Edited Feb 1 2019 with some additional fun stuff.
Welcome, Knight Owl!
Part of the answer may come from the ecological niche they evolved from. Otter-canines might be carnivore chasers; therefore, their military structure may be pack-based, relying on many jaws and claws to take down larger animals -- even larger predators. This psychology might stay with them into interstellar travel, so that when they attack, they attack with tightly coordinated maneuvers designed to exploit weak points in larger enemies.
That said, nothing beats energy. Kinetics are generally the best way to stop someone, so one high-tech kinetic weapon would be one where the projectile has additional propellant that ignites after being launched from a gun barrel. So imagine a slightly bulky launcher that launches at a relatively low speed, but the bullet is like a tiny rocket or missile that picks up speed.
By the way, that sort of gun also works well in zero-G combat, since its low launch velocity is less likely to cause the attacker to lose his balance due to recoil. In other words, Zero-G combat could be an equalizer for them... if Zero-G combat is a thing that is.
After that, I'd say you'd have to work in energy weapons, either plasma (which is slow but effective) or laser (which is fast and effective). Higher tech would include things like disruptors, which are slower but deadly.
Some of my assumptions are taken from my knowledge of the Traveller Role-Playing Game, of which I am a fan and contributor.
EDIT
Thanks to Adrian's excellent suggestion below, I'm now reminded of a host of exotic weaponry that Traveller5 has opened up to role-playing, including the gravitic weaponry of which Adrian speaks. Other options, which also don't have to be bulky, include:
Poisons. The dart gun can simply get high-tech. How about a geneered DNA poison tailored for the target species?
Gases. Slightly less high-tech than poisons are simply ways to introduce gases inert to the Setani but debilitating or deadly to some of its enemies.
Very High Tech Stuff. Probably beyond the Setani, unless they have access to Ancient artifacts or very high tech trade partners, would include:
Stasis guns. Causes time to stop within a small bubble. Also good for shearing off pieces of your enemy :/
Inducers. Ship guns that force a target ship into an interstellar bubble -- a misjump gun, if you will.
Gauss guns. These fire tiny flechettes at absurd speeds. Very painful.
Neural guns. Again, higher tech, but if they know how to disrupt the enemies' brainwaves temporarily, they've got the upper hand.
EMP and Flash guns. For temporary stopping.
Freeze. Why cook 'em when you can freeze 'em?
Acid. Use chemistry to disable your target. Can be painful.
Rad. Irradiate your foe. This one can be painless, or it can be cruel.
Sonics. Deafen your target. Can cause quite a bit of pain too.
Shock. A combat taser.
Relativity. Very high tech. No idea what it does, but it can't be good.
Credit where it's due. All of these come from the Traveller Role Playing Game, Fifth Edition.