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The ecological study of the Persian Gulf Martyres Lake carried out at the 5 stations between 2013 and 2014. This study identified 35 phytoplankton taxa. The diatoms taxa was dominated and their abundance recorded highest (2000 000 cell. l-1) in the lake. The annual phytoplankton abundance was measured as 2500 000 cell. l-1 during the study. The total nitrogen and water temperature were the significant a biotic parameters to increase cyanophytes abundance. Furthermore, 37 zooplankton taxa were identified. The Rotatoria abundance was dominated zooplankton. The annual zooplankton abundance was measured as 72 ind.l-1. Based on the CCA, there was no correlation between Rotatoria abundance and a biotic parameters. The study benthos showed Ephemeroptera and Diptera abundance were dominated; artificial bottom and lack of sediment and organic matters were the main reasons in decreasing of the benthos density. The Chitgar lake is the poorest lake in Iran due to low density of plankton and benthos organisms. The estimation of fish production was 123 kg/ha and for the lake was determaind 16 tonne. The finding display, invasive species was the main fish Chitgar lake that would be negative effect and increase eutriphication trend in the lake. Phosphorus parameter was limited parameters and trophy level recorded low due to high N/P ration in the lake. In overall the Chitgar lake situation is in Oligotrophic category with the low trophy level. Iranian Fisheries Science Research Institute Published

Phytoplankton groups are very important producers in the anzali lagoon that have a significant role in the quality of water and the need to be constantly study their sequence and density.The surveywas conducted in six workstations March 1389-Feb 2012. Samples were taken for a liter of water with plicae (P.V.C) and fixed with formalin to 4% ratio. Five ml of the sample after becoming homogeneous, was sequestration for 24 hours in the laboratory and identified and counted by invert microscope. Based on the results of this reviews 67 genus (22, 26, 9, 5, 1, 2, 1, and 1 genus respectively of the Bacillariophyta, Chlorophyta, Cyanophyta branches, Cryptophyta, Euglenophyta Chrysophyta, Pyrrophyta, the Xanthophyta) were identified. The results showed that the phytoplankton density was the most in Sorkhankol and Komeh Aghajani stations with annual average of 24387483±5643414 and 20381250 ± 5488084 per liter respectively. The Bacillariophyta ( particularly Cyclotella) was dominant in all of stations but high density of blue green algae (Cyanophyta) in Komeh aghajani station from July to mid-October have caused the annual average of these phylum is more than Bacillariophyta. In General, the average density of phytoplankton was the highest in summer than other seasons and was the lowest value in the fall. The number of the genus identified in this survay is less than previous studies. Compare this survey with the last studies reviews shows that diversity is reduced in the current situation in the anzali than previous studies. According to thestatistical analysis of the Kruskal Wallis, the density of phytoplankton had no significant differences in the different months, stations and seasons (p >0.05) but the phytoplankton phylums have significant differences (p < 0.05) together. Iranian Fisheries Science Research Institute Published

The aim of this study was to find the best location for establishment of rainbow trout culture and hatcheries farms on Zayanderood’s river region in Charmahal and Bakhtiyari province. This survey carried out over ten station along Zayanderood’s river. The result of physical and chemical analysis showd that the annual average of air temperature varied from 9.5oc o 10oc wehre the pH annual average value were between 7.5 and 8.8. the dissolve oxygen concentration in stations except in rainbow trout farm effluent were above 10 mg/l. the other chemical , pollutant as well as pesticides levels were under the limiting concentration for rainbow trout culture and Hatcheries activity . The plankton survey showed that the Bacillurophyta were the dominant group of phytoplankton where protozoa constituted the most abundant group of zooplankton the Benthic organisms sensitive to pollutant in particular Epirus were dominant group in all stations . In regard to fishes presence in river , five species of Ciprinidae , one species from Balitoridae and one species from salmonidae families were identified . The capacity for development of rainbow trout culture for tow phase period in Zayanderood’s river region with respect to self purification potential (self purification potential were determined from the oxidation of the effluent of the only active trout farm of the river region), minimum of 10 L/s water requirement for production of trout in concrete canal and pond system and 1L/S water need for production in semi circular closed system were estimated to be 5202 metric tons. Iranian Fisheries Science Research Institute Published

Kutum fish (Rutilus kutum) is an anadromous cyprinid species that spawns in adjusted rivers to the Caspian Sea. Many million fingerlings were artificially produced and annually released in these rivers specifically in Sefidrud River by Iranian Fisheries Organization. In this study were estimated the staying period of Kutum fingerlings in Sefidrud River and its diet and growth. A small piece of the caudal fin was cut as a tagging method. About 50000 and 5200 individuals were marked during July and September 2013, respectively. The marked fish had an average total length 53.2±5.6 mm and body weight 1.11±0.26 g and were released in river around two kilometers of the estuary. The sampling of fishes had been earlier started from Feb. 2012 and continued until Feb. 2013 at five stations. Four stations were along river from three Kilometer of estuary to estuary and one station was in right side of estuary in the sea coast. The results showed that marked samples after releasing time were distributed in all studied area from 3 kilometers of estuary to estuary but they migrate mainly toward Caspian Sea in a short time. However the marked samples were observed in estuary and the sea coast after 6 and 24 hours of their releasing time, respectively, Kutum fingerlings remained in Sefidrud river ecosystem in a longer time, at least until end of our sampling period i.e. 105 days. The coefficient of vacuity index of the natural feeding study was 0.0, 49.0 and 30.6 % for phytoplankton, zooplankton and benthos, respectively. The average of GastroSomatic index, intensity of fullness and condition factor were calculated 6.30±3.25, 174.6±153.2 and 0.92±0.09, respectively. A temporal and spatial variation on main food items were observed in gut content of fish fingerlings from different locations and seasons. Gut contents were generally included 59 genera of phytoplankton, 15 groups of zooplankton and 10 groups of benthos. Nitzschia, Navicula and Synedra were dominated among phytoplankton genera with 45.83, 18.02 and 15.99 %, respectively. Among zooplankton groups; the Rotaria, Moeina and Difflugia were dominated with 22.30, 20.86 and 15.83%, respectively. Chironomidae and Gammaridae were the main food items among fed benthic animals with 83.67 and 11.15%, respectively. Furthermore 48 phytoplankton genera, 32 zooplankton genera and 6 benthic families were identified in ecosystem of Sefidrud river. Bacillariophyta phylum (with 23 genus), Rotatoria (with17 genus) and Chironomidae family were dominated in each mentioned groups, respectively. It is concluded that the Kutum fingerlings stay in Sefidrud River for a long time, although most of them migrate to Caspian Sea during first month after releasing. However dietary indices were normal in studied samples, the condition factor index seems to be low.

Phytoplankton groups are very important producers in the Anzali wetland having a significant role in the quality and need to be constantly studied in term of their sequence and density. This survey was conducted at 6 stations between March 2011 and February 2012. According to the results, 67 different genera (22 Bacillariophyta, 26 Chlorophyta, 9 Cyanobacteria, 5 Cryptophyta, 1 Euglenophyta, 2 Chrysophyta, 1Dinoflgellata and 1 Xanthophyta) were identified. Most observed in Sorkhankol and Karkan stations with the annual average of 24.4±5.6 and 20.4± 5.4 cells/ liter respectively. The Bacillariophyta particularly Cyclotella was dominant in all of the stations, but high abundance of Cyanobacteria in Karkan station from July to mid-October caused the annual average of this phylum to be more than Bacillariophyta. The highest and lowest phytoplankton abundances were observed in September and December, respectively. The number of phytoplankton genera and diversity in this study were less than previous studies.

Anzali wetland is one of the most important places for spawning fishes and zooplankton groups are the first consumer in this ecosystem . they are the perfect food for the larvae of fishes. Zooplankton status was evaluated in 6 stations of different areas of the Anzali wetland during March 2011 to February 2012. Sampling was done by tube (PVC) and passing through of 30 micron planktonic net. The samples were identified and counted by invert microscope. According to the results were identified 60 Genus and 6 phylum (11, 31, 10, 2, 1, 1, 1, 2 genus of phylum Protozoa, Rotatoria, Arthropoda, Gastrotricha, Mollusca, Tardigrada, Nematoda, Porifera, Annelida) respectively. The results showed that the maximum annual average density of zooplankton was observed with 2497 number per litre in Karkan station and the population was more in the summer than in other seasons. Phylum of Rotatoria,, protozoa and superclass Copepoda formed 48, 45 and 6percent of the density espectively. According to the results the populationof zooplankton did not change much compared to past studies, excluding Protozoa but the diversity of all zooplankton groupe are declined very much. According to the statistical analysis Kruskal Wallis are not significant differences between density of zooplankton in different stations, months and seasons (p > 0.05),but significant differences were found in different phylum together (p < 0.05). Iranian Fisheries Science Research Institute Published

This research was conducted to finding of Cheshmeh-Ali and Shahcheraghi-Dam downstream areas potential for developing of aquaculture industry. The present study was conducted based on available information and data from monthly and seasonally sampling including geographical area, margin lands and fluctuations of river water, seasonal climatic changes view point of rainfall, temperature, wet, evaporation, wind velocity, sunshine hours, frost and also chemical and physical parameters of water including temperature, alkalinity, total hardness, chloride, calcium, magnesium, sodium, potassium, organic phosphorous and nitrogen, suspended solids, turbidity, water flow and flood conditions, and in addition phytoplankton and zooplankton communities, macrobenthic invertebrates, fishes, aquatic plants, amphibians, reptiles, birds. Results showed that the upstream and downstream regions of Shahcheraghi dam are not suitable for warm water aquaculture in earthen ponds. But view point of cold-water aquaculture, particularly trout, there are some good situations. Also it can be suggested different culture systems including of race way, octagonal concrete ponds, semi-circulation and circulation methods. But, due to water restrictions in the area, semi-circulation and circulation system is preferred. In ideal conditions can be produced about 1,600 tones of trout, if all the capacity of this area be used for aquaculture. Otherwise, in limited circumstances view point of exploitation possibility of the water, only about 700 tons can be produced. In addition, there were appropriate facilities in spring area of Cheshmehali for tourism industry, that it can be considered as priorities for economic development in the region. Due to the low sensitivity of the ecologically conditions, native or exotic aquatic species rearing in indoor methods can be recommended. Iranian Fisheries Science Research Institute Published

Reservoirs are one of the most constructions for control and water supply for different usage that could have various social an economical effects. The Khandaghloo dam reservoir with area of 100 ha located in Mahneshan city of Zanjan province and related to Parichay river watershed. Khandaghloo reservoir is valuable water body that the aim of its establishment was supply of water for agriculture farms. The reservoir has been studied for responsible and sustainable fisheries exploitation proposes. Results showed that the reservoir categorizes as eutroph to super eutroph based on different indices.Also phosphorous is limiting factor of the water body.Totally 42 genera from 6 phyla including green-blue algae cyanophyta, diatoms (Bacillariophyta), green algae, chlorophyta, euglenophyta, pyrrophyta and xanthophyta has been identified and cyanophyta was the dominant group that comprise 74.3 % of phytoplankton population. The zooplankton of the reservoir comprised 4 phyla and 20 genera. 1 genera of the protozoa and rhizopoda, 1 genra of the ciliophora ,15 genera of rotatoria, 2 genera of cladocera has been identified in zooplankton communities. Tubificidae and chironomidae has been identified in all months of the survey. The mean total length of crayfish was 130.5±20.5 mm ( 636) and mean weight was measured as 69.4±34.1 g with maximum and minimum weight of 1.9 and 207.2 g respectively .Total biomass of crayfish in Khandaghloo reservoir estimated as 3.4 tones with a range of 1.1–5.7 tones. But it is recommended not to harvest for at least two year due to high mortality of the populations.The fishes of the reservoir comprised common carp Chinese carp (silver carp, big head and grass carp) (released), Caspian kutum (accidentally released by fishery sector) and some endemic species as Siamahii. The catch of the reservoir fluctuated between 8 to 26 tones during 2000-2010.The fish production of Khandaghloo reservoir ranged from 167 to 324 kg/ha based on different methods that by consideration of 100 ha area of the reservoir, the total production of fish fluctuated between 16.7 to 32.4 tones. The fingerling restocking of Chinese carp in Khandaghloo reservoir with density of 1500 fingerling/ha recommended as 68% of phytoplanktonivorous fish (silver carp) ,12% zooplanktonivorous fish (big head), 6.6% of Crass carp and 10% of benthophagous fish (common carp).

The project was carried out between June of 2011 and November of 2012,8 laboratories of research center in Anzali (Plankton, Algae, Hydrochemistry, Physiology, Ichthyology, Bentose, Parazitology, Virology) and 7 laboratories of research center in Ahvaz (Clinical pathology, Plankton, Hydrochemistry, Physiology, Ichthyology, Bentose, Parazitology, Virology) were selected for accreditation. The main stages for establishment of the system consisted of: 1-Conducting a gap analysis to compare the present state of the laboratories with ISO/IEC 17025 2-Training General requirements for the competence of testing and calibration laboratories Validation of methods Estimation of uncertainty Internal audits 3- Performing of technical and management requirements 4-Submit of quality manual to ASCB center in England in order to accredit In August of 2012 The main results were including: 1-Increase the accuracy of measurement in laboratories 2-Improvement of the Repeatability and Reproducibility of the test methods 3-Traceability and standardization of test methods 4- Calibration of measurement instruments 6- Updating of test methods 7-Standardization of physical condition of the laboratories 8- Getting the certification from ASCB center in

15000 juvenile Indian majour carps (Labeo Rohita,Cirhinus merigala, Catla catla) imported (200 ) and transferred to the earthen ponds in Astaneh Fisheries Research Station , In order to assess the viability of rearing under the climatic condition of north part of Iran and also achieve some growth parameters from the larval stage to market size.The fry with 300 mg weight, were released in to 12 ponds.specimens were separated to tree experimental categories: 1= (30%indian carp and 70% chinees carp) , 2= (50%indian carp and 50% chinees carp) , 3= (70%indian carp and 30% chinees carp) .single chinees carp production were used as control . fishes were fed with artificial food and also with the natural products of the ponds which were enriched with organic fertilizers, after being equally stocked in the ponds .During the experiment, oxygen level ,PH, turbidity, and temperature were measured . Monthly fry samples were taken, for weight and length biometrical analysis and also determination of the weight gain percentage, average daily growth rate, specific growth rate. Results have indicated adaptations and considerable growth in this species, with an increase from the initial weight of 300 mg to an average of 13.5±1.6 mg in 50 days period until the end of November for fingerlings. Also the average weight of growing phase (second year of production ) was 647g. for Labeo Rohita ,420 g. for Cirhinus merigala and 734g. for Catla catla. The special growth rate(SGR)in Roho was 4.51 %.and 3.9 % for merigal and6.2 % for Catla while for Chinees carps SGR was 4.9, 6.7, 7.6 and 5.8 for silver carp,grass carp, common carp and big head respectively. Results revealed that the Indian majour carps compatibility with the condition in Gilan province was succesfull and the combination of species and optimization of their compatibility were remind for futhre studies. Iranian Fisheries Science Research Institute Published

The Taham dam reservoir has been established in order to provide drinking water of Zanjan population as far as 15 km in a mountain region at 1900 meter altitude with a 317 ha surface area. This study was conducted on biotic and a biotic factors in order to recognize of aquaculture possibility within drinking considerations. The results showed the less abundance of phytoplankton with 2 million/l. where abundant of zooplankton was 266 /l. Bacillariophyta and Chlorophyta belong to phytoplankton and Rotatoria belong to zooplankton were dominated among identified plankton phylum. There were identified 45 and 32 genus of phytoplankton and zooplankton respectively. There were identified 5 groups of benthos that Tubificidae, Hirudina had the most frequency, and the biomass of benthos was varied from 1.1 to 23.7 g /m^2. The ichtiology survey showed presence of 6 species in the lake that Alburnoides bipunctatus, Capoeta capoeta, Leuciscus cephalus were the most abundance in the catch. L. cephalus was recorded with the maximum size of 870 g while the most frequent weight class was 150 450 g for C. capoeta,, L. cephalus . Diet survey showed the adequate feeding of fishes in lake also the observation of leech in trout guts was very considerable. The reproduction study displayed that a partial of matured fishes were succeed in breeding. Leuciscus cephalus have been known as a typical species with commercial size and high abundance which will be needed a fisheries management in Taham Lake to sustainable exploitation. The hidrochemical results indicated low nutrients values while total nitrogen was varied from 0.32 to 0.61 mg/l. and the Chl-a was varied from 7.9 to 25.9 μg/l. The oxygen amount was 4.5 to 8.4 mg/l even in 65 meter depths. Total hardness average was about 149 mg/l where the Ca and Mn were measured in a low values. Trophic model in Taham lake showed the early stage of mesotrophy while other lakes and wetlands in north of Iran had been progressed in mesotrophic level.

Anzali wetland at south west of Caspian located along of North West and southeast and with its unique feature were add on the Ramsar convention list in 1975. There were recorded a high rich of fauna and flora including 276 plant species, 23 reptiles and amphibians, 60 fishes, 26 mammals and 195 birds. Anzali wetland were encountered with numerous disorder with the eutrophication and the early dismissing. The first studies on Anzali wetland started by many international institutions in 1964. In this study the data of biotic and abiotic factors in Anzali wetland analyzed which belongs to different sites (15 to 38 stations) during 1991 to 2000 and were sampled seasonally or monthly in different years. The results showed the increasing trend of phytoplankton abundance from 7.9 to 66 million C./l. and the western part had the most abundant. The Cyanophyta had the most development than other 7 phylum observed in the area. In Anzali wetland identified 143 phytoplankton genus that 9 genus dominated in more than 80 % replicates and 7 genus had the abundance of more than 5 million cell/l. The Zooplankton abundant increased from 580 to 2200 ind./l. The Rotatoria had the most abundant followed by Copepoda. There was identified 104 zooplankton genus that 5 genus were dominated in more than 80 % replicates and 11 genus had the abundance of more than 30 ind./L. The chlorophyll a varied from 8.8 to 50.2 μg/l. and had a increasing trend after 1996, meanwhile it was measured higher than 25 μg/l in most of the stations. The results of benthic study showed that the Chironomidae and Tubificidae were observed more than other organisms which comprised 12.2 to 23.5% of total biomass of benthic organisms in studied period. The range of biomass was 1.1 to 7.8 g/m2. The ichthyologic survey showed presence of 60 species that 11 species were exotic. 28 species belong to freshwater, 17 species were anadromous and 8 species were resident in estuary. The highest and lowest fish catch were 640 and 288 ton in 1994 and 1999 respectively and it was about 500 ton at the end of period. The hydrochemical factors had the various fluctuation so that the nutrients parameters had a significant difference over studied period. Total nitrogen was varied from 0.78 to 1.41 mg/l and total phosphorus varied from 0.05 to 0.1 μg/l.. The oxygen dissolved amount was from 4.6 to 8.7. EC was between 3 to 5 ms/cm during September and October that indicated of Caspian water projection. According to geographic position of station, all biotic and abiotic data, were arranged. The data bank is used by Idrisi software to produce of necessary maps. Analysis of data showed that there must be a responsible department with a vast authority. Conservation and eutrophication prevention of Anzali wetland connect to special attention to catchment area and landuse management of the wetland. Also there is an urgent need for well-developed technologies and managements to reduce the organic pollution and its environmental impacts on the Anzali Lagoon.

Use and enrichment of live food resource in fish farms have been interested and highly demanded. Crustacean are one of the important groups. The Pontogammarus maeoticus dominated in southern Caspian Sea shore with a high abundance. This study was designed in order to adaptation and usage of amphipoda in fish culture ponds. The first part have been surveyed the laboratory experiments including of; to increasing and developing of P.maeoticus in 200 litter container, the effects of salinity on growth and survival of amphipods in many aquariums, the culture of common carp with amphipods and growth determination of them. Chemical composition analysis of P.maeoticus and carps fed by amphipods in compare to cultured carps from ordinary ponds. Due to concern about common healthy the heavy metal concentration has been measured in P. maeoticus, carp which were fed by amphipods and the cultured carps in earth ponds. In second phase; the adaptation of two amphipods species, P. maeoticus and Obesogammarus acuminatus was studied in fish ponds where some cages with sandy soft substrate had been provided for amphipoda replacement. Also a small surface of ponds surrounded by net and covered by Azola plant, a habitat suitable for to putting of O. acuminatus. Production of amphipoda had not the successfully results in large tanks. Aquariums with Caspian sea water had the prosper results where the specimens were breeding and developing properly, even though in some aquarium with freshwater increased the amphipods number. The chemical composition had not significant difference between two kind of cultured carps while the organic component in amphipoda had a high quality. The better quality of cultured carp by amphipod diet have been confirmed by organoleptic test. The results of heavy metal measurement in amphipoda showed a high concentration which some of them were transmitted to cultured carps. Result of amphipoda replacement in cage was not satisfy and the specimens were died after some days. According to hydro-chemical parameters the oxygen poorness and high trophy levels were the affective factor to abolish of specimens in cages. It seems that there are many type of P.maeoticus that can be adapted in different salinities. The molecular differentiation should be investigated to choose the suitable type of this spices for utilization in freshwater fish ponds. In other hand it can be used in fish culture ponds that will be supplied by brackish water. Iranian Fisheries Science Research Institute Published

The Caspian goby, Neogobius caspius, is an endemic species of Gobiidae family in the Caspian Sea and it has ecological importance (as food for Caspian commercial fish such as sturgeons). The main aims of this study are, studying distribution, length, weight and age structure, sex ratio, diet, reproduction biology and morphological characters of this species in Guilan coast at waters of the Caspian sea and the sampling has been done monthly from Oct. 2005 to Sep. 2006 in 4 station from Astara to Chaboksar, with bottom trawl which had 12.5 meter length, 4.7 meter gape width and 2 mm mesh size in code end. The results showed N. caspius abundance is 9.82±11.93% of Gobiids and 7.92±10.10% of total fish numbers sampled in the study area (13824 specimens belong to 16 fish species) and there were significant differences among stations and seasons. CPUA of N.Caspius was estimated 52.5±105.9 ind/hec and 412.7±770.7 g/hec and there were significant differences among stations and seasons. Maximum body weight, total length and age were measured 65.10 g, 176 mm and 6 years old with an average 8.74±9.9 g, 84.83±28.4 mm and 1.83 years old, respectively and maximum age of males and females was 6 and 5 years old respectively and there were significant differences among stations and seasons and between sexes. It was estimated algometric growth model from length-weight regression, coefficient of K Von Bertalanffy growth model was estimated 0.42 and 0.68 in male and female, respectively. Sex ratio was 1.27 female to 1 male. Coefficient vacuity, relative gut length and intensity of 169 fullness were 8.72%, 0.76±0.17 and 267.7±263.3 for, respectively and Caspian goby fed on 30 different prey consist Zooplanktons (8 types), Benthic animals (15 types) and fishes (7 types) and young and yearlings have fed mainly mixed food (zooplankton and benthic animals) and adults on zoobenthose. Gammarids, Bivalvia, Cumaceae and Vormes constituted 44.7, 38.9, 24.8 and 19.7 % of prescence in full-gutted samples respectively, they were mainly preys (number and weight), hence this species is considered as euryphagus, carnivorous, benthphagus species. It was determined, Caspian goby spawns from March until last June, males and females take part in spawning in 2.8g and 65 mm and 1.3 g and 52 mm, respectively. Length at 50% maturity (LM50) was 80.2 and 77.5 mm in males and females, respectively. Maturity took place at 2 years old for both sexes, too. The absolute fecundity was estimated 109-1350 (451.6±216.3) eggs and relative fecundity 18-80 (36.8±9.2) eggs per one grams of body weight and diameter of ripe eggs was measured 1.31-2.60 (2.18±0.19) mm. Morphologically, there were 15 morphologically significant statistical differences between males and females and 15 differences among stations, sexual dimorphism was observed, too.

Mnemiopsis leidyi was sampled from December 2003 to March 2005 in 11 stations located along four regions Anzali, Khazarabad, Tourkman and Gorgan Bay using METU net in the Iranian coasts of the Caspian Sea. Study of stomach contents of M. leidyi showed that Acartia sp. belonging to Copepoda and Lamellibranchia sp. had the highest frequency comprising 66% and 13% of food items taken by the organism respectively and the least food items taken were Balanus nauplii, Rotatoria, Tintinnopsis and Podon polyphemoides. The maximum mean abundance of food item was Acartia sp. which was shown to be present in stomach content of M. leidyi caught in different depths, seasons and regions in the Iranian coasts of the Caspian Sea. For the M. leidyi larvae, the highest amount of food item was Acartia sp. and Lamellibranchia sp. with an average of 44% and 32% and the maximum abundance of food item for juvenile and mature M. leidyi was also Acartia sp. with an average of 67.5% and 66%. The results showed that the main food item for M. leidyi is Acartia sp. of the Copepoda. Hence, M. leidyi feeding has an important effect in declining zooplankton populations.

Mnemiopsis leidyi is one the species of comb-jelly. It belongs to the Ctenophore phylum and Lobate order. It is a purely marine, free-swimming animal with a transparent jelly-like walnut-shaped body, which was transported from the Black Sea into Caspian possibly at the end of 1990s. This species is food rival of pelagic fish. It has been reported that the ctenophore caused the dramatic decrease of zooplankton and pelagic fish stock in the Black Sea. In this study, sampling on Mnemiopsis leidyi, zooplankton, phytoplankton was conducted from December 2003 to March 2005, from a total of 11 stations located along four transects (Anzali, Khazarabad, Tourkman and Gorgan Bay) by METU net in the Iranian coasts of the Caspian Sea. Clupeonella catch was done by light fishing with fishing vessel in Anzali region. The results showed that the biomass of M.leidyi had some fluctuation in different seasons and its maximum biomass was recorded in summer with a figure of 524.4±156.2 g.m^2 Tourkman region and the minimum biomass was observed in winter with a figure of 5.15±1.81 g.m^2 in Anzali region. Study of stomach of Mnemiopsis showed, that Acartia (belonged of Copepoda with 66 %), lamlibranchia (13 %) has the highest frequency and the lowest were Balanus nauplii, Rotatoria, Tintinnopsis and Podon polyphemoides. The maximum mean abundance of zooplankton was 29368±24318 n.m3 in winter (Anzali region) and the minimum was recorded 4170±5014 n.m3 in summer (Tourkman region). Copepoda was dominant zooplankton in the Iranian coasts of the Caspian Sea. Chrysophyta with 150000000±440000000 n.m3 and Euglenophyta with 260000±521000 n.m3 had the highest and the lowest frequency respectively in the Caspian Sea. The main foods of Clupeonella were Acartia with 80 %. The survey of stomach of Clupeonella showed that the feeding of these species was not good and the highest fullness index was recorded 220.95±314.67. These results showed, the main food item of Ctenophora and Clupeonella were Copepoda (Acartia). It seems, the impact of Mnemiopsis leidyi feeding has been the important factor in declining zooplankton populations, Clupeonella stocks, and also increasing of phytoplankton abundance.