Actually your plec would be more likely to harm the stingray, plecs and rays should never be kept in the same tanks as plecs seem to have a bit of a fetish for stingray slime. The rays are very sensative to any damage and if a plec removes any of their slime coating they pick up infections almost immiediatly, usually killing the ray . A arowana will probably need a larger tank in the end, silver arowana's can hit 48" when full grown and even the smaller species such as blacks and jardini's can reach 30".
What are the dimensions of your new tank? The ammount of floor space is important for how many cichlids you cant safely stock, for instance a tank that is 24" tall and 30" wide can hold more fish than a tank that is 30" tall and 24" wide, large aggressive cichlids will require between 40 and 60 gallons of water per fish!
What are the dimensions of your new tank? The ammount of floor space is important for how many cichlids you cant safely stock, for instance a tank that is 24" tall and 30" wide can hold more fish than a tank that is 30" tall and 24" wide, large aggressive cichlids will require between 40 and 60 gallons of water per fish!