The classification of aquarium fish is based on a precise hierarchical system, but the boundaries between taxa are shifting. Phylogenomic approaches regularly redraw the limits between genera and families, rendering some lists still circulated in the hobby obsolete. Correctly identifying a species requires cross-referencing stable morphological criteria with recent taxonomic revisions.
Phylogenomic Revisions and Impact on Aquarium Families
DNA analyses have caused major reshuffles in several common families in aquaristics. The Cyprinidae, long considered a monolithic group, have been split into distinct subfamilies. Some genera of barbs that were once grouped under the same taxon are now separated by significant genetic distances.
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The description of new genera is actively ongoing. A recent example, published in ZooKeys in August 2026, illustrates this dynamic: new taxa continue to be described each year, which alters the phylogenetic trees we rely on to classify our inhabitants.
For the aquarist, the direct consequence is practical. A fish sold under a given genus name may have been reclassified. The Callichthyidae provide a good example: the genus Corydoras has been subdivided, and several popular species now bear a genus name different from that on the retailer’s label. Consulting the sheets classified by family on My Fish Book allows for a quick check of the current taxonomic positioning of a species before purchase.
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Reliable Morphological Criteria for Identifying a Fish Family
The fin formula remains the most robust identification criterion for distinguishing families in freshwater aquaristics. The number of hard and soft rays, their relative position on the body, and the presence or absence of certain fins (such as adipose) are stable markers that genetics confirms in the vast majority of cases.
We recommend proceeding by elimination by observing three areas of the body:
- The mouth and dentition: a protractile jaw points towards the Cichlidae, pharyngeal teeth towards the Cyprinidae, and visible conical teeth towards certain Characidae.
- The adipose fin: its presence indicates a Characiform or Siluriform. Its absence eliminates these orders outright.
- The type of scales and skin covering: bony lateral plates characterize the Loricariidae, bare or nearly bare skin the Siluridae, and ctenoid scales most Perciformes.
These criteria work better than identification by color or pattern. Colors vary according to stress, maturity, and maintenance conditions, while the fin formula and mouth structure remain constant in adults.
Key Families in Tropical Freshwater: What Morphology Doesn’t Always Reveal
Some families present recurring identification difficulties in community tanks. The Osphronemidae (broadly, gouramis) and Anabantidae are distinguished by the presence of a labyrinth organ, but confusion between genera remains common in the trade. A Trichopodus and a Trichogaster superficially resemble each other, while their water volume needs and territorial behavior differ significantly.
Within the Cichlidae, internal diversity further complicates the task. A cichlid from Lake Malawi and an Apistogramma have almost nothing in common in terms of water parameters, reproductive behavior, and diet, despite belonging to the same family. We regularly observe cohabitation errors related to this confusion.
The case of the Characidae is comparable. The neon (Paracheirodon innesi) and the red piranha belong to the same order, but the subfamily and lifestyle diverge radically. Classifying by family is not enough: descending to the genus level, or even species, remains the only reliable approach to determine tank compatibility.
When Behavior Complements Morphology
The swimming mode provides an additional clue. Schooling fish (most small Characidae and Cyprinidae) adopt synchronized movement in groups. An isolated individual swimming alone in open water rarely points towards a Loricariinae or a benthic Siluriform.
Reproductive behavior often confirms family affiliation. Open substrate spawners, mouthbrooders, bubble nest builders: each strategy is correlated with specific families. A fish that builds a bubble nest at the surface almost systematically belongs to the Osphronemidae or Belontiidae.
Current Identification Tools for the Aquarist
Classic visual identification remains relevant, but new tools complement the approach. AI-assisted classification systems, based on the analysis of phenotypic traits (body shape, color pattern, proportions), are beginning to be used to identify species from photographs.
These tools do not replace basic taxonomic knowledge. They serve as a first filter, particularly useful for uncommon species encountered at fairs or in direct imports. Cross-referencing AI identification with manual morphological verification limits errors.
Online databases remain the foundation. They allow tracing from species to genus, then family, while checking synonymy and any recent reclassifications. When a scientific name seems no longer to correspond to current descriptions, it is often because a taxonomic revision has taken place in the meantime.
The classification of aquarium fish is not a fixed exercise. Genomic revisions will continue to alter the contours of the families we use daily. Mastering basic morphological criteria and keeping up with taxonomic updates remains the safest way to avoid identification errors, and by extension, maintenance errors.