At least 15 kinds of fish have been found in the shallow pools and channels of the lagoon. The more common species are described below.
The California Killifish is a small olive green fish with a flattened head. It grows to 5 inches in length and may be very abundant, particularly in shallow waters. It is highly salt tolerant, resisting the high salt concentrations when the lagoon is closed off from the sea.
The California Halibut is a flatfish, having eyes either on the left or right side of the head. The upper surface of this fish is greenish brown, sometimes mottled with small white spots. This is a commercially important food and sport fish, which, in offshore waters, may reach 5 feet in length and weigh 60 pounds. Breeding occurs in coastal waters and the juveniles make their way into bays and lagoons such as Los Peñasquitos, which they use as nursery grounds.
The Bay Topsmelt has a silvery lateral stripe and a transparent greenish dorsal surface. This common and hardy fish lives in schools and may grow to a length of 8 inches.
The Mudsucker has a long, slender, slimy dull olive body with a yellowish belly. It grows to 8 inches in length, and is common but usually difficult to find since it hides in the channel banks and hibernates in the bottom mud during the winter months. This extremely hardy fish will live for a week or more out of water if kept in damp seaweed. This characteristic makes the species valuable as live bait.
The Pipefishes, like the related seahorses, are biological curiosities in that the males have a brood pouch in which the females deposit eggs and the young undergo development. They occasionally reach 8 inches in length but are rare except in Ruppia beds, where, because of their coloring and shape, they may be indistinguishable from the blades of the plant.
The Southern Staghorn Sculpin has a large head with wide set eyes and an antler like spine in front of the gill openings. This common form may grow to a length of 6 inches. When disturbed, the spine is thrown upward and outward making a formidable defensive weapon.
The Arrow Goby is slender and small (less than 2 inches in length) and is very abundant, but because it is a sand mud color, it is almost impossible to distinguish unless it is moving. This fish has the interesting habit of sharing the burrows of worms and ghost shrimps.
Next topic: Lagoon birds