How many fish can live together safely?
Written by
John Williams
Reviewed by
Prof. David Walsh, Ph.D.Tank stocking limits differ by species, not just size. Cramming too many into one tank stresses them out and leads to aggression and disease. Some fish should be alone or in pairs. Others need to swim in groups. Others may need more space than others, or caps may be preferable. Striking a balance requires effort, intuition, biology, and knowledge. Your aquarium is best when it contains natural nuances.
Schooling Requirements
- Tetras need 6+ members for security
- Rasboras require 8+ to prevent stress
- Barbs form hierarchies in groups of 5+
Territorial Space Needs
- Cichlids require 30+ gallons per pair
- Betta fish need personal zones
- Gouramis claim surface territories
Biological Load Limits
- Goldfish produce heavy waste needing 20+ gallons
- Plecos require strong filtration systems
- Oscars need oversized filters for their growth
Some fish species are "schooling species." Neon Tetras require at least six in their school. With fewer than six people, it will be stressed and "lose its colour." However, in larger schools, it has been shown to exhibit natural behaviours. Rasboras are believed to need eight, while cedar and tiger Barbs live in schools of five and develop a hierarchy within them. Before buying in groups, aim for the minimum required number for your species.
Territorial Fish require their own space: cichlids want thirty gallons per pair; they set up breeding areas; bettas want a space they can claim on the surface; gouramis defend a floating plant spot; give them some screens, some places to hide, and you will get constant fighting among them if your tank is at all overcrowded.
Tank Sizes. Must correspond to swimming habits. Animated danios require long tanks. Surface swimmers want space for swimming on the surface. Bottom fish need room on the floor; deep tanks waste space for horizontal swimmers. The adults, not the young, should be measured. There should be space for swimming naturally.
Biological limits that prevent you from poisoning yourself during the process. Goldfish, as discussed, produce loads of muck and need twenty gallons worth each to make them all happy. Plecos need ridiculous over-filtration. Oscars grow so rapidly that they require a filter upgrade about once a month. Check your water weekly for ammonia spikes and upgrade your filtration at least a week before adding fish.
Make the inch-per-gallon rule workable. It doesn't work for big, messy fish. You'll want three gallons per inch for goldfish, two for cichlids. Reduce stocking by twenty percent for juveniles. The swimming room always takes precedence over numbers.
Read the full article: Fish Compatibility Chart Ultimate Guide
