Compatibility Overview
Firefish Goby and Molly are generally not recommended to be housed together. The issues listed above — whether water parameter incompatibility, predation risk, or aggression — create conditions where one or both fish are likely to suffer harm or chronic stress.
| Factor | Firefish Goby | Molly | Verdict |
|---|---|---|---|
| Temperature | 72–81°F | 72–82°F | ✅ 72–81°F |
| pH Range | 8.1–8.4 | 7.5–8.5 | ⚠️ 8.1–8.4 (narrow) |
| Temperament | semi | peaceful | ⚠️ Monitor |
| Adult Size | 1.2 in | 4 in | ⚠️ 3.3× difference |
| Min. Group | 1+ | 3+ | See below |
| Min. Tank Size | 55 gallons (for both species) | — | |
✅ Compatibility Positives
❌ Incompatibility Reasons
Species Profiles
Firefish Goby — Aquarium species
The Firefish Goby is a popular choice for saltwater aquariums due to its vibrant colors and peaceful nature. These goby fish thrive in well-maintained tanks with plenty of live rock for them to explore. They are best kept in pairs or small groups and can be a great addition to a community tank with compatible species. It's important to provide them with a sp
→ Full Firefish Goby care guide
Molly — Poecilia sphenops
Hardy livebearers that prefer alkaline, hard water — sometimes slightly brackish. Prolific breeders; peaceful community fish.
Frequently Asked Questions
Can Firefish Goby live with Molly?
Generally not recommended. Firefish Goby and Molly are generally not recommended to be housed together. The issues listed above — whether water parameter incompatibility, predation risk, or aggression — create conditions where one or both fish are likely to suffer harm or chronic stress.
What tank size do I need for Firefish Goby and Molly together?
A minimum of 55 gallons is recommended for keeping Firefish Goby and Molly together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Firefish Goby and Molly?
72–81°F
Is a Firefish Goby aggressive toward a Molly?
Firefish Goby is semi and Molly is peaceful. These animals require different water types and cannot share one aquarium.
Related Compatibility Guides
Compatibility score breakdown
The overall score is weighted across water chemistry, behavior, adult size, swimming zone, and social needs. A score is a planning aid—not a guarantee for individual fish.
| Factor | Score |
|---|---|
| Temperature | 100/100 |
| Ph | 100/100 |
| Temperament | 75/100 |
| Adult Size | 38/100 |
| Swim Zone | 92/100 |
| Social Needs | 92/100 |
Tank size scenarios
Use the scenario that matches the actual group sizes and temperament you plan to keep.
| Scenario | Tank | When it applies |
|---|---|---|
| Minimum viable | 55 gal | Only for the recommended minimum groups, mature filtration, and close monitoring. |
| Recommended community | 75 gal | Adds territory, swimming room, and a safer buffer for behavior. |
| Low-conflict setup | 125 gal | Best when keeping larger schools or reducing territorial pressure. |