original scientific paper UD C 597.5:593.16(262.3-191.2) 576.893.16(262.3) INFECTION OF SARDINE EGGS BY A PARASITIC DINOFLAGELLATE ICHTHYODINIUM CHABELARD! HOLLANDE AND CACHON, 1952 IN CROATIAN WATERS jakav DULClC Institute of Oceanography and Fisheries, HR-21000 Split, P.O. BOX 500 ABSTRACT The infection of sardine eggs by a parasitic dinofiageiiate (Ichthyoclinium chabelardi) in the eastern central Adriatic was investigated. This syndinian parasitizes the vitelline vesicle of sardine embryos and after eclosion bursts the yolk causing the death of the newly hatched larvae. Sardine eggs are mainly infected during winter period. Mean percentages of contaminated eggs were: January - 48.2%, February - 47.7%, March - 39.7%, April - 27.0%, May ­6.8%, September - 2.6%, October - 14.8%, November - 19.7% and December - 50.0%. The high mortality caused by ichthyodinium chabelardi should be taken into account in future studies of mortality during the embryonic stage. Key words; sardine eggs, parasitic dinofiageiiate, ichthyodinium chabelardi, eastern central Adriatic INTRODUCTION about the findings of this endoparasite on sardine eggs in the eastern central Adriatic. Understanding the processes affecting recruitment is a fundamental objective in fishery research. It is gener-MATERIAL AND METHODS ally assumed that the major mortality of a year brood occurs during the early life history of fishes. During the In 1990 a monthly sampling programme directed at embryonic period, abiotic factors (water temperature, hydrographic data and the plankton community was salinity, dissolved oxygen, mechanical damage, UV ra-carried out in the eastern central Adriatic by the re­diation) and predation are primary sources of mortality. search vessel "Bios". Fig. 1 shows the three locations Major causes of larval mortality seem to relate to starva-where the institute of Oceanography and Fisheries has tion and predation, and perhaps to the interaction of performed investigations for more than 40 years these factors (Hunter, 1984). (Stations KaStelanski zaljev, Pelegrin, Stondca). Diseases of fish eggs caught at sea are not well The material was collected by double vertical hauls studied, parasitism being one of the factors that can of a plankton net of "Hensen" type in the period January cause high mortality. Hollande and Cachon (1952, 1990-December 1990. Samples were fixed immediately 1953) described a new genus and species of dinofiagei-after collection in 4% buffered formalin. In the labora­iate (ichthyodinium chabelardi Hollande and Cachon, tory, plankton volumes were measured by displacement 1952) parasite of sardine eggs among the other teleost and fish eggs and larvae sorted with the aid of a stereo-eggs. In a recent review of dinofiageiiate taxonomy, scopic microscope. The formalin fixed sardine eggs Taylor (1987) considers this species as belonging to the were graded into the series of i t stages described by Subclass Syndiniophycidae, Order Syndiniales, Family Gamulin and Hure (1955). Sardine eggs contamined by Syndiniaceae. The referred endoparasite can contami-ichthyodinium chabelardi were enumerated under a nate up to 80% of Sardina pilchardus (Walbaum, 1792) stereoscopic microscope and, in certain cases, a light eggs during winter months (Meneses & Re, 1991). microscope using transmitted light. The aim of this paper is to present some new data 15 ANNALES 13/'98 fig. 1: Locations of sampling stations in the vicinity of Split, eastern middle Adriatic (A -Kaštela Bay, B - Pvlc­gr'tn, C -Stondca). SI. 1: Lokacije vzorčnih postaj v bližini Splita, vzhodni srednji Jadran (A -Kaštela, B - Pelegrin, C - Stončica). RESULTS AND DISCUSSION Sardine eggs were not found in June, July and August, since spawning period of sardine is from October (September) to April (May) (Regner et a!., 1987). Ichthyodinium chahelardi parasitizes the vitelline vesicle of sardine embryos (Fig. 2) and after eclosion the yolk sac bursts causing the death of the newly hatched larvae, in the first early stages of development of the eggs (before the c.iosure of the blastopore, stages I to V) it was not possible to detect the parasite. Thus, eggs parasitized by Ichthyodinium chahelardi (referred here­after as infected or contaminated eggs) correspond al­ways to eggs in the later stages of development (stages VI to XI). The abundance (expressed in number of eggs per 10m2) of sardine eggs sampled monthly at the three sta­tions is presented in Table 1; also presented are the abundance of infected and noninfected eggs and the percentage of contaminated eggs. Mean percentages of contaminated eggs were: January - 48.2%, February ­47.7%, March - 39.7%, April - 27.0%, May - 6.8%, September - 2.6%, October - 14.8%, November - 19.7% and December - 50.0%. From these data it can be in­ferred that S. pilchardus eggs contaminated by this synd­inian parasite occurred primarily from December to April, suggesting that infection takes place during winter months. This results are very similar to those presented Fig. 2: Sardina pilchardus eggs contaminated by Ichthy­odinium chahelardi sampled in the eastern central Adriatic (Croatian waters). Si. 2: Z zajedalskim oklepnim bičkarjem Ichthyodinium chahelardi okužene ikre sardel (Sardina pilchardus), vzorčenih v vzhodnem srednjem Jadranu, by Meneses & Re (1991) who found in Portuguese wa­ters contaminated sardine eggs primarily from January to March. Karlovac (1967) mentioned the presence of this parasite on the sardine eggs collected in the seasons 1951/52 and 1952/53 in the central Adriatic without any precise data about the occurrence, abundance, and stages of development at which parasite occur. Hol­lande and Cachon (1953) who reared infected sardine eggs in order to study Ichthyodinium chahelardi life cycle, were unable to infect other healthy eggs with the resulting spores under controlled conditions. For this reason, it is not known how and in which egg stage contamination takes place. More experimental rearing work is required to solve this and other problems related to the life cycle of this parasitic dinoflagellate. The high mortality caused by Ichthyodinium chahelardi should be taken into account in future studies of mortality during the embryonic stage, as well as in the related studies of the processes affecting recruitment in sardines and other commercial important fishes. 16 Month Station Contaminated eggs Ncmcontaminated eggs Total N of eggs Mesec Postaja (stages VI-XI) (stages VI-XI) skupno število okužene ikre neokužene ikre % N/1 Orri2 N/10m2 N/10m2 January Kaštela 47.1 27.8 27.9 78.9 Pelegrin 0.0 0.0 0.0 Stončica 49.3 17.0 119,0 331.5 February Kaštela 43.1 34.8 336.0 374.5 Pelegrin 50.0 27.9 27.9 74.4 Stončica 50.0 5.6 5.6 100.8 March Kaštela 42.9 16.6 22.1 127.0 Pelegrin 0.0 0.0 0.0 Stončica 36.4 9.2 16.1 27.6 April Kaštela 33.3 29.8 59.6 304.0 Pelegrin 1.2 6.8 544.0 587.3 Stončica 46.5 596.8 686.0 1363.0 May Kaštela 8.2 15.0 182.5 597.5 Pelegrin 0.0 0.0 0.0 Stončica 5.3 5.8 27.6 33.8 September Kaštela 3.5 4.5 12.1 27.6 Pelegrin 0.0 0.0 0.0 Stončica t.7 4.5 22.1 127.0 October Kaštela 12.8 27.9 27.9 74.4 Pelegrin 0.0 0.0 0.0 Stončica 16.7 6.2 31.0 148.8 November Kaštela 25.0 5.7 17.1 176.7 Pelegrin 0.0 0.0 9.0 9.0 Stončica 14.3 4.7 28.3 788.2 December Kaštela 50.0 27.8 27.8 331.5 Pelegrin 0.0 0.0 0.0 Stončica 50.0 5.6 5.6 100.8 Tab. 1: The abundance (expressed in number of eggs per 10 m2) of sardine eggs sampled monthly at the three stations in the eastern central Adriatic. Tab. 1; Abundanca iker sardele (izražena v št. iker na 10 m-) v mesečnih intervalih na treh postajah v vodah vzhodnega srednjega Jadrana. IKR E SARDE L V HRVAŠKI H VODA H OKUŽEN E Z ZAJEDALSKI M OKLEPNI M BiČKARjE M ICHTHYODINIUM CHABELARDIHOLLANDE I N CACHON , 195 2 Jakov DULČIČ Institut za oceanografiju i ribarstvo, HR-21000 Split, P.P. 500 POVZETEK Avtor članka poroča o raziskovanju okuženosti iker sardel, ki jo v vodah vzhodnega srednjega Jadrana povzroča zajedalski oklepni bičkar. Potem ko ta zajedalec okuži rumenjakov mešiček sardelinih zarodkov, se razpoči rvmen­ja kova vrečka in na novo odložene ikre poginejo. Oklepni bičkar okužuje ikre sardel predvsem v zimskem času. Srednje odstotne vrednosti okuženih iker so bile: januar - 48,2%, februar - 47,7%, marec - 39,7%, april -27,0%, maj - 6,8%, september -2,6%, oktober - 14,8%, november - 19,7% in december - 50,0%. To visoko smrtnost, ki jo povzroča ichthyodinium chabelardi, bi bilo po avtorjevem mnenju treba upoštevati v prihodnjih raziskavah smrt­nosti v zarodni fazi sardel. Ključne besede: ikre sardel, zajedalski oklepni bičkar, Ichthyodinium chabelardi, vzhodni srednji Jadran 17 ANNALE S 13/'98 LITERATURE Gamulin, T. & J. Hure, 1955. Contribution a la connais­sance de l'écologie de la sardine (Sardina pilchardus Walb.) dans l'Adriatique. Acta Adriat., 7 (8): 1-22. Hollande, A. & J. Cachon, 1952. Un parasite des oeufs de sardine: l'Ichthyodinium chabelardi, nov. gen., nov. sp. (Péridinien parasite). C.R. Acad. Sci. Paris, T. 235: 976-977. Hollande, A. & J. Cachon, 1953. Morphologie et évolu­tion d'un Péridinien parasite des oeufs de sardine (ichthyodinium chabelardi). Bull. Trav. Sta. Aquic. Peches Castiglione, N. S. 4: 321-331. Hunter, J. R. 1984. Inferences regarding prédation on the early iife stages of cod and other fishes. In: E. Dahe, D.S. Danilssen, E. Moksness and P. Solemdal (Eds.). The Propagation of Cod Cadus morhua L., Flodevigen Rapp. 1, pp. 533-562. Kariovac, J. 1967. Etude de l'ecologie de la sardine, Sardina pilchardus Walb., dans la phase planctonique de sa vie en Adriatique moyenne. Acta Adriat., 2: 3-109. Meneses, I. & P. Ré, 1991. infection of sardine eggs by a parasitic dinoflagellate ichthyodinium chabelardi Hol­lande and Cachon, 1952 in Portuguese waters. Bol. înst. Nac. invest. Pescas, Lisboa, 1 6: 63-72. Regner, S., F. KrSim'c, I. Marasovîc & D. Regner, 1987. Spawning of sardine, Sardina pilchardus (Walbaum, 1792), in the Adriatic under upwelling condition. Acta Adriat, 28 (1.2): 161-189, Taylor, F. R. 1987. The Biology of Dinofiagellates. Botanical Monographs, 21. Blackweell Scientific Publi­cations, London, 785 p. 18