---
title: Sidespot Cardinalfish (Apogonichthyoides heptastygma)
scientific_name: Apogonichthyoides heptastygma
common_name: Sidespot Cardinalfish
taxon: Cardinals
published: 2024-11-08T12:50:41.883Z
updated: 2026-08-19T10:00:54.195Z
tags: Sidespot Cardinalfish, Apogonichthyoides heptastygma, Cardinals, Red Sea, Marine Life, Diving
url: https://redseacreatures.com/taxon/fishes/bony-fishes/cardinals/sidespot-cardinalfish
---

# Sidespot Cardinalfish (*Apogonichthyoides heptastygma*)

## Quick facts

- **Group:** Cardinals (*Apogonidae*)
- **Size:** 3.3 cm
- **Diet:** Carnivore
- **Activity:** Nocturnal
- **Rarity:** Rare
- **Habitat:** Sheltered reef and rubble
- **Reproduction:** Mouthbrooder
- **Endemic:** Endemic to the Red Sea

## How to recognise it

- just over three centimeters, brown, deep-bodied
- single dark blotch on the side, below the middle of the body
- dark bar through the eye
- up to 3.3 cm

Three and a bit centimeters, brown, and it lives in this sea and nowhere else.

What separates it from its close relatives is a single dark blotch on the side of the body and its position relative to the lateral line. That is the whole diagnosis. Change the light, photograph it at a slight angle, catch it as a juvenile, and the difference is gone.

This is the ordinary condition of small fish taxonomy and it is worth being honest about. A large part of the catalogue rests on characters at this scale, and where a group is small, brown, nocturnal and cryptic, the species boundaries are drawn by a handful of specialists working with preserved material, and they move. Fish that were one species become three; three become one.

So a record of this animal from a photograph should be read as probable rather than certain, and the same caution applies to a good many small cardinalfish, gobies and blennies on this site.

It is rare in the records, which for a three-centimeter nocturnal fish in rubble means very little indeed.

## Also known as

- **Czech:** parmovec sedmiskvrnný

## Scientific synonyms

- *Apogon enneastigma* Rüppell, 1838
- *Apogon heptastigma* Cuvier, 1828
- *Apogon heptastygma* Cuvier, 1828
- *Ostorhinchus heptastygma* (Cuvier, 1828)
- *Ostorhynchus heptastigma* (Cuvier & Valenciennes, 1828)

---

*Source: [Red Sea Creatures](https://redseacreatures.com/taxon/fishes/bony-fishes/cardinals/sidespot-cardinalfish)*
*Updated: August 19, 2026*