Assessing Macneil's Assessor

Assessor macneilli is a small fish from the western Pacific and East Indian Oceans. They are most commonly found in the shallow tropical seas around Australia and New Caledonia, where they live in groups in caves and under ledges. They are generally uniformly dark blue with a lighter, neon blue fringe to their fins and occasionally around their eyes and mouth. They have a very unique habit of living “upside down” most of the time, adding a dimension of interest to the home aquarium. They can seemingly cling to the bottom of overhanging rocks and the tops of caves. In North America these fish are most often called “Blue Assessors” or “Macneil's Assessors.” Internationally they are also commonly called “Squatters,” “Blue Scissortails” and Blue Devilfish, though this last name is hardly warranted most of the time.

Of all the Assessors, the Macneil's Assessor is probably the most docile, being a peaceful tankmate to pretty much everything that isn't another Assessor. While they are frequently found grouped up in the wild, it captivity we don't recommend it, unless there is ample tank space for them to escape each other. Because they rarely get bigger than two or three inches long, A single Macneil's Assessor can be kept quite happily in an aquarium as small as 30 gallons. Those of you wishing to keep a small group of them would do better in tanks that were 110 gallons or bigger, with an emphasis on length instead of height. They are generally model citizen in all reef tanks though they do prefer lower light scenarios, and are more likely to be reclusive in very brightly lit aquariums. In any aquarium, there should be ample rockwork for them to hide in, and a large overhang somewhere would mimic their natural habitat, giving them the opportunity to display their most eccentric habit of upside down life.

Macneil's Assessors are occasionally available aquacultured, though they generally have very small brood sizes and as such are difficult as a commercial enterprise. They are mouthbrooders, with the male carrying the small clutch of eggs, until they hatch into plankton. Spawning and reproduction has been carried out by diligent hobbyists, though as of writing this, there haven't been many reports of success in rearing the fry to adulthood. If interested in attempting this, buying one larger fish and a few smaller specimens all at once will aid both in preventing some aggression, and in the likelihood of creating a harem as the males are generally larger than females. Watch this introduction carefully as the Assessor macneilli is a reclusive fish at first and more timid specimens could suffer from missing meal times if being bullied overmuch.

Husbandry of the Macneil's Assessor is very straightforward and they are an easy fish to keep. They will readily take a variety of small meaty and prepared foods without much work. They are hardy, peaceful, interesting and make great additions to reef tanks as they are very unlikely to be a problem for sessile invertebrates. While this makes them an ideal fish for beginning hobbyists, their unique and humorous swimming style also makes them an interesting addition to the tanks of more veteran fish keepers. Water quality parameters are the same as just about everything else you're interested in keeping so why not give Macneil's Assessor a try in your own tank? Ask your LFS about a sustainably harvest or aquacultured specimen from Quality Marine today!