Journal of Fish Biology (1995) 47, 350–353 Allopaternal care in the redlip blenny R. S. S Universidade dos Açores, Departamento de Oceanografia e Pescas, PT-9900 Horta ( A çores) , Portugal (Received 10 June 1994, Accepted 1 October 1994) Territorial male Ophioblennius atlanticus atlanticus were found to switch to experimentally deserted nests of other males and adopt their fry. This alloparental care appears to aid in acquiring additional clutches of eggs at the nest site.  1995 The Fisheries Society of the British Isles Key words: Ophioblennius atlanticus atlanticus; alloparental care; Azores. Several studies have shown the importance of eggs in a nest for increasing the probability of obtaining more eggs in fish with male parental care. Ridley & Rechten (1981) have shown that females of Gasterosteus aculeatus L. prefer to mate with males that have eggs in their nests. Jamieson & Colgan (1989) found that the presence of eggs in the nest had an effect of increasing the courting activity of the males of that species. Further evidence of an association between the presence of eggs in the nest and the probability of acquiring more mates by the males came from studies on Cottus gobio L. (Marconato & Rasotto, 1983; Marconato & Bisazza, 1986; Bisazza & Marconato, 1988), Padogobius martensi (Günther) (Bisazza et al., 1989), Pimephales promelas Rafinesque (Unger & Sargent, 1988), Etheostoma flabellare Rafinesque (Knapp & Sargent, 1989), A x oclinus carminalis (Jordan and Gilbert) (Petersen, 1989), Hypsypops rubicundus (Girard) (Sikkel, 1989), and A idablennius sphynx (Valenciennes) (Kraak & Videler, 1991; Kraak & Berghe, 1992). Bisazza et al. (1989) and Unger & Sargent (1988) reported the occurrence of allopaternal care. Advantages for the females choosing a male which already cared for eggs (Sikkel, 1989) could be related to: the reduction of losses by predation (Rohwer, 1978; Ridley & Rechten, 1981); increased paternal investment associated with accumulation of clutches (Coleman et al., 1985); and increased attractiveness of the males which show a higher capacity of caring for eggs (Ridley, 1978). If the presence of eggs constitutes an attractive trait for mating females, males must obtain eggs not only because of their intrinsic value but also because they constitute a means of obtaining more eggs, and thus of increasing their reproductive success. The present paper, reports a case where males acquire other nests from which male owners were removed experimentally; these males cared for the eggs in the adopted nest and continued to spawn with additional females. The present study was carried out with redlip blenny Ophioblennius atlanticus atlanticus (Valenciennes) a territorial inshore marine species with male parental care (Nursall, 1977). Care is given only during the embryonic stages. Larvae are planktonic, with post-metamorphic juveniles adopting a rocky benthic life, thus the probability of kin returning to the same site is extremely low. O. a. atlanticus of the Azores occurs in shallow rocky habitats from 0–15 m depth, with higher abundance from 0·5–7·5 m (Patzner et al., 1992; Patzner & Santos, 1993). The breeding season lasts through June and July and spawning occurs during the early morning. The study site was on the sea side of Horta Harbour breakwater (Island of Faial: 3831·3 N ; 2827·2 W), composed of concrete cubic blocks (2·5 m) arranged in a regular pattern from 1·5 to 10m depth. Despite their uniform shape, they possess numerous irregularities that form cavities of adequate size for the nests of breeding males of O. a. atlanticus. The site, comprising 36 blocks in three vertical rows, together with the location of the nests, was mapped. Twenty parental males were removed by hand nets 350 0022–1112/95/080350+ 04 $12.00/0  1995 The Fisheries Society of the British Isles