Reproductive biology and feeding ecology of gurnards

• Main Author: Gökce, M. A.
• Published: Swansea University 1998
• Subjects: 591.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637060

Tub (<I>Trigla lucerna</I>), Red (<I>Aspitrigla cuculus</I>) and Grey (<I>Eutrigla gurnardus</I>) gurnards exhibit a distinct reproductive cycle. The spawning periods of Tub, Red and Grey gurnard occur from March to July, February to August and February to July respectively. The spawning periods of all three species commence at a minimum sea temperature (approximately 8°C) with the onset of increasing daylength and cease with the onset of decreasing daylength. A highly significant correlation was found between absolute fecundity and total weight of all three species. The relative fecundities of the three species are similar, 234-414 per g body weight for Tub, 271-377 per g body weight for Red and 306-551 per g body weight for Grey gurnard. The ovaries of Tub, Red and Grey gurnard can be characterised as asynchronous ovaries. Histological and ultrastructural studies reveal that these three species have similar oocyte development patterns. There was no hiatus or gap observed in the recruitment of oocytes from the PGP into the SGP or between the different oocyte developmental stages. Two types of yolk inclusions are formed: Lipid vesicles which appear in the mid and outer cortex indicate the initiation of the SGP and later migrate to the inner cortex and coalesce into a single lipid mass and protein yolk granules which initially form as small granules in the outer cortex of the cytoplasm. On maturation they fuse into large granules packing the cortical cytoplasm. In all three species Crustaceans and Teleosts are the preferred prey. Red gurnard had the broadest diet, Grey gurnard had the narrowest. The lowest diet overlap was observed between Grey and Red and the highest between Grey and Tub gurnards. This considerable diet overlap occurring between Grey and Tub gurnard may lead to interspecific competition for food.