Dwarf Perch, Micrometrus minimus
The Dwarf Perch, Micrometrus minimus, whose common Spanish name is mojarra enana, is a member of the Surfperch or Embiotocidae Family, known collectively as mojarras viviparas in Mexico. There are only two global members in the genus Micrometrus, both found in Mexican waters of the Pacific.
The Dwarf Perch have highly compressed deep oval bodies with a depth that is 43 to 47% of standard length. They are silvery with black edged scales, random blotches on their sides, and a series of faint stripes on their sides behind their pectoral fins. They have a large black blotch at the base of their pectoral fins and a dark line just below their dorsal fin commencing at the fourth dorsal spine. Their head has a concave upper profile with large eyes and an oblique mouth. Their anal fin has three spines; their caudal fin is forked; and their dorsal fin is singular and continuous with seven to nine spines and 19 to 28 soft rays. Their lateral line is noticeable and their body is covered with disproportionately large scales.
The Dwarf Perch are typical bottom dwelling inhabitants of inshore exposed rocky reefs including rocky tidal pools, eelgrass (Zostera) in bays, and around jetties at depths up to 30 feet. Females reach a maximum length of 16.0 cm (6.3 inches) and males are only about half this length. The Dwarf Perch are of significant scientific interest because they are only one of two global fish having males born sexually mature, i.e. ready to rumble. Females reach sexual maturity in one year and significantly outnumber males, except at birth, indicating that males die off soon after birth. They express strong sexual dimorphism with males being smaller than females and slower growing. Males live about half as long as females (one year versus two to three years). Males are also unique among all spiny rayed fish in that they have more anal fin rays than females. They prefer water temperatures between 11oC (52oF) and 21oC (70oF); if water temperatures exceed 23oC (74oF) they will escape to cooler deeper waters. Juveniles feed on small crustaceans, amphipods, polychaetes, and mollusks. As they mature, their diet changes to partially herbivore and then to omnivore. Reproduction is viviparous with mating occurring in the summer. Gestation lasts six months with each female producing 2 to 50 fry annually that are 2.5 cm (1.0 inch) to 3.5 cm (1.4 inches) in length; larger females produce larger quantities of fry.
In Mexican waters the Dwarf Perch have a limited distribution being found only from Cedros Island northward along the central and northwest coasts of Baja.
The Dwarf Perch is straightforward to identify due to its body profile and coloration and is therefore not easily confused with any other species.
The Dwarf Perch are exceedingly small in stature and have no commercial or economic value. They are normally a “catch and release”, however, are retained by subsistence fishermen. They are a favorite of beginning anglers and are a minor component of the pier fishery. They are also used as live bait on a limited as-available basis.