Porichthys notatus

Porichthys notatus is a species of fish in the toadfish family. It is a midshipman known by the common name plainfin midshipman. It is native to the eastern Pacific Ocean, where its distribution extends along the coast from Sitka, Alaska, to Magdalena Bay in southern Baja California. This fish reaches up to 38 cm (15 in) in length. It is brownish to olive to iridescent purple dorsally, becoming lighter on the sides and yellowish/golden on the belly. Below the eye is a whitish patch and black crescent. A young individual may have a dark saddle-mark. P. notatus has wide pectoral fins and a narrow but rounded tail fin. Except when breeding, the typical habitats for this marine fish are sandy and muddy bottoms from shallow water just below the tide to depths of 366 m (1,200 ft). Its diet includes crustaceans and fish. It is nocturnal, feeding at night and resting during the day, when it buries itself in the sand. This fish is oviparous. The male claims a nest site, which is generally under a rock in the intertidal zone. Once the female spawns she leaves the eggs in the care of the male and departs. One female can lay about 400 eggs, but the male may mate with a few females and end up with over 1000 eggs in his nest. The eggs and larvae are adhered to the wall of the nest. The male tends them by fanning them, keeping the nest clean, and hydrating them if they begin to desiccate at low tide. He protects the larvae post-hatching until they reach their juvenile stage and leave the nest, about 45 days after fertilization. Very occasionally, an egg will yield twin larvae. The conditions of the intertidal breeding habitat change regularly with the tide. A male that tends to his nest can become stranded as the tide recedes, even becoming beached completely out of the water. The fish tolerates this well. It can breathe air. Physiologically, it is well adapted to hypoxia, as well as hypercapnia. Even its sperm are quite functional in low-oxygen conditions. These behaviors are not uniform for all males of the species. The male is dimorphic; the literature refers to Type I males and Type II males. The Type I male provides paternal care to the brood. He defends territory and courts females. The Type II male, on the other hand, does not tend a nest or court the females. He sneaks fertilizations. He is much smaller in size than the Type I. P. notatus is bioluminescent. It has photophores in the skin of its head and much of its body. One fish has over 700 photophores, each about a millimeter wide. They contain luciferin. Norepinephrine activates them, producing a distinct fluorescent green glow. The fish is only luminescent during courtship. It may however, play a role in predator avoidance, as well. In the juvenile, photophores point ventrally, directing their illumination downwards. This helps to shadow the fish in a silhouette that might make it harder for predators to see.