Mare Rancidore

Mare Rancidore is a disease spreading through oily fish in the seas off of Vistilia and Styracedon.
First recorded in the 1657^th year and described in the 1663^rd year. The silvery scales of afflicted fish appear "tarnished" or "rusted" in character, without their lustrous sheen. The oils that the fish are prized for turn rancid and unsuitable for use. When used as a cooking oil it creates a "foamy" and acidic tar, and as a lamp oil it burns with a foul odor akin to "a thousand rotten onions". The flesh, barely tolerable for eating already, is said to become utterly vile. The infliction is observed to significantly increase mortality in afflicted specimens returned for study, and appears to prevent spawning, leading to shrinking populations which are less able to recover their numbers. It has been suggested that the affliction is linked to the volcanic ash clouds drifting over the sea from Styracedon, however this has not yet been either proven or disproven.
This infliction is universally detested by fisherman up and down the coasts of Vistilia and parts of southern Tremany. Ruining their hauls, the rancid character of the oils makes the fish economically worthless with no known use for the afflicted fish. Even fertilizer made from fish bone is considered to be sub-par. Its continued spread among oily fish populations has contributed to economic hardships among the fishing communities that rely on them, especially in southern Tremany where the long voyage to the schooling fields and the limited size of their hauls make the effects more keenly felt.
The drop in supply of high quality fish oils for lighting and for cooking has drastically raised the market price, forcing many lower income households to seek cheaper but potentially lower quality alternatives. The increased demand for olive oil as an alternative has increased prices and created shortages of that too. This has directly led to an economic boon for the handful of land owners responsible for the olive plantations, and has created several wealthy Ducci in charge of the shady syndicates in charge of producing and distributing the oil.