Feeding of Larval Lamprey

Abstract

The feeding mucus in larval lamprey is produced by the lateral walls of the pharynx and by glandular goblet cells on gill filaments. The mucous complex has 14 lateral branches which move inward to the middle of the pharynx, where they are collected and directed back to the esophagus. Mucus, which is carried by intrapharyngeal ciliary tracts and water currents, fills virtually every space in the pharynx, resulting in high (75%) entrapment efficiency. Based on indirect calculations, algae accounted for only 0.14–1.5% of the gut contents in larvae of European brook lamprey (Lampetra planeri). Although the bacterial film associated with algae, detritus, and sand grains may be an energy source for ammocoetes, suspended bacteria cannot support growth in laboratory experiments. Selective feeding on different species of algae is common among lampreys and is based on three factors: (1) susceptibility to capture in the feeding–respiratory flow differs among particles, (2) filtration of long filaments by the oral cirri, and (3) selective agglutination at the mucous filter. Fragilaria, Cocconeis, and Oscillatoria species are present in relatively low numbers in the gut whereas Navicula species are ingested with greater frequency than they occur in the environment. The size distribution of ingested particles is, in general, independent of the size of the ammocoete. Feeding rate depends on temperature and to a lesser extent, food density. In the laboratory, ammocoetes digest and assimilate only 30–40% of the protein, lipid, and carbohydrate (excluding cellulose) and 6–7% of the cellulose in their food. Therefore, larvae of many species pass large quantities of undigested algae and other food through their guts, particularly at low temperatures.Key words: algae, ammocoetes, assimilation efficiency, bacteria, detritus, feeding, lamprey, mucous complex