I’d suggest 10 yellow labs for a 40 breeder. Correct me if I’m wrong but wouldn’t more than 6 make them less aggressive plus give a better look without having big open gaps in Between fish and like you said less breedingWith African cichlids it's honestly better to over stock then understock. An understocked tank has territories to stake claim to while in an over stocked tank there are no territories as everybody is in everybody else's space. It's actually a pretty common thing to see with African cichlid tanks as it helps to reduce aggression and the over all fry output. Granted you'll still get babies just not as frequently or in such quantity. Granted 6-7 is still not bad for only a 40g but you'll have em breeding more regularly then.