Oscars
A cichlid that grows to a foot and rearranges the tank to suit itself. Oscars recognise the person who feeds them and beg like a dog.
Photo by Jarek Tuszyński, CC BY 4.0
Overview
The oscar is a large South American cichlid from the western Amazon and Orinoco, and it is far bigger than most people expect. FishBase records 45.7 cm and 1.6 kg, which is a fish approaching a foot and a half and weighing three and a half pounds.
It is also slow growing, which is what makes it a trap. An oscar sold at two inches takes years to reach full size, so the tank that looked generous at the start becomes the wrong tank gradually rather than obviously.
Temperament
The closest thing an aquarium has to a pet with opinions. Oscars recognise people, beg at the glass, take food from a hand and rearrange whatever is in the tank to their own preference.
They are also predators and they are territorial. Anything that fits in the mouth is food, tank decor gets moved, and plants get uprooted. A breeding pair guards eggs on a flat surface and then guards the fry, both parents together, for roughly ten days.
Care and grooming
Small fish, crayfish, worms and insect larvae in the wild, so a quality cichlid pellet as the staple with whole frozen foods alongside. Feeder fish are a poor idea: they add disease risk without adding nutrition the pellet does not already have.
FishBase gives 22 to 25 degrees C, which is 72 to 77 F, and pH 6.0 to 8.0. A fish this size on a rich diet loads a filter heavily, so filtration is sized well above the tank and water changes are frequent rather than occasional.
Living and exercise
Seventy five gallons for a single fish, more for a pair, with heavy filtration and a lid. Decor has to be too heavy to shift or it will be shifted.
Tank mates are limited to fish too large to swallow and robust enough to hold their ground, and plenty of oscars end up alone or with one other oscar because that is what actually works. It is a fish that fills a room rather than a corner, and it is worth deciding on the space before deciding on the fish.
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