FIRST RECORD OF THREE HOSTS INFECTED BY THE PLEROCERCOID OF OTOBOTHRIUM PENETRANS LINTON , 1907 ( CESTODA : TRYPANORHYNCHA ) IN KHOR UMMIA , ARABIAN GULF

Three different stages in the development of the plerocercoid larvae of the trypanorhynch cestode Otobothrium penetrans Linton, 1907(two plerocerci and one post larva) were described from the various sites of needlefishes. First and second stages of plerocercoid found in the muscle, body cavity, gas bladder, kidney and some time in the heart of the yellow spot tail needlefish Strongylura strongylura, banded needlefish Strongylura leiura hound needlefish, Tylosurus crocodilus and flat needlefish Ablennes hians, while the post larva found only in intestine of S. leiura. All needlefishes except T. crocodilus consider new hosts record to Otobothrium penetrans in the world. No monthly pattern was observed either in prevalence of infection or mean of intensity except clear peak in mean intensity of infection in S. leiura during July (77) and T. crocodilus during October (75). Both the prevalence of infection and mean of intensity were increased from smallest fish length less than 200 mm until 500 mm and then the infection was decreased in the largest fish length more than 500 mm of S. strongylura.


Introduction
Trypanorhynch cestodes mature in elasmobranchs and often use teleost fishes as intermediate or transport hosts (21).Most studies in Arabian Gulf were out of Iraqi water and pointed on survey of the marine cestodes in fishes (20; 27; 11; 12; 25; 13; 8; 4; 5; 9; 10).Only three different studies dealt with parasitic tapeworms of marine fishes in Iraqi water (2; 3; 6).Because there were no studies have been done on ecological and biological aspects of trypanorhynch cestodes in Iraq, this study come to through a light on the developmental stages of plerocerci that infect four species of the needlefishes and some ecological aspects of this parasite.As soon as were captured the specimens were frozen.In the laboratory the fishes were thawed from ice, dissected then examined for the presence of parasites in the body cavity, viscera and filet the flesh for revealed encysted larvae.Cysts dissected out in saline till larvae excysted.The specimens were washed and shaked vigorously with tap water, they were pressed gently between two slides and fixed in 70% ethanol, stained with semichon'carmine, dehydrate in graded series of ethanol, cleared in toluene and mounted in Canada balsam.For Parasites identification followed ( 28) and ( 23).For Ecological terms followed (17).All measurements are given in milimetre.

Development of plerocerci of O. penetrans in needlefishes
Three different developmental stages of plerocercoid cestode O. penetrans Linton, 1907 were described from four belonid fish species including two stages of plerocerci and one post larva (table, 1).1-The first stage of plerocercoid of O. penetrans (Fig. 1A) High numbers of blastocysts were removed from musculature, body cavity, gas bladder, kidney and some time from the heart of all four belonid fishes, although more than half of plercercoid were found between dorsal spines of vertebral column.The larva (based on 20 specimens) found in white or milky cyst (blastocyst), have different shapes according to site of infection.The cyst were spindle, spherical, oval to elongate slender 2.44-5.08(3.12)x0.45-0.61(0.51), the median part of the scolex exhibit elongate and slender and followed by a swollen pars bulbosa with laterally recurved bulbs (fig.1A).Length of the scolex 2.42-2.93(2.61), pars bothridialis 0.215-0.252(0.224),pars vaginalis larger than both pars bothridialis and Pars bulbosa, pars vaginalis 1.104-1.289(1.148),pars bulbosa 0.287-0.337(0.309)contains of two pairs of oval bulbs overlap 0.23-0.318(0.26) x 0.115-0.166(0.13).Pars No monthly changes was observed either in prevalence of infection or mean of intensity during collection period except clear peak in mean intensity of infection has been found (77) in S. strongylura during July and (75) in T. crocodilus during October (table 2).

Variations in infections with length of S. Strongylura
Both prevalence of infection and mean of intensity of O. penetrans were increased with advancing in fish length until the largest length category that the infection was decreased (table 3).Discussion (14) described O. penetrans as a new species from the flesh of Tylosurus acus in the Bermudas.Later Linton (15) were recorded some plerocercoid from the flesh of another belonid T. raphidoma (23).( 23) reported and redescribed this cestode from flesh of four belonids including three full-beak needlefish T. acus, T. crocodilus and Platybelone sp. and one half beak needlefish Hyporhamphus dussumieri in Philippine waters.O. disacum and Otobothrium sp. were recorded from Arabian Gulf.They were found in body cavitities of Nemipterus japonicus and Mullidfish Parupeneus cyclostomus (9).The first and second stages in the development of plerocercoid of O. penetrans in this work similar to that from Philippine water; moreover they closely resemble specimens from Platybelone sp.(23).In this study some variability in scolex measurement were noticed that ordered it as two stages of development similar to that of four developmental stages in plerocercoid of Gilquinia squali in eyes of whiting which reported by (16).The variability in scolex measurement might be due to several reasons such as the age of the plerocercoid or storage and fixation (23) or population density and infrapopulation differences (7).This variability were neglected by (26) when gave a brief data on 15 species within genus Otobothrium and described of O. kurisi Shield, 1985, but (23) confirmed the last species was synonymised with O. penetrans, and noted a high scolex variability within the species.
(23) and ( 24) found plerocercoid in flesh and body cavity of widely variation in scolex measurement, (22)  probable more than ten years (17).Slightly variation in prevalence of infection among four belonids belong to changing in their diet, feeding habitat or migration of some species such as S. strongylura from marine to brackish waters leaded to dissimilarity in food composition, fish length and need to bigger prey(3).Generally both prevalence and mean intensity of infection by O. penetrans was high in Khor Al-Ummia in comparison to Philippine and Indonesian waters, maximum intensity was 75 in compared with 8 and 2 respectively from T. crocodilus.(23; 22).Moreover S. leiura was the perfect host to O. penetrans to harbour higher prevalence and mean of intensity (24).The infection of S. strongylura with O. penetrans were increased with advancing of fish length until the fourth length category that reached to higher value, since to increased of food intake including infected intermediate hosts with advanced of fish length or continuous accumulation of worms with age progress that unable to exist from fish body(3).The infection was decreased in largest fish probably because of changing of diet, death of heavy infected fish and development of host's immunity (18).
A total of 230 fish 30-570 cm in length belong to four species of Belonidae were collected from Fao near Khor Al-Ummia north-west Arabian Gulf (

Table ( 3): The changes in prevalence and mean intensity of infection by O. penetrans with different length categories of S. strongylura
obtained specimens of plerocercoid from Indonesian coasts had larger scolex sized about twice as larger than that from Philippine water.However having similar scolex proportion and scolex ratio and he considered O. pephrikos Dollfus, 1969 as a junior synonym of O. penetrans.The occurrence of plerocerci of O. penetrans in all four belonids except of T. crocodilus in this study considered new host record and three belonid fishes were added as second intermediate hosts.The Infection of four belonid fish with plerocerci of O. penetrans guide to the similarity of intermediate hosts structure in their diet (24; 1).No seasonal variations in infection with parasite was noticed, caused by availability of infected intermediate host in most time of year or to prolonged of plerocercoid life span that may be as long of host age, that