Controlling methods investigation of the Caspian Sea invasive Ctenophora ( Mnemiopsis leidyi)
The presentation of ctenophore Mnemiopsis leidyi and explosive development in all Caspian sea especially in southern parts greatly affected in the ecosystem and fish stocks same as Black sea. Following the sharp decreses of kilka fish catch. Some project were developed in order to study the controlling methods of Caspian sea ctenophora. The first section of this study, the gut content of 653 specimens from 7 different species of the native Caspian sea fishes were studied during 2002 to 2004. The factors; index of vacuity gut, relative length gut, condition factor, index of fullness, frquencey and abundance of food were estimated. In second section of study, ctenophore Beroe ovata was candidate as a control agent against the invasive ctenophore Mnemiopsis leidyi. The acclimation, survival and some physiological characteristics including feeding, reproduction and growth of B. ovata were studied in Caspian Sea water (12.6 ppt salinity) conditions. The animals transported from the Black and Marmara Seas to laboratories on the Iranian Caspian coast during 2001 and 2002. The finding of the diet study on native fishes showed that Alosa caspia caspia and Clupeonella spp. feed from plankton organisms with unfavorite degree as well as they had a low diversity of preys. The dominated prey were the Acartia from copepoda and Balanus cypris from cirripedia. The Vimba vimba persa had a variety of the diet where the carnivorous were most with a medium fullness index. The Neogobius bathybius was identified benthophage with a medium variety of diet. The fishes of Alosa brashnikovi and Sander lucioperca had a favorite diet and were carnivorous on medium ecosystem levels. In totally the ctenophora Mnemiopsis leidyi were not seen in diet of fishes but it is necessary to study more about the filter feeding fishes in the field of Caspian sea and the laboratory. The findings of the study showed that when salinity was gradually decreased from 22 to 12.6 ppt, B. ovata were able to adapt well to Caspian Sea water. All sizes of the B. ovata intensively consumed all sizes of M. leidyi, however the largest M. leidyi specimens were preferred by all the different size groups of the predator cetenophore. The average daily rations of B. ovata ranged from 26 to 43 % wet weight for specimens that initial wet weight could vary between 0 to 95 % in long-term experiments. The relationship between the specific daily ration and B. ovata wet wt described with power function that is mostly depend on prey biomass and the food concentration is important on the B. ovata feeding. The average interval digestion time between 2 consumption for B. ovata was 415 ± 298 min. The digestion time averaged 99 ± 57 min for prey : predator ratio. Totally B. ovata specimens were spawned and their eggs were hatched in Caspian Sea water, but the survival was very low and the larvae survived for only a few hours. During the experiments of 2001, 138 eggs were obtained and 7 larvae were hatched but no larvae survived after 24 hours. The results of reproduction study in 2002 was same as 2001 where the results was better in black sea water for two year. This study could be known as the first step to consider the predator of B. ovata as on important bio-control agent against the M. leidyi which caused immense ecological and economical problems in the Caspian sea. There are still necessary studies (e.g. on parasites, feeding with other native organisms, modeling etc) relating to possible impact of the introducing B .ovata into Caspian sea to be done.
| Main Authors: | , , , , , , , , |
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| Format: | Report biblioteca |
| Language: | Persian |
| Published: |
Iranian Fisheries Science Research Institute
2005
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| Subjects: | Method, Ctenophora, Mnemiopsis leidyi, Investigation, |
| Online Access: | http://hdl.handle.net/1834/14414 |
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