Heleobia

Heleobia sits 1,037th of 1,059 documented fish by maximum weight: it is a snail by the wiki's description, topping out at 0.2 kg, with 0.1 kg as its minimum and 0.15 kg on average. It is a Rare fish from the Astral Observatory, listed as obtainable with Worm as bait, Night as the time, Rain as the weather and Spring as the season.

The weight is small but the price per kilogram is high, at C$1,900. That works out to an average sale value of C$285 and 260 base XP, which ranks 650th of 1,038 documented fish by average value. The wiki's quote reads "A tiny aquatic snail whose shell stores chemical compounds that lower the freezing point of surrounding water."

The Astral Observatory documents 35 fish, and four other Rare fish share the zone: Nebulous Comb Jelly, Northern Pike, Sea Angel and Hagfish.

Verdict: a light, low-value Rare that is worth logging for the Astral Observatory list, though not for profit.