Bluespotted Jawfish, Opistognathus rosenblatti
Bluespotted Jawfish, Opistognathus rosenblatti. Underwater photograph taken in Zihuantanejo Bay, Guerrero, December 2019. Photograph and identification courtesy of Maude Jette, Dive Zihuantanejo, www.Divezihuatanejo.com.
The Bluespotted Jawfish, Opistognathus rosenblatti, is a member of the Jawfish or Opistognathidae Family, that is also known as Rosenblatt’s Jawfish, and in Mexico as bocón manchas azules. Globally, there are forty-three species in the genus Opistognathus, of which thirteen are found in Mexican waters, six in the Atlantic and seven in the Pacific Ocean.
The Bluespotted Jawfish has an elongated, compressed, and tapered body with a large bulbous head. They are dark brown in color with large electric blue spotting and a yellow dorsal fin. They are dimorphic with breeding males being white anteriorly and darker posteriorly. The juveniles are a uniform yellow, covered with smaller blue spots. The head has large eyes set high, a large mouth without teeth and no cirrus. Their anal fin has 3 spines and 13 or 14 rays; their caudal fin is rounded; their dorsal fin has 11 spines and 13 or 14 rays, and, their pectoral fins have 17 or 18 rays. They have 34 or 35 gill rakers. They are covered with small smooth scales. Their lateral line is limited to the the first half of their body.
The Bluespotted Jawfish is found in sandy or rubble substrate within inshore shallow water at depths up to 25 m (82 feet) in large well-spaced colonies of several hundred individuals. They spend almost their entire life in dug out burrows that they cover at night and rebuild each morning. These elaborate burrows are self-constructed by utilizing their mouth and powerful jaw to excavate sand, small stones, and medium-sized rocks. They only exit the burrows to mate. They reach a maximum of 10.0 cm (3.9 inches) in length. They consume zooplankton that is removed from passing water. In addition, like other jawfish, they are mouth brooders exhibiting the unusual habit of oral egg incubation that hatch in five to seven days. The Bluespotted Jawfish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Bluespotted Jawfish is a resident of Mexican waters of the Pacific but has a limited distribution, being found in the southern half of the Sea of Cortez and small isolated populations along the coast of the mainland. The fish photographed above represent a southerly extension of the known range for this fish.
The Bluespotted Jawfish is straightforward to identify and cannot easily be confused with any other jawfish due to the prominent blue spots on the head and body.
From a conservation perspective, the Bluespotted Jawfish is currently considered to be of Least Concern with stable, widely distributed populations. They are small in stature and seldom seen by humans. They are utilized by the aquarium trade at a nominal level due to their exceptional beauty but require large spaces with ample hiding places, a cold-water environment and are not often visible as they spend the majority of their time in their burrows.