity. The analytical results are verified by Monte Carlo simulation results. Our results demonstrate that the diversity order of the dual-hop RF-UWOC systems depends on the RF fading parameter and detection technology of the UWOC link.