Nutrition of the hake (Merluccius merluccius), bogue (Boops boops), striped mullet (Mullus barbatus) and pandora (Pagellus erythrinus) in the Bay of Kaštela

Abstract

       Research about the nutrition of 363 specimens of Hake, 79 of Bogue, 282 of Striped mullets and 259 species of Pandora, has been carried on the bisis of the trawler catches which were realised during 1963/64 year in the bay of Kaštela.

       Examinations were performed in relation to the qualitative and quanti­tative composition of the food, seasonal changes of food, as well as the influ­ence of the temperature to the change of food quantity in the stomach.

       By the qualitative analysis of the food structure it was optenly possible to determine the organisms up to the genus or species. In order to find out the quantity of food in the stomach we used the degree of stomach fullness according to which: A = empty stomach, B = very little amount of food, C = half of the stomach filled with food, D = completely stomachfull with food, E = the wall of stomach thin owing to the abundance of food.

       The material for the examination was immediately preserved in 10% formalin on the vessel and few days later the qualitative-quantitative ana­lysis was performed in the laboratory. By the qualitative analysis of the Hake’s food in the bay of Kaštela it has been found that this kind of fish feeds by fish (56,1%), by crabs (6,3%), and cephalopods (0,5%). The kind of fish es such as: Sardine pilchardus and Engraulis encrasicholus form elementary, main food. The other species of fish such as: Cepola rubescens, Maena maena, Maena smaris and Diplodus annularis appear in the nutrition of the hake in the course of the year with individual species. As far as crabs are concerned only two groups of crabs were found out: Processa canaliculata and small specimen of Homarus gammarus Cephalopods were represented with the spe­cies of: Alloteuthis media and Loligo vulgaris. Registered species of Ophiuroidea (Ophiura texturata) and Thallophyta (Vidalia volubilis) probably after­wards came to the stomach from the trawler. From the qualitative analysis of the food found in the Bogue it has been found out that the great majority of the identified organisms belong to the zooplankton i.e. to the groups of copepods and copelats. It has been distingushed 22 kinds of Copepods, among which the most frequent were the following: Temora stylifera, Centropages typicus, Centropages kröyeri, Candacia armata, Isias calvipes. Among the copelatas the most numerous were the following: Oicopleura longicauda and Oicopleura dioica. The other registered groups were: Decapoda larvae, Chaetognatha, Ostracoda, Isopoda, Mysida, Amphipoda, Nemertina, Pteropoda, Pisces, the parts of Spermatophyta and Thallophyta were found in the con­siderably low number.

       The qualitative analysis of the Striped mullet’s food it has been found three groups which form 74,1% of its food Polychaeta (40,8%), Lamellibranchiata (19,4%) and Crustacea (13,9%). From polychaeta the most dominating were the following species: Sternaspis scutata, Lumbriconereis, gracilis, Nephthys hystricis. Lamellibranchiata with the species: Tellina nitidi, Leda fragilis, Cardium aculeatum and Crustacea: Processa canaliculata.

       The other registered groups are: Gammarida, Mysida, Isopoda, Copepoda, Ophiuroida, Coleoptera, Nemertina, Gastropoda, Cephalopoda, Thallophyta and juvenile Pisces have been found in a smaller quantity.

       By qualitative analysis of the Pandora’s food it has been found out that 68,4% of the whole nutrition from the groups of Polychaeta, Lamellibranchiata and Crustacea. P o l y c h a e t a  (24,6%) with dominating sorts: Sternaspis scutata, Lumbriconereis impatiens, Glycera rouxi and Nephthys hystricis. L a m e l l i b r a n c h i a t a  (23,7%) with the sorts: Tellina nitida, Leda fragilis and Cardium aculeatum. C r u s t a c e a  (20,1%) with the species: Processa cana­liculata, Portunus corrugatus, Eupaguridae sp. The data about the seasonal changes of the food in the Hake show that fish dominate during the whole year, and with clearly expressed walues in autumn and winter period when echosounder recorded large quontity of pelagic fish. In those monthes: De­cember January and February the Hakes stomachs were filled with anchovy and sardine. In the spring period the stomachs were filled mostly with sar­dine. Nutrition of fish in the summer period rapidly dropped and large amount of specimens were with completely empty stomachs. The group of Crustacea we meet almost during the whole year, but with some larger amount in autumn and spring period. The seasonal changes of Bogue’s nutrition show that dominant zooplankton group of copepods has two singnificant maxi­mums. One larger in autumn period and the other lower in the spring period. During winter period the group of copelats form the elimentery amount of the Bogue nutrition.

       The results of seasonal changes in the nutrition structure of the Striped mullet shows the group of Polychaeta form the elementery amount of the food during the whole year, but with some higher walues in spring and sum­mer period. Lamellibranchiata have one significant maximum in autumn period while Crustacea show the highest walues during the vinter monthes.

       The seasonal changes of the Pandora’s food composition do not show explicit differencies during the year in the qualitative relationships between to groups of Polychaeta, Lamelibranchiata and Crustacea, as it is case with the Striped mullet. Higher values of Polychaeta are obtained in the spring and summer period, Lamelibranchiata in winter and Crustacea in the spring and summer monthes. The minimum walues of Lamellibranchiata and Crustacea are noted during the winter monthes, and Polychaeta in the spring. The quan­titative relationships between the gropus and species were obtained on the ground of the distinguished number ou specimens. By following the monthly changes of food quantity in the stomachs and the temperature of bottom water positive relationships were obtained in Bogue, Stripred mullet and Pan­dora i. e. by increased bottom sea layer temperature during autumn and spring-summer period, the higher values of stomachs fullness were obtained. In the all three mentioned groups during winter monthes by lower tempe­ratures, the lower nutrition intensity was noted. The similar regularity we could not find with Hake since in these species the maximum values of nutri­tion intensity were noticed just during winter monthes, when the sea tem­perature was the lowest (11,9°C).

       Opposite to it during the summer monthes by te increased sea tempe­rature (from 15°C up to 24°C) the amount of food in the stomach rapidly drops.

       On the ground of our observations about the changes of the quantity of food and the sea temperature during the year, for the different to Bogue, Striped mullet and Pandora, the temperature in the registered limits does not have stronger influence to the Hake’s nutrition intensity, but it seems to us that the quantity and availability especialy of pelagic fishes (sardine, anchovy) in our case determine the Hake’s nutrition intensity.