An investigation of some biological aspects of three species: tiger toothed croaker, Otolithes ruber, Javelin grunter, Pomadasys kaakan and black pomfret, Parastromateus niger in the Oman Sea for optimizing fishing season

During the years 1382-83, some biological aspects of three species Tiger-toothed Croaker, Otolithes ruber, Javelin grunter, Pomadasys kaakan, Black Pomfret, Parastromateus niger, have been investigated in the Oman Sea along Sistan-O-Baluchistan province. Based on the frequency of developed maturity stages (IV, V), a prologed spawning activity extending from August to March was determined for O.ruber, and the Gonadosomatic Index (GSI) suggests two peaks:the minor one in October and the major one in March-April. Comparison of Hepatosomatic Index (HI) and Condition factor (Kn) with the peak spawning indicated a reverse relationship. According to length at first maturity (Lm50%= 40cm) and exploitation of fish at length 42cm above, the stretched optimum mesh size of nets was calculated to be 100mm. On analysis of stomach food item, fish group dominated (80%), which of them Anchovy accounted for 40% of the total frequency. Comparison of mean length between the years 1374-75 and 1382-83 showed 4cm in decrees. Population dynamics parameters were determined through length based modals and the exploitation rate was estimated to be E=0.6, suggesting high level exploitation. The usal streched mesh size of nets(constructed from multifilament webbing) for capturing O.ruber were less than the proposed optimum mesh size of nets, indicating 78% of the total landings were smaller than Lm50%. Total landings in 1381 have increased up to 15% when compared to those of the year 1376. Despite the decrease of total efforts (Panel.day) by 37%, the mean value CPUE has increased up to 82%. Regarding Pomadasys kaakan species, a year-round spawning activity has been observed, with two peaks: A major one in April and an aminor one in September. As those of O.ruber species, there was an inverse relationship between HI and Kn with the peak spawning activity. Based on the length at first maturity (Lm50% = 44cm) and capturing fish of the length at 46cm and above, the stretched optimum mesh size of nets was calculated to be 149.6mm. According to analysis of stomach contents, fish group accounted for 35% of the groups studied, which of them , Largehead hairtail, Trichiurus lepturus linnaeus, constituted 52% of the total frequency. In addition to estimation of population dynamics, the exploitation rate was estimated to be E= 0.49. Majority of the species catch was made by mesh size of nets used for O.ruber of which 133mm mesh size accounted for the level (30%). Information on length distribution showed that 60% of the total fish landed was below Lm50%. Total landings in 1381 decreased to 10% in comparison to 1376.Total fishing efforts and CPUE also decreased to 33% and 24% respectively. For parastromateus Niger, There was a long period spawning activity from March to December, with two peaks: A major one in August and a minor one in March. According to Lm50% (39cm) and catching of fish 39cm above, the stretched optimum mesh size of nets was calculated as 167.7mm. Based on stomach contents, ring-shaped worms and larval shrimp equally made 29% of the total frequency showing the highest contribution. Comparison of mean length indicated 3cm in decrease in 1382-83 when compared to 1374-75. Population dynamics parameters were estimated and the exploitation rate was estimated to be E = 0.54. The usual stretched mesh size of nets for P. niger was 146mm and 81% of the total fish landed were smaller than Lm50%.In 1381,total catch of the species increased four and a half-fold in comparison to 1376, while total efforts decreased up to 28% and CPUE increased two and a half-fold

Monitoring of tuna resources (yellowfin and skipjsck tunas) in Oman Sea along Sistan & Balouchestan coastal waters

Collecting of biometric parameters and catch and effort data were made for yellowfin and skipjack tunas from artisanal gillnet and industrial purse seine fisheries during the years 2002-2004 in Oman Sea along Sistan and Balouchestan coastal waters. The previous available data was used for the purpose of better monitoring the resources. The frequency of maturity stages and GSI values obtained from yellowfin showed a spawning period from February to May, peaking in April-May. For skipjack, the data indicated a long spawning period which beganed in December with peaking in April-May. LM50% was obtained as 83.1 and 62.4 for yellowfin and skipjack tunas respectively. Sex ratio by size group showed a predominance of males with larger fish. Analysis of stomach contents showed a significant proportion for the both species. The composion of food contents by occurrence method revealed that fish were the most dominant food items by year for the specise. Presence of squilla, crabs, shrimps (Larval stage), belonging to Peneaidea family, in large quantities were the oblivious food items so that they had not been reported by previous studies. Blooming of squilla, Natosquilla investigators, in the western Indian Ocean provided a situation to be observed in large occurrence in yellowfin and skipjack stomach contents. The ratio was more in yellowfin stomachs when compared to skipjack ones which accounted for 38%, 19% and 35% of the total stomachs studied by the study year. The shrimps prey were only observed in skipjack gut contents (with exception of one case in yellowfin stomach) which were the second major component in 2002 and 2003(24% and 17% respectively). Comparsion of mean length showed a sharp decrease from 1992 to 2004 for the species. Regarding yellowfin the mean length from 93.2 cm FL in 1992 reached to 83.2 cm FL in 2004 and from 64.95 to 58.51 cm FL for skipjack. In spite of decreasing mean length for yellowfin, the value increased in 2004 in comparison to 2003 which was in agreement with Indian Ocean data. Comparative analysis of length frequency with LM50% indicated that immature fish were the major part of the catch. There are available information on population dynamic parameters. A comparative analysis of CPUE,s (kg/panel.day) from artisanal gillnet fishery for yellowfin and skipjack tunas revealed a decreased value by fishing craft class in 2005 when compared to 1998 data, but increased in 2003. Increased trend of the species catches by fishing craft class was due to increased fishing effort. Analysis of the statistical catch and effort data for the study years, irrespective of fishing craft class, showed that total landings of the species have increased 4.4 fold in spite of attaining CPUE to 7% in decrease which was a consequence of increased fishing effort up to 4.7 fold. The CPUE, s (tons / positive set) from industrial purse seine fishery increased in 2003 and 2004(39% and 10% respectively), but declined up to 54% in 2005. The trend is in agreement with purse seine fishery data from Indian Ocean where the increased values were attributed by larger size of yellowfin. The purse-seine fishing ground data revealed that the major sets were made in Persian Gulf, whereas a shift towards Oman Sea in eastern part of Sistan and Balouchestan coastal waters is recommended to be a suitable fishing area for the first half of year and towards offshore waters in Indian Ocean for the second half of year. For attaining a sustainable fishery system, it is recommended to regulate the gillnet mesh size and introduce longline fishery in the area along with stopping any further increased fishing effort in artisanal gillnet fishery

Hydrology and hydrobiology data analysis collected during 1998-2007

Annually, many data of hydrology and hydrobiology of the southern Caspian Sea at Iran's coasts were collected by Caspian Sea Research Institute of Ecology. The data which had been collected by researchers submitted annually in several reports but has not been processed all at once. Fluctuations of various parameters were surveyed and the relationships between them were analyzed. The main goal of this research is to analysis the data were obtained from 1994 to 2006 and show changes the concentration of various parameters in the Caspian Sea. Physicochemical data indicated that the average trend of transparency and salinity was decreased from 1994 to 2006 annually, where the salinity value was decreased from 12.37 ppt (part per thousand) to 11.5 ppt. The average of dissolved oxygen was increased from 6.4 to 8.6mg/l. pH has slightly fluctuated from 8.15 to 8.31. However, with increasing depth from surface to bottom, the average of dissolved oxygen was sharply decreased (DO concentration in surface and 800 m was 7.18 and 1.45 mg/l, respectively). The trend of salinity and pH fluctuation was very slow with depth but the salinity has an increasing with incrementing of depth but pH has a decreased trend. The average of organic and inorganic phosphorus and TP was nearly increased. The average of Nitrate and Silica sharply increased comparing to depth but the average of Nitrite and organic Nitrogen decreased. The results showed that the temperature fluctuation in different water layers was low in winter but the dramatic decreasing of temperature was occurred at 10-20 m (in spring), 20-50 m (in winter) and 50-100 m (in autumn). With increasing of depth (Slope of the Sea), transparency and salinity values have an increasing while DO and pH showed decreased. As a whole, 335 species of phytoplankton were identified, there are 70 species in advance as these species were not seen in this period but 96 of novel's species have been recorded. The lowest and the most of phytoplankton biomass was recorded in 2006 and 2001 while the biomass was 59 and 1034 mg/m^3, respectively. Albet, the lowest biomass was recorded at the depth of 100 m (24.1 mg/m^3) but the maximum was observed in surface layer (1344.1 mg/m^3). The average of phytoplankton biomass was increased after arrival of the ctenophore. There was a significant difference between the average of biomass in different seasons before and after of the ctenophore invasion (P0.137, P>0.782). Before the presence of ctenophore, the worms had been constituted a dominate group with an approximately %45 of total abundance and also %20 of their biomass. After this period, their frequency was sharply increased (more than %85) but the maximum value pertains to Cardidae (more than %90). The species diversity, evenness and richness were varied between .69-2.51, 0.23-0.63 and .011-3.79, respectively. AMBI software, Shanon-Viner parameter was moderate in all seasons from 1994 to 1996 but this parameter was reduced in a bad limit (boundary) in the most seasons from 2002 to 2005. The main parameter of M-AMBI consists of several parameters and also approximately showed similar changes such as Shanon -viner parameter. On basis of this parameter, the ecological quality condition of Caspian Sea was superior limit in all seasons from 1994 to 1996 but after the following years were decreased from good to moderate limits (After the presence of ctenophore). Relationship between abiotic variants and phytoplankton indicated that there was a direct relationship between transparency and salinity while there was a powerful and reversal significant relationship between transparency water temperature, transparency in organic Nitrate, phytoplankton number and transparency phytoplankton biomass. The comparison between different variants average in two periods (before and after the ctenophore invasion) indicated that the average of Kilka catch was decreased, the relative frequency of clupeonella engrauliformis and clupenoella grimmi was sharply reduced but the relative frequency of Clupeonella cultriventris was sharply increased, the species diversity, evenness and richness and the number of zooplankton species were sharply decreased, the average of biomass and transparency was sharply reduced, the average of dissolved oxygen and liza saliens or liza auratus catch were increased. These difference were often significant (P<0.05). Therefore, with the ctenophore invasion into the Caspian Sea, the primary production was increased, the biomass value of zooplankton and specially Kilka which fed on zooplankton were sharply decreased while the fish such as Rutilus frisii kutum and mullet (Liza salins or Liza aurratus) which fed on benthic were increased

The study of feeding, reproduction and biological parameters of kilka fishes in the Iranian waters of the Caspian Sea

The overfishing and changing environmental following the introduction of the comb jelly Mnemiopsis leidyi in the Caspian Sea, the population structure has a strong influence on kilka fishes in the Caspian Sea and therefore to in this investigation which had been done in commercial catch regions (where discharged theirs catch) in three ports Babolsar, Amirabad (in mazandaran) and Anzali (in Guilan), stimated catch and catch per unit effort, the age structur of catch, length- weight relationship, von Bertalanffy growth parameters, condition factor, sex ratios, maturity stags, spawning and feeding. The result shown that catch of kilka in Iranian coastal in 2012 decreased from 24080 ton to 22696 ton in 2013. But CPUE increased was 2.7 ton (Vessel ×Night) and there was no significant changes. Common kilka was the predominant all months of the year, 98.1 and 98.9 percent in 2012 and 2013 respectively. The mean length was 104.4±10.5 and 101.6±11.2 at the same time and range length 92/ 5 – 117/5 mm were the dominant population(about 75%). Relative abundance of fish less than 77.5 mm and more than 127.5 mm is very low. Age abundance during this period have not been substantially changed and always fishes with 3 and 4 year olds had the highest frequency73.6 and 73.5 percent respectively. The parameters of the Von Bertalanffy growth curve were (8.141) 048.1 for common kilka. The instantaneous coefficient of natural mortality (M) was 0.506 yr-1. The instantaneous coefficient of fihing mortality and total mortality were 0.694 yr-1 and 1.2 yr^-1 , respectively. The exploitation rate of common kilka varied during 2012-2013 between 0.41-0.50. The mean condition factor 1.41±0.14 (n=5801) and 1.38±0.16 (n=6754) at the same time respectively. According to statistical analysis Anova oneway were a significant difference between condition factor at the same time . Main prey common kilka was Acartia tonsa accounting for over 80%. It seems Common kilka due to a decrease in the frequency of other zooplankton species depend more than ever on Acartia tonsa and this species is probably a concentration of prey for Common kilka

Biological aspects of kilka (age, growth, feeding and reproduction) in southern of Caspian Sea

In the changing environmental of the Caspian Sea specifically pelagic zone following the introduction of the comb jelly Mnemiopsis leidyi has been continued ,particularly kilka catch ,biological characteristic and feeding . In this investigation which had been done in commercial catch regions (where discharged theirs catch) in three ports Babolsar ,Amirabad (in Mazandaran) and Anzali (in Guilan), estimated catch and catch per unit effort, the age structure of catch ,length- weight relationship, von Bertalanffy growth parameters, condition factor, sex ratios ,maturity stags ,age at first capture and spawning and feeding .The result shown that catch of kilka in Iranian coastal in 2006 decreased from 22300 ton to 16700 ton in 2008.But CPUE increased from1.7 ton (Vessel ×Night) to 2.5 ton at that time due to dropped effort .The length frequency of kilka is close and the juvenile fish did not see in catch as increased the length mean (P>0.000).The age frequency had the same situation as fish low than 2 years did not see for anchovy and bigeye ,so collapse juvenile stock cause poor recruitment in the species .The parameters of the von Bertalanffy growth curve were For common kilka L_∞= 136.5mm k= 0.249y t0= 1.890y Q= 3.883; For bigeye kilka L_∞= 131.7mm k= 0.346 t0= 1.123y Q= 3.688; And for anchovy kilka L_∞= 148mm k= 0.375 t0= 1.243y Q= 3.814 The exploitation rate of anchovy, bigeye and common kilka were 0.51, 0.58 and 0.6 respectively. The highest of GSI recorded in May and March for common and bigeye and in Jul, Nov for anchovy kilka .Main prey was Acartia tonsa by anchovy and common kilka and Cypris balanus by bigeye kilka. We concluded that the ecological problem causes by Mnemiopsis leidyi as well as overfishing has been collapsed kilka stocks, particularly anchvy.so sustainable fisheries management and conservation biodiversity in the Caspian Sea are real challenges now

The study of fluctuation of large pelagic stock (yellowfin tuna, skipjack tuna, longtail tuna, Narrow-barred Spanish mackerel) in order to optimum exploitation in the Persian Gulf & Oman sea

The study of fluctuation of large pelagic stock (yellowfin tuna, skipjack tuna, longtail tuna, Narrow-barred Spanish mackerel ) in order to optimum exploitation in the Persian Gulf & Oman sea This study was carried out from 2005-07 in order to acquire some biological characteristics and population dynamic parameters for stock management and responsible fisheries. Thunnus albacares (yellowfin tuna), katsuwonus pelamis (skipjack tuna), Thunnus tonggol (longtail tuna) and scomberomorus commerson (Narrow- barred Spanish mackerel) were sampled. In total, length frequency of 9345 specimens of yellowfin tuna were analyzed. Size range was 37-172 cm. Teleost fishes were the most dominant prey species observed in this study (42%), Occurrence of Potunus Pelagicus was found to be the second (28%).Sthenoteuthis oualaniensis (22%), Natosquilla (5%) and octopus (3%) also were identified in the gut content of the yellowfin tuna. Length of maturity (50%) of yellow fin tuna was estimated 77.2 cm and spawning season was started from May. 8443 specimens of skipjack with size range of 32-90 cm were sampled. 48% of food items were teleost fishes. Squid and shrimp were also identified. Spawning season was begun from June. Growth parameters & fishing mortalities of yellow fin tuna and skipjack tuna were also estimated. Size range if longtail tuna was from 26-125cm Length infinity was estimated 132.3 cm with growth parameter of 0.35 per year. In total 10451 specimens of narrow- barred Spanish mackerel were sampled. Size range was from 20-164 cm. Teleost fishes were the most dominant prey species observed in the study (91.3%). Crustaceans (0.6%) and Indian squid (0.2%) also were identified in the specimens. Length maturity (50%) was estimated 83.6cm

Spatiotemporal and estimation of washed out seaweeds biomass in Sistan and Baluchistan coasts

In order to studing and determination of Seaweed biomass in the Oman Sea coast (Sistan & Baluchestan Province), according to obtained reasults and experiments and observations on seaweed studies in 15 years ego, Beris, Chabahar, Pozm and Tang were high density zones and Jood and Lipar were low density zones in west and east of chabahar respectively that were selected for study stations. Total length of sistan and balochistan coasts from Gwatr area with geografical position 25˚ 10′ N & 61˚ 30′ E to Mydani with geografical position 25˚ 24′ N & 59˚ 5′ E were 354.3 Km. Among this length, 54.6 Km were rocky coast and 299.7 Km were sandy coast. Among this, 18.2 Km were high density zone and 281.5 Km were low density zone. Washout Seaweeds area in intertidial zones determind by measuring and recording of geographic positions by meter and GPS, then were obtained 2 transects determind with equal distance in high density area and 1 transects in low density for monthly sampling. The length of these transects were 100 meter and cross of Each transects were seaweed washed out average. The transects divided to 10 bluck and sampling were done randomly monthly from 5 bluck or 50 persent. The samples were transfered to the lab and the weight of each species was obtained after being cleaned, and separating. The biomass of each species per area unit and in the total area was obtained after determing the average weight of species and also determind geografical position by GPS. In relation to this project were done water sampling for recording of fisical chemistry factors. Total data for analysis recorded in this computer. During this research 9 species were collected. Among these seaweeds, 2 species green algea (composed of 2 families and 2 orders), 6 species brown algae (composed of 3 families and 3 orders) and 1 species red algae were identified. Wet biomass of Sargassum in the total area of Sistan & Baluchestan coasts were 445.9 ton in 2012. Among this biomas, 269.1 ton (%60.35) high density area (Beris 112 ton or %25.11, Pozm 83.7 ton or %18.76, Chabahar 59 ton or %13.22 and Tang 14.5 ton or %3.26) and low density zone 176.8 ton (%39.65). Monthly average were estimated about 74.3 ton (high density zone 44.9 and low density zone 29.5 ton). The maximum biomass was obtained 270.4 ton (high density zone 155.5 and low density zone 114.9 ton) in Azar and minimum biomass was obtained 3.5 ton in Esfand. At last, were suggested, This project were done in persian gulf coasts nessesery

Biomass estimation of demersal resources in the Persian Gulf and Oman Sea by Swept Area Method

Regarding to monitor of demersal resources in the Persian Gulf and Oman Sea, and also biomass and CPUA estimation of them, a series of research cruises (5 cruises per year) were carried out by R/V Ferdows-1covering the area from 49 00 E in the west (Khoozestan provice) to 61 25 E in the east (Gwater) in a 5 years program form 2004 up to 2008 (no cruise in 2006). The study area was stratified into 17 strata (A to Q) of which 10 starta (A to J) were in the Persian Gulf and 7 strata (K to Q) were in the Oman Sea, covering the depths of 10-50m in the Persian Gulf and 10-100m in the Oman Sea. A total of 316 stations were randomly selected. The biomass and CPUA were estimated by Swept Area method. The comparison between two regions indicated that the percentage of density of demersal fishes in the Persian Gulf during years 2004, 2005, 2007 and 2008 were 3.3, 3.9, 2.3 and 2.4 times more than the Oman Sea and totally 70-80% of total biomass was calculated for the Persian Gulf. Also a comparison among 17 starta, the highest biomass was found for starta C & D in the Bushehr province waters. The amount of CPUA for both regions of the Persian Gulf and Oman Sea was compared and it was concluded that in years 2004 and 2005, the mean CPUA in the Persian Gulf was partially higher than the Oman Sea with 1.06 & 1.20 times more; and on the contrary for the next two years this value was higher in the Oman Sea with 1.3 times more. The highest CPUA of demersal resources for the Oman Sea belonged to the strata K & O for years 2004, 2007 and 2008 and for year 2005 was for L and strata. It can be concluded that the north-west of Oman Sea has the best condition of biomass of commercial and non-commercial species and the O stratum will be in the second ranking. With review the mean CPUA in different depth-layers for years 2004, 2005, 2007 and 2008, it was concluded that with increasing the depth, the mean CPUA is decreased in which the CPUA values in depth-layer 10-20m for these years were 8.3, 3.0, 2.1 & 1.6 times more than depth-layer 50-100m. The comparison of mean CPUA for 10 strata of the Persian Gulf showed that in years 2004 and 2005, the mean CPUA of demersal fishes in the Hormuzgan province waters was higher than in Bushehr province waters (1.2 times more). In total, the highest maen CPUA belonged to F (Naiband to Mogham) and G (Mogham to Farour) in Hormuzgan waters. On the contrary, in years 2007 and 2008 this value in Bushehr waters was 1.3 times higher than western part of Hormuzgan waters with the highest value in D stratum(Boordekhoon to Dayyer). Also the comparison of mean CPUA for different depth-layers, it was found that the mean CPUA has ascending trend with increasing the depth, with the highest value in depth-laer of 30-50m in which contains the 55-68% of total biomass. The lowest biomass is found in depth-layers of 10-30m. Totally, the minimum CPUA and biomass for both commercial and non-commercial species belonged to a stratum located in Khouzestan province waters and it was shown the over-exploitation of resources in this area. The comparison between commercial and non-commercial groups in both ecosystems , it was concluded that the density of commercial species was higher than non-commercial ones , and in all years the Persian Gulf indicated higher values than the Oman Sea

Biomass estimation of demersal resources in the Persian Gulf and Oman Sea by swept area method

Regarding to monitor of demersal resources in the Persian Gulf and Oman Sea, and also biomass and CPUA estimation of them, ten research cruises were carried out by using R/V Ferdows-1 equipped with bottom trawl, covering the area from 49º 00´ E in the west (north-west Persian Gulf) to 61º 25´ E in the east (borderline with Pakistan) from 2012 to 2014 The study area was stratified into 17 strata (A to Q) of which 10 strata (A to J) were in the Persian Gulf and 7 strata (K to Q) were in the Oman Sea, covering the depths of 10-50 m in the Persian Gulf and 10-100 m in the Oman Sea. A total of 316 stations were randomly selected and the biomass and CPUA were estimated by swept area method during this three years period, the strat A and B weren’t covered. The comparison between two regions indicated that the percentage of density of demersal fishes in the Persian Gulf during years 2012, 2013 and 2014 were 1.0, 1.4 and 1.6 times more than the Oman Sea and totally 50-60% of total biomass was found for the Persian Gulf. Also a comparison among 17 strata the highest biomass was found for K region (Sirik to Jask) in the Oman Sea in 2012 & 2014; and C region (Genaveh to Bordkhoon) in 2013 in the Persian Gulf. The same comparison was done for CPUA of commercial, non-commercial and total in both water bodies and it was found that in years 2012 to 2014 the region K (Sirik to Jask) in the Oman Sea and Stratum Q (Bersi to Gwatr) had the highest value of CPUA. On the contrary, the stratum M (Biahi to Galak estuary) showed the lowest value of biomass for both commercial and non-commercial fishes. With review the mean CPUA in different depth layers for years 2012, 2013 and 2014, it was concluded that in the Oman Sea with increasing the depth, the mean CPUA is decreased and the lowest CPUA belongs to depths of 30-50 m The comparison between commercial and non-commercial groups in both ecosystems, it concluded that the density of commercial species were higher than non-commercial ones; and for years 2009, 2010 and 2011 the commercial species consist of 63.4, 65.0 and 59.7 % of total biomass. In all years the Persian Gulf indicated higher values than the Oman Sea. The most abundant fishes were Rays, Ribbon fishes, Carangids, Grunts, Japanese threadfin bream, Lizardfish and Barracuda for both Persian Gulf and Oman Sea

Survey and feasibility study for the introduction of native fish and non- native fish for cage culture in the southern part of Caspian Sea

The aim of this study is the feasibility of introducing suitable species of fish (native and exotic) for rearing in cages in the southern region of the Caspian Sea. This study from the perspective of economic efficiency and maintaining ecology were analyzed. The results showed that the southern Caspian Sea has the ability to aquaculture fish. However, due to the yearly temperature variations of water (from surface to a depth of 50 meters), the talent of aquaculture area is preferred for fish in cold water than warm water fish due to possibility rearing over the years. The survey showed that the current conditions and due to unfavorable changes in the ecology of the area in the last decade, the use of non-native fish culture in cages is not recommended. Many species of native fish are suitable for rearing in cages. Nevertheless, there is no infrastructure suitable for the production of all of them. Therefore, respectively species of Salmo caspius, Huso huso and Common carp of Caspian Sea for cultivation of in cages was suggested. In the current situation, this fish for their ability to grow faster than the need for selectivity. It is noteworthy that detailed environmental assessments and species risk assessments before the final introduction of any fish species (native and exotic) for rearing in cages in the Caspian Sea ecosystem is essential