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Related Articles: The Blue-Spotted Jawfish, Opistognathus rosenblatti, A Cool Fish in More Than One Sense by Bob Fenner, Jawfishes by Bob Fenner, Jawfishes for Small Marine Systems by Bob Fenner, The Pearly or Yellow or Golden-headed Jawfish, Opistognathus aurifrons, Use in Marine Aquariums by Bob Fenner,  

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FAQs on: Blue-Spotted Jawfish Identification, Blue-Spotted Jawfish Behavior, Blue-Spotted Jawfish Compatibility, Blue-Spotted Jawfish Stocking/Selection, Blue-Spotted Jawfish Systems, Blue-Spotted Jawfish Feeding, Blue-Spotted Jawfish Disease/Health, Blue-Spotted Jawfish Reproduction, Jawfishes 1, Jawfishes 2, Jawfish Identification, Jawfish Behavior, Jawfish Compatibility, Jawfish Selection, Jawfish Systems, Jawfish Feeding, Jawfish Disease, Jawfish Reproduction,
Jawfishes for Small Marine Systems by Bob Fenner,  

The Blue-Spotted Jawfish, Opistognathus rosenblatti,

A Cool Fish in More Than One Sense


 Bob Fenner

At the Birch, SIO 

Due to the relative age of the marine aquarium hobby, and my'¦ long involvement, there are several species of saltwater organisms that I'm familiar with from their inception of use as ornamentals. One of these is the subject of this article; the spectacular Blue-Spotted Jawfish. As a matter of fact, I had the experience of diving and seeing this fish in the early seventies, years before its original scientific description (by Gerald Allen and D. Ross Robertson in 1991). Due to its rather limited range and on and off again collection and transport limitation out of Mexico, Rosenblatt's Jawfish has had a spotty, punctuated presence in the hobby. At times a few will come in, even go on display in Public Aquariums with "tropical" Eastern Pacific displays, but the Blue-Jaw has two major strikes against it'¦ all to do with its necessary environment. This fish needs a good deal of dedicated space, and really a chilled setting to do well. Herein lays my tale of Opistognathus rosenblatti.

The Blue-Spotted Jawfish, Opistognathus rosenblatti, Allen & Robertson 1991, of Mexico's Sea of Cortez (Gulf of California in older, less PC texts) is a real striker, with brilliant blue dots over its overall dark brownish body. The males become bright white in the front half of their bodies during spawning and courtship. To six inches total length. Named in honour of Richard/Dick Rosenblatt of the Scripps Institute of Oceanography, an early (1960's) collector of the species in Mexico.


Distribution & Habitat:

This fish is found in sandy (not really adjacent to rock) bays and open ocean areas from about the middle of Baja Mexico's Sea of Cortez, down to the tip (Los Arcos), which is where I first encountered it (Cabo San Lucas, at the Playa del Amor'¦ the "Beach of Love"), in 30 to 90 foot depths. The species is unmistakable in terms of coloration, markings and behavior. Juveniles are uniformly colored yellow with blue spots, females with dark-brown bodies and larger blue spots, and courting males being stark white in their anterior halves, blackish posteriorly during displays.


This is a very social species, with several individuals living about evenly spaced a meter apart from each other in offshore sandy areas in open ocean and bays, living almost entirely within their dug out burrows. Unlike the commonly available member of the family, the Pearly Jaw of the Atlantic (Opistognathus aurifrons) which spends a good deal of time out and above their burrows year long in the wild, O. rosenblatti males only display during warm weather (summer months), when competitions for females include a change in colour and hovering a few feet above their burrow openings.


Due to their secretive life history, this fish is best kept w/o other fishes, and very little else in the way of livestock. They live in very open sandy or rubble areas, not necessarily near rocky reefs, with only occasional other fish swimming nearby. If you want to see yours any percentage of the time, maintain it/them in a dedicated set-up. If you do opt for other life presence, make sure it is easy going, slow-moving and not too competitive in feeding with your Jaw/s.


This whole family ships exceptionally well, and the Blue-spot is almost always exemplary on arrival. Other than waiting for a day or so to see if the fish will die mysteriously, I would not leave this species at a dealers for any more time, nor would I quarantine this or any other Opistognathid. There's far more to be lost than gained in such delays; with stress and the very real possibility of the fish damaging themselves vs. the small likelihood of advancing biological disease.


The size and shape of a system to suit the Blue-spot almost always goes unaccommodated by aquarists. Though this fish is small (most specimens are sold at 4-5" overall length) it really requires a large area of open expanse, AND width to feel comfortable. How much dimensionally? A good three feet of width between specimens and two foot plus in width of a good deal of mixed fine sand and rubble substrate. This last should be a good eight inches'¦

Now you say, "But I've seen/known other folks who have kept this Jawfish in smaller settings, crowded even with other fishes'¦". Maybe they were lucky, and very likely their Blue-Spot did not live very long or well.

As if the call for grand size systems with none to few roommates, and bunches of sand wasn't enough, these fishes are not really tropical animals. That's right, they live in cooler water. The Eastern Pacific coast receives as part of the North Pacific Gyre (remember the Coriolis Effect?) the California Current off the coast of the United States and Mexico's two States/Estados of that name'¦ this is cold water propagating from the north (as in Alaska) down to about the equator, where it takes a gliding western turn, going back up north generally in the now much warmer Western Pacific Ocean as the Japanese Current. The practical implication is that water off the Californias is appreciably cooler than the same latitudes in the W. Pacific, with the habitat of the Blue-Spotted Jaw being mostly in the upper 50's F. to upper 60's, and rarely lower 70's F'¦. Brrr? Yes. Being an old/er timer in this interest, including the hobby, trade and sciences, I have seen a few cycles of cool to colder water organisms sold, or may I state, mis-represented as tropicals (Catalina Gobies, Garibaldi, Metridium and Tealia Anemones, Moon Snails, many types of Algae'¦)'¦ These won't live for long in too-warm surroundings and neither will this cool water Jawfish. Soooo, if you live in most anywhere you don't have to wear coats and sweaters, you will likely need to buy and run a chiller to keep this fish long-term.


There are Jawfish species that have a broader diet, consuming worms, crustaceans et al. infaunal material; the Blue-Spot is almost exclusively a zooplanktivore, looking for and snapping small animals in the water column as they float or drift by over their immediate territory. Ideally, you might have a good-sized refugium attached to your main display tank with the Jaw/s'¦ with a RDP (Reverse Daylight Photoperiod) arrangement for lighting it during the "off times" for the Jaw system. As much of the life in vibrant, established refugiums is nocturnal, some of this will be swept up and delivered to the main system on a periodic basis. Alternatively, providing small whole or cut up meaty foods into a jet/pump discharge a few times a day will work.


Small scales are not a problem as with other fish families where parasitic and infectious diseases are concerned. Jawfishes are remarkable in holding out as last to near last contractors of such, and typically don't suffer easily for treatment with the generally toxic to outright poisonous constituents of "fish remedies". Nonetheless, I urge you to take care in treating these and all other fishes with formalin, dyes like Malachite Green and metal salt solutions (e.g. Copper based medications); and instead opt for quinine compounds (e.g. Chloroquine Phosphate) if you find yourself having to treat for Protozoan complaints.


Kerstitch (1979) reports the Blue-Spotted Jawfish to be a mouthbrooder like its common congener the Yellow-head of the Atlantic. Males display behaviorally and colour-wise in the summer months, dashing 3-4 feet above their burrows, trying to attract a female. If successful the female joins the male in his tube for a few minutes, emerging to return to her own. Further details on length of incubation, time spent as planktonic larvae, foods taken et al. was not found. I presume the time et al. may be similar to O. aurifrons, as very small young have been observed post-settled.


I suspect all who read this brief report will grasp the salient needs of keeping this species in captivity. SPACE! Even just one specimen needs several tens of gallons of volume to feel comfortable. Secondly, this is a very social species that only exhibits well in the presence of conspecifics, necessitating providing a good yard/meter of space between each specimen. Further, such space needs to be two-dimensional, i.e. wide as well as long, to allow the Blue-Jaw reasonable security that it can 'get away' from whatever approaches the viewing panel of the system. Lastly, this is not really a tropical fish, but a cooler to temperate species that often requires a chiller in use to keep its water sufficiently low in temperature.

The reality is that O. rosenblatti is far from being a "good choice" for most hobbyists as an aquarium species; and that aquarists are better redirected to keeping more suitable members of the family Opistognathidae, like the "standard" Pearly or Goldenheaded Jawfish, O. aurifrons of the tropical West Atlantic.

Bibliography/Further Reading:

Allen, G.R. and D. Ross Robertson 1994. Fishes of the tropical eastern Pacific. University of Hawaii Press, Honolulu. 332 p.

Fenner, Robert. 1996. Jawfishes. TFH 8/96.

Fenner, Robert. 1998. The Conscientious Marine Aquarist. Microcosm, VT. 432pp.

Kerstitch, Alex. 1979. The first record of the courtship behavior of the Blue Spot Jawfish. FAMA 9/79.

Kerstitch, Alex. 1988. Master builders (re the family). SeaScope Winter 88.

Michael, Scott. 2000. The whimsical Jawfishes. AFM 8/00.

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