Cobalt Blue Goby - Stiphodon semoni Fish Profile & Care Guide
Introduction
The stunning Cobalt Blue Goby (Stiphodon semoni) is a gentle, small-bodied stream goby that spends most of its time rasping algae and biofilm from rocks, with adult males often developing striking blue-green tones when kept in a suitable setup. These Gobies are not true "shoaling" fish, but they do settle better when kept in a small group where they can spread out and establish a loose social hierarchy. In groups, you will usually see more natural behaviour: males display to one another, hold small perching territories, and posture rather than constantly hiding. This social side comes with a catch: mature males can be territorial with rivals in tight spaces, so a bigger footprint, broken sight-lines, and multiple grazing areas make a noticeable difference to how peaceful the group feels.
Choose tankmates that are calm, non-predatory, and comfortable in high-oxygen, high-flow conditions. Peaceful midwater fish that do not harass the bottom zone are usually ideal, along with small, non-aggressive invertebrates if you are keeping a shrimp-friendly setup. Avoid anything boisterous or territorial that will claim the same rockwork, and avoid larger fish that may view a small Goby as food. Also, be mindful of "competitive grazers". If you keep other strong algae and biofilm feeders, make sure there is enough natural growth and supplementary food so S. semoni is not outcompeted at feeding time.
For Cobalt Blue Gobies, recreate a river-style setup with smooth stones, rounded cobbles, and lots of hard surfaces where biofilm can build up, along with calmer, sheltered areas for resting. Use strong filtration and steady flow to maintain high oxygen levels and keep the water exceptionally clean, as they naturally come from pristine running streams. Most keepers aim for temperatures in the low to mid-20s Celsius, with a near-neutral to slightly acidic pH, and support this with regular water changes to prevent nitrate and waste levels from rising.
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Photos
Sexual Dimorphism
Sexing Cobalt Blue Gobies becomes easier as they settle in and colour up. Mature males are typically more intensely coloured (often vivid blue-green in this species), with a more "showy" look during displays, while females usually remain plainer and more subtly patterned. Behaviour helps too: males are more likely to posture, flare their fins, and hold preferred perching spots, especially when another male is in view. Because colour and confidence are strongly tied to environment, diet and stress levels, a subdued male can look female at first - once conditions are right, the difference usually becomes much clearer.
Quick Facts
| Scientific Name | Stiphodon semoni |
|---|---|
| Year Described | 1895 |
| Other Names | Blue Stiphodon Goby |
| Kingdom | Animalia |
| Classification | Actinopterygii |
| Order | Gobiiformes |
| Family | Oxudercidae |
| Genus | Stiphodon |
| Origins | Indonesia Papua New Guinea Philippines Solomon Islands |
| Approx Max Size | 5 cm |
| Temperament | Peaceful |
| Aquarium Level | All Levels |
| Difficulty | Beginner - Intermediate |
| Shoaling | NA |
| Best kept as | 3 Females per Male |
| Diet & Feeding | Omnivore |
| Reproduction | Egg Depositor |
| Average Lifespan | Up to 5 Years |
Water Parameters
| Water Type | Freshwater |
|---|---|
| pH | 6.5 - 7.5 |
| GH | 2 - 12 |
| KH | 2 - 6 |
| TDS | 36 - 215 |
| ℉ | 68 - 82 |
|---|---|
| ℃ | 20 - 28 |
Natural Habitat
The Cobalt Blue Goby originates from the western Pacific, including Indonesia, New Caledonia, Papua New Guinea, the Philippines, and the Solomon Islands, and is typically found in clear, shallow tropical streams, particularly the fast-flowing stretches just upstream of waterfalls. These stretches are highly oxygenated and usually dominated by exposed bedrock with scattered cobbles and boulders rather than sand or dense plant growth. Under the bright, shallow conditions, the rocks develop a thick coating of aufwuchs - a nutritious mix of biofilm, algae, and microorganisms that the gobies spend much of their time grazing. Streamside vegetation overhangs the banks and gradually contributes leaf litter to the water, adding a natural, lightly "woodland stream" feel without turning it into a planted habitat.
Breeding
Like many Stiphodon, the Cobalt Blue Goby have an amphidromous life cycle: adults live and spawn in freshwater; the eggs will hatch, and the larvae drift downstream to the sea; then the young return upriver later as juveniles. This is the main reason successful breeding through to juveniles is rare in a standard freshwater community aquarium - the larvae are adapted to develop in marine conditions for an extended period before returning upstream. In other words, you may see courtship and even eggs, but raising fry typically requires a specialised approach, including planned larval collection, a controlled transition into marine conditions, and appropriately tiny first foods.
Diet & Feeding
The Cobalt Blue Goby is primarily an aufwuchs (biofilm) grazer, it scrapes microalgae, diatoms and the tiny organisms living within that film from rocks and other hard surfaces. In aquariums that are "too clean" or newly set up, the most significant risk is slow starvation, because there isn't enough established grazing to meet their needs. A mature tank with light-grown stones and wood is a major advantage, and you will usually see them working the same surfaces all day rather than charging into open-water feeding. When you do supplement, think in terms of foods that mimic their natural intake: small-particle sinking foods and gel or paste-style algae diets tend to work better than large pellets or floating foods, and offering tiny portions more often is generally more effective than one big feed that sinks and gets lost in the substrate.
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Published: 06 Feb 2026
Last Updated: 06 Feb 2026