Ammodytoides xanthops – Yellow face sandlance

Ammodytoides xanthops – Yellow face sandlance ©FAO/M. Lipperi

The Yellow face sandlance is a relatively small fish found in the sandy areas off Mozambique. It is characterized by an elongate and slender body with black spots tracing the edge of the dorsal fin, and bright yellow head.

The discovery

This species was discovered on 16 October 2007 by P.C. Heemstra and E. Heemstra, during an expedition aboard the research vessel Dr. Fridtjof Nansen in the western Indian Ocean. While conducting a survey off the coast of Mozambique, they collected 18 specimens of an Ammodytoides species in a single trawl at a depth of 26–28 m during the early morning. These specimens included both ripe males and females, which explained their presence in the net. Typically, members of this family evade capture by staying close to the seabed, burrowing, or using their speed to escape. However, during spawning they tend to swim higher in the water column, making them more susceptible to trawl nets. On 19 October an additional specimen was collected at a depth of 62 m, further contributing to the understanding of this species.

Features and characteristics

The yellow face sandlance displays a distinctive combination of features, such as a dorsal fin which has 48 or 49 rays, a lateral line marked by 106 to 112 scales, and an opercle that lacks small scales on its upper surface. When freshly caught, the species is visually striking: its dorsal side is dark purplish-grey, fading into a pale silvery-blue along the sides and ventral surface. The region between the eyes and most of the head is bright yellow, while the snout’s front and the tip of the lower jaw are shaded dusky. A line of six or seven black spots traces the edge of the dorsal fin, but none are found on the other fins. The caudal fin is distinguished by a broad blackish border along its posterior edge.

This species is a member of the Ammodytidae family, commonly referred to as sandlances. Often called sand eels – despite not being true eels – these intriguing small fish hold a vital role in marine ecosystems. Their streamlined bodies make them excellent burrowers in sandy seabeds, a skill they use to hide from predators and to rest. These small fish also form shimmering schools, which offer them safety in numbers and are a mesmerizing sight underwater. Without a swim bladder, they stick close to the seabed or burrow into the sand, and some even hibernate in deeper layers during colder months.

They feed on zooplankton and exhibit adaptations such as a protrusible jaw, a relatively short snout for precise binocular vision, reduced or absent teeth, and long gill rakers. Their streamlined elongated body, protective adipose eyelid, forked caudal fin, and low dorsal and anal fins which fit neatly into grooves, are specialized for swift swimming. Positioned near the centre of their head, their eyes provide a wide field of vision, allowing them to detect predators both above and below. If escape is necessary, they dive into the sand, aided by their pointed, projecting lower jaw and the ability to fold their fins into grooves.

Ammodytes tobianus (retracted and protruded jaw). ©FAO

A specimen of Ammodytoides xanthops from the R/V Dr. Fridtjof Nansen 2025 Mozambique survey. ©FAO/K. Bemis

The protrusible jaw of sandlances is a remarkable adaptation that enhances their feeding efficiency. This flexible jaw structure allows them to extend their mouth outward to capture prey such as plankton and small invertebrates with precision. The mechanism provides a rapid, efficient way to snatch food while minimizing energy expenditure, making it particularly advantageous in their dynamic sandy habitats.

Geographical distribution

Mozambique.