A lot of weapons are but militarized tools, it is true also for combat around water. The fishing weapons are not limited to water environnement, but their design incorporate things learned fishing or boating.

We'll talk about, the harpoon and barbed range weapons, the trident and the net.

Harpoon and barbed weapons

The harpoon is a throwing spear, it is larger than a javelin but not as big as a spear, it can be use as a spear, but is really meant to be thrown. They are heavier and sturdier than javelins because they are intended to hot targets under water, they are barbed because they are intended to lodge into the target and they are often attached to ropes to make for easier recovery of the weapon and prey.

barbed weapons once lodged, need extra care to be removed or they'll deal damage again when teared out of the target, note that barbed weapon contrary to serrated ones do not deal "nastier" wounds, it is once lodged that they reveal their extra damage power, and barbed weapons are also more expensive to produce and harder to craft.

Depending on the size of the harpoon, closer to a javelin, it was use with an atatl, to extend throwing range and strength.

picture from Tim Rast found here

Trident

The trident is the next step in harpoon design, closer to the spear, the trident is not meant to be thrown, but can be. it is a spear with a three barbed teeth head. As the harpoon it is intended to lodge into the target in order to be able to drag it to the attacker, as a barbed weapon, removing the lodged teeth will tear flesh and increase damages. the forked design also make the trident a good disarming weapon.

The net

The weapon of the retiarii gladiator, the weaponized net is not made of rope like the fishing ones, it is made of leather with lead weights and sometimes slightly barbed. it is intended to be thrown but the range is short no max than 4 or 5 m. The objective is to entangle the target, limiting both its movement and actions. The net once thrown can be picked up and thrown again, but with less efficiency, it has to be properly folded in order to deploy correctly, but even so it still is a good weapon to trip the enemy legs, arms or head.

Elyrian transposition

Without surprise the both tribes that live in an "aquatic" biome are the ones going to use such type of weapons, To'resk and Dras, will need to be able to hunt prey, living or fleeing under water and will need to retive them. The skills and craftmanship polished using those tools will naturally transfer to their weapon counterparts.

Both tribes will have elaborate barbed designs for their arrow and spear heads. I see the net being more a To'req weapon, partly because of the To'resq aquatic farming techniques that will probably require capture of live fish. it is also possible that the To'resq develop balista size harpoon, for both ship warfare and whale hunting.