Commercial fishing is reserved to citizens only. There no restrictions on foreign investment in aquaculture activities.
"2. In these Regulations unless the context otherwise requires - [...]
"commercial fishing" means the catching of fish by the use of factory-made gill nets or any gill net made out of factory-made materials such as leads, twines, corks, etc; 
[...]
Application for commercial fishing licence
6. (1) An applicationfor a commercial fishing licence shall be made in Form A set out in Schedule 1.
(2) An authorised officer may issue a commercial fishing licence to anyone who-
(a) is a citizen of Botswana; [...]" (Fish Protection Regulations, 2016 (S.I. No. 16 of 2016))

Fish Protection Regulations, 2016 (S.I. No. 16 of 2016)
[<a href="http://faolex.fao.org/docs/pdf/bot174293.pdf">Regulation</a>]