Introduction Pond fish farming is a primary sector of aquaculture established in Iraq, in conjunction with fish farming in floating cages and recirculating systems. Aquaculture development in Iraq commenced in 1956 with the introduction of cultured species, including carp, tilapia, and rainbow trout, at the Al-Zafarania fish farm. Consequently, both public and private aquaculture facilities appeared across several provinces of Iraq, with the number of farms fluctuating between 1 600 and 2 700 at different intervals. The yearly output quantities of pond fish in Iraq have consistently risen: from 1980 to 2000, production remained below 2-4 thousand tons, however from 2005 to 2019, it escalated to 17-21 thousand tons. The aquaculture system in earthen ponds use semi-intensive polyculture technology. The predominant species farmed in pond aquaculture are common carp (Cyprinus carpio), silver carp (Hypophthalmichthys molitrix), and grass carp (Ctenopharyngodon idella) [1].Investigations into the aquaculture system in earthen ponds in Iraq concentrate on examining the present condition and future potential of pond fish farming in designated provinces [2], the efficacy of common carp cultivation within and outside cages situated in earthen ponds [3], the aquaculture practices and biological metrics of diverse carp groups [4], and the impact of various feed types on the growth rate and survival of carp larvae [5].The progress of technology for cultivating common carp fingerlings is crucial for the future expansion of pond aquaculture in Iraq; nevertheless, the efficacy of rearing carp juveniles of different sizes has not been extensively investigated. This study aims to evaluate the efficacy of raising common carp juveniles from an initial weight of 10 grams to the fingerling stage in earthen ponds, utilizing pellet feed, in central Iraq.  Materials and methods of research The research was  carried  out  in  the  Central  Fish Hatchery in Al-Suwayrah, Wasit Province, Republic of Iraq, from July to October 2023. The hatchery, constructed by a Hungarian firm in the 1980s, has fish breeding ponds, a production laboratory, and administrative facilities. The research focused on one-month-old common carp (Cyprinus carpio) fingerlings, averaging 10 g in body weight. A total of 2 100 fingerlings were allocated across three ponds, with 700 individuals in each pond. The fingerlings were cultivated in earthen ponds covering an area of 2 000 m². To improve the natural food substrate, organic fertilizers (cattle dung at 400 kg/ha) were utilized before to the commencement of raising. The ponds were initially filled with freshwater from the Tigris River to a level of 0.2 m, which was subsequently elevated to 1 m after a duration of 10 days. The physicochemical properties of the water were assessed everyday. The health of the fish was monitored via visual evaluation of their look and activity. All operations were conducted in compliance with international regulations for the management of experimental animals, ensuring the reduction of stress and suffering in the fish [6]. Temperature, dissolved oxygen, transparency, pH, electrical conductivity, total alkalinity, and total hardness of pond water determined daily were measured daily in the field using the Multiparameter Water Quality Meter (Pro Plus, YSI Inc., USA), equipped with high-precision sensors for rapid and accurate readings. Water samples for laboratory analysis were collected in acid-washed polyethylene bottles, filtered through glass fiber filters (0.45 microns) and stored at a temperature of <10 °C before shipment. Concentration of ions (phosphates, nitrates, nitrites, ammonium) were analyzed using standard spectrophotometric methods according to APHA (American Public Health Association) guidelines. The average monthly values of physicochemical indicators corresponded to the regulatory requirements for carp (Table 1). Table 1Physico-chemical indicators of pond water qualityIndicatorJulyAugustSeptemberOctoberTemperature, °C31.2 ± 1.1330.9 ± 1.4329.4 ± 1.3228.3 ± 1.5Dissolved oxygen, mg/l6.5 ± 0.266.7 ± 0,36.3 ± 0.436.1 ± 0.41Water transparency, cm13.4 ± 1.1211.0 ± 1.4213.0 ± 1.2011.5 ± 1.35pH7.37 ± 0.497.24 ± 0.427.8 ± 0.417.53 ± 0.89Electric conductivity, mS/cm0.952 ± 0.201.203 ± 0.211.543 ± 0.381.754 ± 0.38Total alkalinity, mg/l190.0 ± 61.0267.0 ± 64.0260.0 ± 70.0376.0 ± 77.0Total hardness, mg/l188.0 ± 92.20230.0 ± 85.59384.0 ± 80.12409.0 ± 94.3Phosphate concentration, mg/l0.09 ± 0.040.07 ± 0.060.08 ± 0.030.19 ± 0.08Nitrate concentration, mg/l0.73 ± 0.491.04 ± 0.321.16 ± 0.021.46 ± 0.06Nitrite concentration, mg/l0.27 ± 0.100.31 ± 0.110.3 ± 0.160.09 ± 0.12Ammonium concentration, mg/l0.04 ± 0.010.06 ± 0.010.02 ± 0.050.03 ± 0.03  Phytoplankton abundance was determined in water samples with a volume of 1 liter, which were treated with a 1% Lugol solution and examined under a microscope to identify and count species. The monthly average values of phytoplankton abundance in July and October were small, but increased in August and especially in September, with the pronounced dominance of Chlorophyta and Cyanobacteria groups (Table 2). Table 2The average monthly abundance of phytoplankton of various groups in ponds, ×104 individuals/lPhytoplankton groupsJulyAugustSeptemberOctoberCyanobacterium34.9 ± 4.3207.7 ± 2.5900.0 ± 10.027.6 ± 0.2Chlorophyta18.8 ± 0.5320.7 ± 9.01 630.0 ± 30.012.5 ± 12.5Bacillariophyta10.3 ± 1.125.5 ± 0.3314.7 ± 4.215.3 ± 0.1Euglenophyta12.0 ± 0.6141.3 ± 1.5147.3 ± 1.615.5 ± 15.5Pyrrhophyta10.0 ± 0.2123.7 ± 3.5353.3 ± 15.36.4 ± 6.4Chrysophyta12.5 ± 0.627.2 ± 1.1334.4 ± 14.512.1 ± 12.1Pennales10.5 ± 0.619.2 ± 0.4283.0 ± 4.411.5 ± 11.5  Zooplankton abundance was determined by filtering 30 liters of water through a plankton network with a mesh size of 50 microns, fixing the sample in a 4% formalin solution and examining it under a microscope. The average monthly zooplankton abundance was minimal in July and maximal in August, with the Rotifers group dominating (Table 3).  Table 3The average monthly abundance of zooplankton of various groups in ponds, ×104 individuals/lZooplankton groupsJulyAugustSeptemberOctoberRotifers58.7 ± 8.1206.7 ± 10.7115.0 ± 5.0113.3 ± 15.3Copepoda8.6 ± 1.237.0 ± 2.054.2 ± 2.754.1 ± 2.9Cladocera10.8 ± 3.331.7 ± 4.722.0 ± 4.612.7 ± 3.5Daphniidae12.3 ± 5.915.0 ± 3.611.5 ± 3.916.0 ± 3.6Others25.0 ± 2.0110.0 ± 10.031.7 ± 5.019.0 ± 9.5  Feeding was performed twice a day using granular feed. The daily feeding ration was 5% of the fish biomass. The food contained fishmeal, soy meal, corn flour, rice bran, vegetable oil “Vizavit” and mineral and vitamin premix. The feed contained 32% crude protein and 18 megajoules of metabolic energy (Table 4). Table 4The content of nutrients and energy in the feedIndicatorParameterDry matter, %90.4Crude protein, %32.0Crude fat, %4.5Crude fiber, %6.5Ash, %10.6Exchangeable energy, MJ/kg feed18.0 Morphological studies of juvenile common carp were carried out in accordance with the methodological recommendations developed by I. F. Pravdin [7]. Fish for measurements were caught after a partial decrease in the water level in the pond in the early morning to reduce its stress. The caught fish were placed in plastic containers with water from the same pond. After taking measurements, the fish were carefully returned to the pond. The mass and total body length of the juveniles were recorded at the beginning of the experiment, then every 21 days and at the end of the growing period. Measurements were carried out on a sample of at least 100 fish. Body weight was measured with an accuracy of 0.01 g using electronic scales, and body length with a caliper with an accuracy of 0.1 cm. Body weight gain and feed conversion rate (FCR) were determined bya generally accepted method. The costs associated with the cultivation of juvenile carp were estimated in accordance with the following articles: – costs of fixed assets (depreciation and maintenance of ponds, equipment and transport); – costs of working capital (fish planting material for stocking, feed, water resources, electricity, fuel, fertilizers); – the cost of the wage fund (remuneration of personnel engaged in the cultivation, feeding and maintenance of ponds.; deductions for social needs); – overhead costs (administrative, utility).  Research resultsThe number of juvenile carp decreased significantly during the first three weeks of cultivation: from 700 at the beginning to 615-628 specimens per pond at the end of the stage (Table 5).  Table 5Dynamics of the number of juvenile carp in ponds, specimensReplicateWhen stockingDuration of cultivation, days21426390Pond R1700628616606605Pond R2615614610602Pond R3619609605604  The number of juveniles at the next stages of cultivation changed little, amounting to 602-605 specimens per pond by the 90th day of cultivation. As a result, the safety of juveniles during the first stage of cultivation turned out to be the lowest – 88.67 ± 0.55%. The preservation rate at the next stages of juvenile cultivation was stable in the range from 98.77 to 99.45%. The safety of fish for the entire time of cultivation was86.24 ± 0.13%. The obtained parameters are consistent with the data of earlier studies, which confirm the high survival rate of carp with proper management of the reservoir [8, 9].The body weight of the cultured carp juveniles exhibited a consistent growth during all cultivation periods (Table 6).  Table 6Dynamics of body weight of juvenile carp, gramsReplicateWhen stockingDuration of cultivation, days21426390Pond R19.96 ± 0.8946.25 ± 4.0090.12 ± 6.36184.75 ± 9.40270.45 ± 11.3Pond R210.01 ± 0.4950.27 ± 3.8489.37 ± 7.30173.04 ± 9.38257.07 ± 11.8Pond R310.00 ± 0.7050.25 ± 5.3294.44 ± 7.83187.61 ± 9.89274.36 ± 12.4  On the 90th day of cultivation, the average body weight of juveniles in ponds ranged from 257.07 to 274.36 grams, showing no significant differences between replicas. The individual body weight gain of juveniles over the entire growing period was in the range from 247.06 to 264.36 grams. The average body weight of the grown juveniles on the 90th day of cultivation was 267.29 ± 5.23 grams. Thus, the value of this indicator increased by 26.76 times during cultivation. There is no doubt that the intensive growth of juveniles in ponds largely depends on additional feeding, as indicated by other authors [10].The total body length of juveniles gradually increased during the growing period from 7.03-7.14 cm initially to 24.82-24.85 cm (Table 7).  Table 7Dynamics of total body length of juvenile carp, cmReplicateWhen stockingDuration of cultivation, days21426390Pond R17.13 ± 0.8914.04 ± 1.0015.89 ± 1.4521.08 ± 1.6724.85 ± 1.89Pond R27.14 ± 0.4914.03 ± 1.2415.84 ± 1.4621.09 ± 1.6824.82 ± 1.90Pond R37.14 ± 0.7013.97 ± 1.2515.82 ± 1.4721.06 ± 1.6924.83 ± 1.91 The absolute increase in total body length over 90 days was 17.68-17.72 cm. The average value of the total body length of juvenile carp at the end of cultivation was 24.83 ± 0.01 cm.The fatness coefficient of juveniles at the stages of cultivation fluctuated in waves, which can be explained by the uneven linear growth of fish in different directions (Table 8).  Table 8Dynamics of the fatness coefficient of juvenile carp, unitsReplicateWhen stockingDuration of cultivation, days21426390Pond R12.75 ± 0.101.67 ± 0.082.25 ± 0.121.97 ± 0.101.76 ± 0.09Pond R21.82 ± 0.092.25 ± 0.131.85 ± 0.091.68 ± 0.08Pond R31.84 ± 0.092.39 ± 0.132.01 ± 0.101.79 ± 0.09  The value of the fatness coefficient at the end of cultivation turned out to be in the range from 1.68 to 1.79, which indicates a good fatness of the fish planting material. The average value of the fatness coefficient of carp juveniles by the 90th day of cultivation turned out to be 1.75 ± 0.03.The total biomass of juvenile carp steadily increased from the initial 6.97-7.01 kg per pond to 154.76-165.71 kg per pond at the end. The total increase in biomass over 90 days ranged from 147.75 to 158.71 kg per pond (Table 9).  Table 9Dynamics of the biomass of juvenile carp, kg per pondReplicateWhen stockingDuration of cultivation, days21426390Pond R16.9729.0555.51111.96163.63Pond R27.0130.9154.87105.55154.76Pond R37.0031.1157.51113.51165.71  The average biomass value of the grown juveniles on the 90th day of cultivation was 161.36 ± 3.36 kg per pond. As a result, the value of the analyzed indicator increased by 23.08 times during cultivation.The fish productivity of ponds gradually increased during the growing of juvenile carp, reaching the level of 738.75-793.57 kg/ha after 90 days (Table 10).  Table 10Dynamics of fish productivity of ponds during the cultivation of juvenile carp, kg/haReplicateDuration of cultivation, days21426390Pond R1110.37242.71524.93783.25Pond R2119.55239.33492.74738.75Pond R3120.52252.57532.52793.57  The average value of fish productivity of ponds for 90 days of growing juvenile carp was 771.85 ± 16.82 kg/ha. The results of the study indicate a steady increase in fish productivity of ponds during the cultivation of juvenile carp.Feed consumption at the first stage of cultivation turned out to be in the range of 25.24-27.65 kg per pond, but later it increased significantly. Feed consumption for 90 days of cultivation was 300.09 ± 3.56 kg per pond with fluctuations from 295.81 to 307.16 (Table 11). Table 11Dynamics of feed consumption during rearing of carp juveniles in ponds, kg per pondReplicateGrowing stage, daysfirst (from the 1stto the 21stsecond (from the 22nd to the 42nd)third (from the 43rd  to the 63rd)fourth (from the 64th to the 90th)for all the time (from the1st to the 90th)Pond R127.6546.3192.05131.29297.30Pond R225.2947.7796.54137.56307.16Pond R325.2444.5592.67133.35295.81 The maximum conversion of feed into biomass growth of juvenile carp was observed at the first stage of cultivation, when the average FCR value was 1.12 ± 0.07 with variability ranging from 1.05 to 1.25 (Table 12).  Table 12Dynamics of the feed conversion ratio during the cultivation of juvenile carp, unitsReplicateGrowing stage, daysfirst (from the1st to the 21stsecond (from the 22nd to the 42nd)third (from the 43rd to the 63rd)fourth (from the 64th to the 90th)for all the time (from the1st to the 90th)Pond R11.251.751.632.541.90Pond R21.061.991.902.802.08Pond R31.051.691.662.551.86  At the next stages of cultivation, an increase in this indicator was noted to 1.81 ± 0.09 (second), 1.73 ± 0.09 (third) and 2.63 ± 0.08 (fourth). The feed conversion rate for 90 days of growing juvenile carp was1.95 ± 0.07 with fluctuations in the range from 1.86 to 2.08. The value of the feed conversion rate is an important parameter in the cultivation of juvenile carp, having a strong impact on its cost.The total biomass of juvenile carp after 90 days of  cultivation was 484.1 kg. Total costs of fish farming was 125,638.61 Russian rubles (RUB) or 2,062,985.98 Iraqi dinars (IQD). Costs of growing 1 hundredweight of juvenile carp was 25,953.03 RUB or 426,148.75 IQD. The share of expenses on working capital and depreciation of fixed assets turned out to be the most significant in the structure of production costs: 55.75 and 20.21%, respectively (Table 13). Table 13Cost structure of growing young carpCost itemTotal costs, RUBCosts for 1 hundredweightof grown juveniles, RUBShare of costs in the cost price of reared calves, %Fixed assets25,403.035,247.4820.22Working assets70,053.7614,470.9355.76Wages fund15,719.703,247.2012.51Overhead costs14,462.122,987.4211.51Total125,638.6125,953.03100.00  ConclusionAn assessment of the effectiveness of growing juvenile common carp with an initial weight of 10 grams in the environmental conditions of groundwater ponds in the Central part of Iraq showed a high level of preservation for 90 days – 86.24 ± 0.13%. At the end of adulthood, juveniles reach a body weight of 257.07-274.36 grams and a total length of 24.8-24.9 cm. Intensive growth of juveniles makes it possible to obtain a high level of fish productivity in ponds in 90 days – 771.85 ± 16.82 kg/ha. Most of costs of growing juvenile carp in ground ponds are accounted for by the use of working capital (55.75%) and depreciation of fixed assets (20.21%). The cost of the grown carp planting material is 25,953.03 Russian rubles or 426,148.75 Iraqi dinars per one hundredweight of products, which indicates its competitiveness. The results of the study of fish farming, biological and economic indicators of the cultivation of juvenile carp with an initial weight of 10 grams in ground ponds are of great importance for the production of carp planting material in Iraq.