No abstract

Pike have been in Spain since 1949(Gutierrez-Calderon, 1954) and the first specimen in the Esla basin, in north-western Spain, was caught in 1964(Pena, 1988. Since then pike have altered the existing autochthonous fish communities in several ways.Agundez et al. (1987) reported the finding of three hermaphrodite specimens in 1986; their study was only macroscopic. The present study shows that the 18 hermaphrodite specimens caught by electrofishing between March 1986 and October 1987 in different rivers and localities in the Esla basin, comprising 094% of all pike collected, were functional hermaphrodites. Histological investigation revealed the existence of spermatogonic isles within functional ovaries.Biometric and gonad state data were taken for each specimen (Table I). Gonads were preserved in 8% formaldehyde. The gonads were cut into serial sections and stained with haematoxylin for light microscopic observation. Photographs were taken with a Nikon OPTIPHOT photomicroscope.Most of the hermaphrodites were collected in the spawning period for the species, when macroscopic detection is least troublesome. Sizes ranged between 134 and 494 mm, and all specimens were found mature for both sexes.Histological study revealed different kinds of gonad disposition: ovary and testis, ovotestis and ovary, or two ovotestes, although separation between the sexes in the gonad was not clear. TABLE I. Details of hermaphrodite pike from the R. Esla basin Date Locality Weight Length (9) (m)