---
title: Flagfin Shrimpgoby (Mahidolia mystacina)
scientific_name: Mahidolia mystacina
common_name: Flagfin Shrimpgoby
taxon: Gobies
published: 2026-08-12T18:10:26.992Z
updated: 2026-08-12T22:09:48.344Z
tags: Flagfin Shrimpgoby, Mahidolia mystacina, Gobies, Red Sea, Marine Life, Diving
url: https://redseacreatures.com/taxon/fishes/bony-fishes/gobies/flagfin-shrimpgoby
---

# Flagfin Shrimpgoby (*Mahidolia mystacina*)

## Quick facts

- **Group:** Gobies (*Gobiidae*)
- **Size:** up to 8 cm
- **Depth:** 2-25 m
- **Diet:** Carnivore
- **Activity:** Diurnal
- **Rarity:** Uncommon
- **Habitat:** Silty sand and mud slopes, at a burrow shared with a shrimp
- **Reproduction:** Egg layer, Gonochoric

## How to recognise it

- tall first dorsal fin with a large dark blotch and a yellow margin, raised like a flag
- gray-brown body with pale bars and blue-white speckles on the cheek
- a shrimp working at the burrow entrance beneath it
- length up to 8 cm

A gray-brown goby with a big first dorsal fin it raises like a flag, dark-blotched and edged in yellow, on silty sand where the visibility is usually poor. Up to 8 cm (3.1 in), and permanently stationed at the mouth of a burrow it did not dig.

The burrow belongs to a snapping shrimp, and the arrangement is one of the best-known partnerships on the reef: the shrimp digs and maintains the tunnel for both of them, the goby stands guard. The shrimp is nearly blind, so it keeps one long antenna in contact with the fish at all times while it works, and a flick of the goby's tail sends both of them underground.

The signals are more specific than they look. Different tail movements mean approach, threat and retreat, the shrimp responds correctly to each, and pairings are consistent enough that particular goby species keep company with particular shrimp species. Neither animal does well alone: the shrimp will not leave a burrow without a partner, and the goby has no way to build one.

## Also known as

- **English:** Flagfin Prawn Goby, Smiling Goby
- **Japanese:** カスリハゼ, Kasurihaze
- **Russian:** Бычок-флаг

## Scientific synonyms

- *Gobius mystacina* Valenciennes, 1837
- *Gobius mystacinus* Valenciennes, 1837
- *Gobius pulverulentus* Kuhl & van Hasselt, 1837
- *Mahidiolia duque* Smith, 1947
- *Mahidiolia normani* Smith & Koumans, 1932
- *Mahidolia duque* Smith, 1947
- *Mahidolia mystacinus* (Valenciennes, 1837)
- *Mahidolia normani* Smith & Koumans, 1932
- *Mahidoria mystacina* (Valenciennes, 1837)
- *Waitea buchanani* Rao, 1972
- *Waitea mystacina* (Valenciennes, 1837)

## Range

Mozambique

---

*Source: [Red Sea Creatures](https://redseacreatures.com/taxon/fishes/bony-fishes/gobies/flagfin-shrimpgoby)*
*Updated: August 12, 2026*