Plainfin Midshipman, Porichtys notatus
Plainfin Midshipman, Porichtys notatus. Fish caught from coastal waters off Santa Cruz, California, September 2023. Length: 27 cm (11 inches). Catch, photograph and Identification courtesy of Vince Golder, Santa Cruz, California.
The Plainfin Midshipman, Porichtys notatus, is a member of the Toadfish or Batrachoididae Family, and is known in Mexico as pez-fraile de aleta lucia. The “midshipman” name comes from the line of photophores found on their body that are positioned similarly to the uniforms of midshipmen — the lowest-ranking naval officer of any navy. The Plainfin Midshipman is known for its “singing” abilities. During breeding, both male and female fish will vocalize to attract mates. The sound is well known among houseboat residents and has earned the fish nicknames of the “California singing fish,” or the “Humming Toadfish,” as well as becoming the namesake for The Sausalito Humming Toadfish Festival. Globally, there are fourteen species in the genus Porichthys, seven of which are found in Mexican waters, one in the Atlantic and six in the Pacific Ocean.
The Plainfin Midshipman has an elongated body that is an olive brown color with a dark iridescent purple dorsal surface that transitions to golden yellow ventrally. They have a large slightly flattened head with eyes on top, canine teeth, and a prominent non-venomous spine on their gill cover. The anal fin has a dusky margin and the dorsal fin is either plain or has a dark margin. There are four lateral lines of ov er 700 photophores on the head and sides of the body.
A few adults have 6 or 7 saddles. The juveniles have a weak dorsal saddle. They have a white space under the eye and a black crescent below. The posterior margin of the mouth is white. The anal fin has 30 to 35 anal rays; the caudal fin is rounded and narrow and is not joined to the anal and dorsal fins; the first dorsal fin has 2 spines; the second dorsal fin has 33 to 38 rays with a long base, and the pectoral fins are broad with 16 to 20 rays. The Plainfin Midshipman is both sexually dimorphic and dimorphic between the two males. Females can range from 9.6 – 15.2 cm in standard length and can weigh 11.1 – 47.3 g. Type I males measure 12.0 cm – 21.0 cm in standard length and can weigh 30 – 206 g. Type II males weigh 3.9 – 17.3g, and measure 6.5 – 10.5 cm in standard length. They have 9 to 12 lower gill rakers. They do not have scales, and the skin is smooth to the touch.
The Plainfin Midshipman is a demersal species that is found during the non-breeding season over sandy and muddy bottoms at depths up to 383 m (1,255 feet). They are one of the largest toadfish reaching 38 cm (15 inches) in length. Juveniles feed on small crustacean larvae and zooplankton. Adults make vertical migrations at night to feed at nighttime preying on crustaceans and fish. In turn they are preyed upon by shore birds, crustaceans, fish mink, otters, seals, and sea lions. They are known to host the parasitic copepods Hamaticolax prolixus and Lepeophtheirus remiopsis. Reproduction is oviparious and occurs in the late spring with migrations from the depths to the rocky intertidal zone. The males are dimorphic designated as Type I and Type II. Type I out number Type II males by 9 to 1. The Type I male claims a nest site in the intertidal zone and prepares a cavity under rocks or boulders and then courts females via the use of its photophores. Both sexes produce sound utilizing the muscles of its modified swim bladder. When many breeding males are present the underwater courtship calls can be heard on land. The female deposits 200 to 400 eggs in the cavity, which attach to the cavity wall are then fertilized by the male. Once the female spawns, she leaves the eggs in the care of the male and departs. The males then attracts additional females and the nest can end up with over 1,000 eggs. The male tends the larvae until they reach their juvenile stage and leave the nest, about 45 days after fertilization. The Type II male is much smaller than Type I. They do not build nests but are known to enter the nests and fertilize the eggs. The males can become stranded as the tide recedes, even becoming beached completely out of the water. They survive by having the ability to breathe air.
The Plainfin Midshipman is distinguished from other midshipmen by the positioning of its photophores and by its unmarked fins. In the Plainfin Midshipman the branchiostegal photophore series is V-shaped.
The Plainfin Midshipman is a resident of Mexican waters of the Pacific Ocean but have a limited range being found from Magdalena Bay north along the central and northwest coasts of the Baja Peninsula.
From a conservation perspective the Plainfin Midshipman is currently considered to be of Least Concern with stable, widely distributed populations. They are small in stature, seldom seen by humans. From a scientific perspective the Plainfin Midshipmen has been extensively studied due to the sound production abilities during reproduction events and specializations of its swim bladder.