Morphological characters of fish larvae¾ as well as their ecological niche¾ may change dramatically in the course of larval development, i.e., the period from hatching to metamorphosis. This is true for body proportions as well as for pigmentation. Spines, teeth and fin rays begin to develop around the mid-time of larval development. Such variability makes fish larvae difficult to identify.

Froese (1990) developed and compared different computer-based methods for identification of fish larvae, including numerical taxonomy, expert systems and relational databases. He concluded that overall, the database approach was the easiest to implement and use, because most larvae could be identified by a combination of few characters only (see also Froese 1988, 1989; Froese et al. 1989, 1990; Froese and Papasissi 1990).

To date, the LARVAE table covers over 1,000 species mainly from the North Atlantic and the Mediterranean. Relevant information has been derived from more than 800 references such as d’Ancona (1956), Russell (1976), Fahay (1983), Moser et al. (1984) and Halbeisen (1988).

For postlarvae (i.e., larvae in a development stage between absorption of yolk-sac and metamorphosis) the table provides fields for the Length at first feeding, the Months when the larvae occur, the typical water parameters such as ranges of Depth, Temperature, Salinity and Oxygen concentration.

Because of their variability, many of the following descriptive, meristic and morphometric characters are given as a range from ‘early’ to ‘late’ stages.

For descriptive characters, the table accommodates Striking features such as ‘stalked eyes’ or ‘tube-like snout’, and Striking shape such as ‘eel-like’ or ‘tadpole-like’. Since such features are rare, they drastically reduce, when they occur, the number of species that need to be considered in an identification session.

The Shape of gut is also a distinctive character, and may be triangular, spherical or looped, elongated, tube-like or aberrant. The Gas bladder may be visible, invisible or pigmented. Spinal armature may be present at different locations on the head.

Rows of melanophores may be present on the tail as: dorsal row; ventral row; lateral row; dorsal + ventral row; dorsal + lateral row; ventral + lateral row; dorsal + lateral + ventral row; no rows. It has been shown that these pigmentation patterns are very powerful characters for identifying fish larvae (Halbeisen 1988; Froese 1990). Other melanophore patterns may be present on the tail, head and trunk and are classified in two additional choice fields.

Urostyle region and Peritoneum may be pigmented; Pectorals and Pelvics may be absent or of striking shape, with or without melanophores.

Meristic characters pertain to the number of Myomeres or Vertebrae, counted in total and/or from head to anus. Additional characters of postlarvae are given in a text field.

Finally, the LARVAE table contains fields for metric characters in percentage of a Reference length, i.e., Preanal length, Prepectoral length, Preorbital length, Diameter of eye, Depth at eye, Depth at pectorals, and Depth at anus, for early, flexion and late postlarval stages.

For yolk-sac larvae, the table first describes the typical Larval area in a text field. It then gives the Place of development, the Length at birth, the Preanal length (i.e., from snout to anus) as percent of total length, the shape and pigmentation of the Yolk-sac, the consistency of the Yolk, and the number, position and pigmentation of Oil globules in the yolk.

The pigmentation of the yolk-sac larvae on head, trunk and tail is classified into the most common patterns and is a main entry for identification. Additional characters are presented in a comment field.

You get to the LARVAE table by clicking on the Biology button in the SPECIES window, the Reproduction button in the BIOLOGY window and the Larvae button in the next window.

I acknowledge the contribution of the late Hans-Wilhelm Halbeisen who showed that the pigmentation patterns in fish larvae can be classified. He developed¾ based on this discovery¾ the first concise fish larvae identification key for a larger area. Many of the larval pictures in FishBase are based on illustrations in his key (Halbeisen 1988). I also thank Wolfgang Welsch for his help with digitizing many of the larvae pictures. Finally, I thank Christine Papasissi for performing many of the measurements in the morphometrics section of the LARVAE table.