AquariumStocking

What Size Tank Does a Jack Dempsey Need?

Footprint first: a Jack Dempsey needs swimming length and width before gallons matter.

Full breakdown: freshwater fish size and tank data.

Quick answer: Seriously Fish lists the Jack Dempsey (Rocio octofasciata) at up to 8 in. standard length and recommends a tank base of at least 48 × 18 in. for one adult pair, at 68 to 86 °F and pH 6.5 to 8.0. Aqueon's standard 75 gallon tank measures 48½ × 18½ in. across the base, so it meets that footprint.

Check a tank against the 48 × 18 in. base

Jack Dempsey facts

FigureValue
Max standard length8 in. (200 mm)
Minimum tank base48 × 18 in. (120 × 45 cm), for one adult pair
Temperature68–86 °F
pH6.5–8.0

Source: Seriously Fish, Rocio octofasciata profile.

Standard tanks against that base

Aqueon tankBase (L × W)48 × 18 in. base
29 gallon30¼ × 12½ in.Too short and narrow
40 Breeder36³⁄16 × 18¼ in.Too short
55 gallon48¼ × 12¾ in.Too narrow
60 Breeder48½ × 18½ in.Meets
75 gallon48½ × 18½ in.Meets
90 gallon48½ × 18½ in.Meets
125 gallon72½ × 18½ in.Meets

Tank bases: Aqueon critical dimensions. A tank meets the footprint when it is at least 48 in. long and 18 in. front to back.

What this means

A 55 gallon tank is long enough at 48¼ in. but only 12¾ in. front to back, so it misses the 18 in. width. The 75 gallon meets both, and so do the 60 Breeder and the 90. For more on a 4 ft tank, see how many fish in a 75 gallon tank and what size heater for a 75 gallon tank.

Comparing cichlids? The oscar needs a larger 60 × 24 in. base, and angelfish a smaller 39 × 16 in.

Sources

Compiled with AI assistance from the sources below. Spot an error? Email jpanasuk@gmail.com.