We Analyzed 1,275 Aquarium Fish: The Data on Difficulty, Temperament & Saltwater vs Freshwater
We analyzed care data for 1,275 aquarium fish species. Saltwater fish are 3.5× harder than freshwater, most species are peaceful, and more — the full data study.
How hard is the average aquarium fish to keep? Are most species peaceful or aggressive? And is saltwater really that much harder than freshwater — or is that just hobby folklore?
To find out, we analyzed the care profiles of 1,275 aquarium fish species in the Studio Scaped database. Below are the findings, along with the full methodology so you can check our work — and cite it.
Key findings
- 71% of aquarium fish species are freshwater, 27% are saltwater, and the remaining ~2% are brackish or move between environments.
- Most aquarium fish are peaceful. 52% are peaceful, 35% are semi-aggressive, and only 13% are outright aggressive.
- Only 28% of species are genuinely beginner-friendly (rated Beginner or Easy). Nearly half (46%) are Intermediate, and 26% are Advanced or Expert.
- Saltwater fish are ~3.5× harder to keep than freshwater. 53% of saltwater species require advanced or expert care, versus just 15% of freshwater species.
- Freshwater is nearly twice as peaceful. 61% of freshwater species are peaceful, compared with only 32% of saltwater species.
1. Freshwater dominates the hobby
Across all 1,275 species, freshwater fish make up the clear majority.
| Water type | Species | Share |
|---|---|---|
| Freshwater | 899 | 71% |
| Saltwater (marine) | 349 | 27% |
| Brackish | 14 | 1% |
| Mixed / other | 13 | 1% |
2. Most fish need more than beginner-level care
The single most common difficulty rating is Intermediate — the "average" aquarium fish is not a beginner fish.
| Difficulty | Species | Share |
|---|---|---|
| Beginner / Easy | 359 | 28% |
| Intermediate | 581 | 46% |
| Advanced | 290 | 23% |
| Expert | 45 | 4% |
Put together, only just over a quarter (28%) of aquarium fish are truly beginner-appropriate — a useful reality check for anyone stocking their first tank.
3. The saltwater difficulty gap is real
This is the clearest pattern in the data. Splitting difficulty by water type shows saltwater fish are dramatically more demanding:
| Beginner / Easy | Advanced / Expert | |
|---|---|---|
| Freshwater (n=899) | 33% | 15% |
| Saltwater (n=349) | 16% | 53% |
More than half of all saltwater species need advanced or expert-level care, versus 15% of freshwater species — roughly a 3.5× difference. If you're new to the hobby, the data strongly supports the conventional advice: start in freshwater.
4. Temperament: peaceful overall, but it depends on the water
Most aquarium fish are peaceful — but that headline hides a big split between freshwater and saltwater.
| Temperament (all species) | Share |
|---|---|
| Peaceful | 52% |
| Semi-aggressive | 35% |
| Aggressive | 13% |
Broken down by water type, freshwater communities are far more peaceful, while saltwater species skew heavily semi-aggressive:
- Freshwater: 61% peaceful, 17% aggressive.
- Saltwater: 32% peaceful, and a striking 66% semi-aggressive.
In other words, the "peaceful community tank" is much more of a freshwater phenomenon. Saltwater tanks require more careful attention to territory and stocking order.
What this means for fishkeepers
- New to the hobby? The odds are in your favour with freshwater: a third of freshwater species are beginner-friendly and 6 in 10 are peaceful.
- Considering saltwater? Go in with your eyes open — the majority of marine species are advanced-plus and semi-aggressive. It's rewarding, but it's not where most people should start.
- Building a community tank? "Peaceful" is the most common temperament, but always check individual species — 48% are not fully peaceful.
You can explore the underlying data yourself: browse all freshwater fish, all saltwater fish, or the full fish care database and tank-mate compatibility guides.
Methodology
We analyzed the structured care data for 1,275 aquarium fish species documented on Studio Scaped. Every species in the dataset has a recorded water type, difficulty rating, and temperament, so the distributions above cover the full set (no missing-data gaps for these fields). Difficulty and temperament are expert-assigned categorical ratings; where labels varied in spelling or case (e.g. "Semi-aggressive" / "Semi-Aggressive"), we normalised them into single categories before counting. Percentages are rounded to the nearest whole number, so columns may not sum to exactly 100%.
Limitations. Ratings reflect typical care requirements and temperament for each species and are not a substitute for researching an individual fish. This is a snapshot of the species we currently document, not every fish in the trade.
Cite this study
Findings and data are free to use with attribution. Please credit Studio Scaped and link to this page:
Studio Scaped (2026). We Analyzed 1,275 Aquarium Fish: The Data on Difficulty, Temperament & Saltwater vs Freshwater. https://www.studioscaped.com/blog/aquarium-fish-data-study
Writing about beginner fish, freshwater vs saltwater, or fish temperament and want a specific cut of the data? Get in touch — we're happy to share.
