Bighead Sand Perch, Diplectrum euryplectrum

Bighead Sand Perch, Diplectrum eurylpectrum. Fish caught from coastal waters off  Point Palmilla, Baja California Sur, April 2018. Length: 13 cm (5.1 inches).

Bighead Sand Perch, Diplectrum euryplectrum: preoperculum.

Bighead Sand Perch, Diplectrum euryplectrum: preoperculum. Fish caught from coastal waters off Mazatlán, Sinaloa, October 2019. Length: 17 cm (6.5 inches). Photograph courtesy of George Brinkman, Guelph, Ontario, Canada.

The Bighead Sand Perch, Diplectrum euryplectrum, is a member of the Sea Bass or Serranidae Family, and is known in Mexico as serrano extranjero. Globally, there are twelve species in the genus Diplectrum, of which ten are found in Mexican waters, two in the Atlantic and eight in the Pacific Ocean.

The Bighead Sand Perch has an elongated body with an overall grey-brown coloration and white belly. It received its common name from its large (43% of standard length) head. They have  a series of characteristic markings including four double dark bars on the sides, two horizontal rows of gold speckles, a large dark spot on the base of the tail, a series of yellow stripes on the head and a purple spot on the gill covers. The anal fin is transparent with a very wide yellow-brown stripe, the caudal fin has 2 very wide yellow-brown stripes and the dorsal fin is grey with a continuous yellow-brown stripe running its length. A key to identification is a dark line at the bottom of the rayous portion of the dorsal fin (as pictured below). They have dusky pectoral and pelvic fins. The head has a wide, squarish bony cheek spur (preoperculum) with 6 to 12 large spines (as pictured above), whose shape is a key to identification.

The Bighead Sand Perch is found over sandy bottoms at depths between 15 m (50 feet) and 121 m (400 feet). They reach a maximum of 21 cm (8.3 inches) in length, established by a fish that I caught. The Bighead Sand Perch are synchronously hermaphroditic possessing both males and female organs and capable of producing eggs and sperm at the same time. They spawn in deep water as mating pairs. Their eggs and larvae are pelagic and move to shallower waters as they mature. The Bighead Sand Perch 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 Bighead Sand Perch is a resident of Mexican waters of the Pacific but has a limited distribution being found from Magdalena Bay, Baja California Sur, southward along the southwest coast of the Baja, in the lower third of the Sea of Cortez, and along the coast of the mainland south to Guatemala.

The Bighead Sand Perch is difficult to correctly identify as there are eight very similar looking Sand Perches, all of the Diplectrum Genus, that reside in Mexican waters of the Pacific Ocean. The key to a correct identification is the unique shape of the preoperculum. See Sand Perch Preoperculum for an interesting side-by-side look at some fish anatomy of seven very similar looking fishes of the Diplectrum Genus found in the Pacific Ocean.

From a conservation perspective the Bighead Sand Perch is currently considered to be of Least Concern with stable widely distributed populations. They are too small to be of interest to most. They are fairly abundant in the greater Los Cabos area of Baja California Sur and efforts at “catch and release” normally do not go well as they will not return to the deep and float on the surface and are almost immediately consumed by the ever vigilant Magnificent Frigate, Fregata magnificus, who post consumption, will always return to the ocean for drinks of water, providing for splendid entertainment.