The ocean is a vast and mysterious realm, home to an incredible diversity of life. Fish, with their varied forms and behaviors, are a significant part of this aquatic world. A common question is how many species of fish truly exist. Exploring this reveals the known biodiversity and the ongoing scientific effort to understand the ocean’s intricate ecosystems.
The Current Global Estimate
Scientists continually work to catalogue and understand marine life, providing current estimates for fish species in the ocean. Major scientific databases, such as FishBase, serve as central repositories for this information. As of February 2024, FishBase lists approximately 36,100 fish species. This number represents a compilation of described species, encompassing both marine and freshwater environments.
This figure is an estimate rather than a precise, fixed count. New species are regularly identified and described by researchers worldwide. On average, 300 to 500 new fish species are added to scientific records each year. For instance, the recent Ocean Census project announced the discovery of 866 new marine species, showing that the ocean’s biodiversity is still being uncovered.
Challenges in Quantifying Ocean Fish
Quantifying the exact number of fish species in the ocean presents significant obstacles for scientists. The vastness and inaccessibility of marine environments, particularly the deep sea and remote regions, make comprehensive exploration and sampling challenging. Much of the ocean remains unmapped and unexplored, limiting direct observation of its inhabitants.
Another challenge stems from “cryptic species.” These organisms appear morphologically identical but are genetically distinct and cannot interbreed. Identifying them often requires advanced genetic analysis, as subtle physical differences are not always apparent. What was once considered a single species might, upon closer inspection, be revealed as several distinct ones.
The process of classifying and naming species, known as taxonomy, is complex and subject to ongoing revision. As new data emerges, especially from molecular studies, species relationships are re-evaluated, leading to classification changes. Effectively sampling all marine environments is difficult and costly. Different sampling methods are often biased, meaning a combination of techniques is necessary to gain a complete picture of biodiversity.
Categorizing Marine Fish Species
When discussing “fish species” in the ocean, scientists refer to aquatic vertebrates categorized into three main classes based on their skeletal structure and evolutionary history. These categories clarify the diverse forms included in species counts.
The largest and most diverse group is the bony fish, known as Osteichthyes. This class includes most familiar fish species, such as tuna, cod, and clownfish, comprising about 96% of all fish. They are characterized by skeletons made of bone, and many possess a swim bladder for buoyancy control and an operculum covering their gills.
The second major group is the cartilaginous fish, or Chondrichthyes. This class includes sharks, rays, skates, and chimaeras, totaling around 1,100 to 1,200 known species. Unlike bony fish, their skeletons are made of cartilage. They have jaws, paired fins, and gill slits that open directly to the water.
Finally, the jawless fish, or Agnatha, represent the most primitive group. This small class, with 100 to 113 species, includes hagfish and lampreys. These ancient fish lack jaws and paired fins, and their skeletons are made of cartilage.