Humeral spot

Humeral spot is a distinctive marking found on the body of certain species of fish, particularly those belonging to the Characidae family, which includes tetras, piranhas, and their relatives. This spot is typically located on the humeral region, which is near the shoulder of the fish, just behind the gill cover and above the pectoral fin. The presence, absence, and appearance of the humeral spot can be significant in the taxonomy and identification of fish species within this family.

Characteristics

The humeral spot is often circular or oval in shape and can vary in color, usually being darker than the surrounding body coloration. Its size, shape, and color intensity may vary not only among species but also due to factors such as age, sex, and environmental conditions. In some species, the humeral spot is a key feature used by researchers and aquarists to distinguish between closely related species or to identify individuals within a species.

Function

The exact function of the humeral spot in fish is not fully understood, but several hypotheses exist. It may serve as a form of camouflage, helping the fish blend into its natural environment and evade predators. Alternatively, it could play a role in social communication or mating, acting as a visual signal to other members of the species. Some studies suggest that the spot could also be involved in intraspecific recognition, helping fish identify and associate with their own species.

Taxonomic Importance

In the taxonomy of Characidae and related families, the humeral spot is an important morphological feature. Taxonomists often use the presence or characteristics of the humeral spot, among other physical and genetic markers, to classify and differentiate species. Detailed descriptions of the humeral spot, including its position, size, and coloration, are commonly included in the scientific literature on fish taxonomy and systematics.

Examples

Several well-known aquarium fish exhibit a humeral spot, including:

• The Neon Tetra (Paracheirodon innesi), which has a bright blue horizontal stripe running along its body, complemented by a distinct humeral spot near the gill cover.
• The Black Phantom Tetra (Hyphessobrycon megalopterus), recognized by its semi-transparent body and a prominent humeral spot.
• The Serpae Tetra (Hyphessobrycon eques), which features a vibrant red body with a conspicuous humeral spot that aids in species identification.

Research and Conservation

Research on the humeral spot and its variations across different species contributes to our understanding of fish biodiversity, evolutionary relationships, and ecological interactions. Conservation efforts for freshwater habitats can benefit from such research, as understanding the specific needs and characteristics of species, including their identification through features like the humeral spot, is crucial for effective conservation planning and action.