Technological approaches to grow-out: a comparative study of pikeperch (Sander lucioperca) culture in three different production systems during the growing season

Technological approaches to grow-out: a comparative study of pikeperch (Sander lucioperca) culture in three different production systems during the growing season Va ´clav Kuc ˇera*, Toma ´s ˇPe ˇnka, Oleksandr Malinovskyi, Jitka Kola ´r ˇova ´,Ja ´n Regenda and Toma ´s ˇPolicar Faculty of Fisheries and Protection of Waters, University of South Bohemia in C ˇ eske ´Bude ˇjovice, South Bohemian Research Centre of Aquaculture and Biodiversity of Hydrocenoses, Vodn ˇany, Czechia This study compares pikeperch (Sander lucioperca) production in three systems: a recirculating aquaculture system (RAS), an in-pond raceway system (IPRS), and a traditional pond polyculture (POND). Each system was stocked with 1500 juveniles and cultured for 24 weeks. The RAS fish exhibited the most intensive growth, achieving the highest final total length, final body weight, condition factor and specific growth rate, alongside the lowest food conversion ratio (FCR). However, the increased hepatosomatic index, intraperitoneal fat and ammonia levels suggested an increased metabolism. Notably, RAS fish displayed the highest frequency of fin erosion, particularly in the caudal and first and second dorsal fins. The IPRS group exhibited slower growth, higher FCR and higher plasma glucose levels than the other groups. IPRS fish also showed fin erosion in caudal and both pectoral fins. RAS and IPRS fish demonstrated similar survival rates. Conversely, the POND group exhibited significantly lower survival, likely because of adaptability and water quality issues. Blood plasma analysis of POND fish indicated starvation, marked by elevated alanine aminotransferase and lipase levels, supported by non-existing fat reserves. In summary, RAS yielded the best growth and feed efficiency, although it was associated with increased metabolic stress and fin erosion. IPRS showed slower growth but proved cost-effective during the growing season. Traditional pond culture was unsuccessful owing to adaptability in and the water quality of ponds. An economic evaluation revealed that production costs per pikeperch juvenile were significantly lower in the IPRS compared with that in the RAS, thereby compensating for slower growth. KEYWORDS pikeperch, production, intensification, rearing technology, physiological status, mortality Frontiers in Marine Science frontiersin.org01 OPEN ACCESS EDITED BY Luca Parma, University of Bologna, Italy REVIEWED BY Stefan Reiser, Thuenen Institut Braunschweig, Germany Amit Ranjan, Tamil Nadu Fisheries University, India *CORRESPONDENCE Va ´clav Kuc ˇera [email protected] RECEIVED 17 February 2025 ACCEPTED 09 May 2025 PUBLISHED 02 June 2025 CORRECTED 22 October 2025 CITATION Kuc ˇera V, Pe ˇnka T, Malinovskyi O, Kola ´r ˇova ´J, Regenda J and Policar T (2025) Technological approaches to grow-out: a comparative study of pikeperch (Sander lucioperca) culture in three different production systems during the growing season. Front. Mar. Sci. 12:1578274. doi: 10.3389/fmars.2025.1578274 COPYRIGHT ©2025Kuc ˇera, Pe ˇnka, Malinovskyi, Kola ´r ˇova ´, Regenda and Policar. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. TYPE Original Research PUBLISHED 02 June 2025 DOI 10.3389/fmars.2025.1578274 1 Introduction European inland aquaculture has chosen diversification as a tool to increase production (Baekelandt et al., 2018). Pikeperch was selected among other species for intensive aquaculture (Policar et al., 2019) given its high value, rapid growth and good flesh quality. Owing to these traits, pikeperch production in aquaculture is constantly increasing. Conversely, production from open waters has gradually decreased over the years, dropping to ~50% since 1950 (FAO, 2022). This creates an opportunity for farmers to further increase their production to fill the market gap. In Western Europe, such as Belgium and France, insufficient pond farming area forces farmers to produce pikeperch in closed aquaculture systems (RAS). Thereafter, controlled pikeperch aquaculture was highly industrialised, which led to high costs of initial investment and maintenance (Overton et al., 2015). Numerous studies have focused on the optimisation of broodstock management (Malinovskyi et al., 2018, 2019), reproduction (Samarin et al., 2016;Kristan et al., 2018), juvenile and on-growing feeding (Kowalska et al., 2015;Penka et al., 2023;Schulz et al., 2007), light regimes (Luchiari et al., 2006), stocking densities (Ljubobratovicet al., 2016;Kozłowski and Piotrowska, 2023), biculture stockings (Penka et al., 2021, 2024)anduseoflivefeedforlarvalculture(Imentai et al., 2019; Yanes-Roca et al., 2018;2020) to further ensure the feasibility of RAS operation. In recent years, a drastic rise in energy costs has decreased the profitability of pikeperch intensive farms, prompting the need for less energy demanding production methods. Extensive or semi-intensive pond culture remains the least expensive option for fish production, but the seasonal nature of fish supply, low species diversity and increasing temperatures, which cause algae blooms and oxygen deficiencies, make pond culture unpredictable and less efficient. Nevertheless, in CEER countries (Central East European countries—Czech Republic, Poland,Hungary,Austria,SlovakiaandGermany),themajority of farmed pikeperch (FAO, 2022), as well as the overall share of aquaculture production of up to 80%–88% (Vavrecka et al., 2019), originates from ponds. The existing pond infrastructure in the combination with new technological equipment provides an opportunity to increase the production capacity of ponds. One of the production possibilities were the cages that were used for controlled fish production in Central Europe during the 20 th century were partially successful. However, cages have the disadvantages of insufficient water circulation, which is directly related to decreased water quality and low oxygen levels (Brune et al., 2003). The in-pond raceway system (IPRS) provides better water quality, is easy to install in existing ponds and provides better water circulation and aeration while using an air lift as a power medium (Masser, 2012). IPRS has been used in only two published studies on pikeperch culture regarding broodstock management (Ljubobratovicet al., 2019)andthegrow-out phase of juveniles (Nagy et al., 2022). The study by Nagy et al. (2022) suggests that pikeperch rearing is compatible with IPRS and should be further examined and economically evaluated. Herein, the advantages and disadvantages of traditional fish farming in ponds, modern fish farming using RAS and the hybrid system of IPRS, which combines both approaches to fish culture, are evaluated. 2 Materials and methods 2.1 Place and duration of the experiment The experiment was conducted in the large scale-experimental RAS and IPRS at the Laboratory of Intensive Aquaculture, Faculty of Fisheries and Protection of Waters, University of South Bohemia in CeskeBudejovice, Czechia and in three experimental ponds belonging to the Experimental Fish Culture Facility of the same faculty as the previous production systems. The duration of the experiment was 168 days (24 weeks) during the growing season, starting on April 11 th and finishing on September 26 th . 2.2 Production systems 2.2.1 RAS For this study, a semi-experimental RAS comprising 10 cylindrical tanks, each with a volume of 1.5 m³, was used (Figure 1). The bottom outflow of the tank was connected directly to a drum mechanical filter 1-FB (IN-EKO Team, Tisnov, Czech Republic) with a flow rate of 28– 000 L.h −1 and to a moving bed biofiltration unit with a volume of 14.6 m³ powered by two air-pumps (Secoh El-S-250; 250 L.min −1 ,Secoh Ltd., Shanghai). After the sterilisation process using an ozone generator OT 10 model (Ozontech s.r.o., Zlın, Czech Republic) with the dose of 10 g per hour and 6 hour application (Kolarovaet al., 2021)and saturation with pure oxygen, water was run from the distribution tank gravitationally back into the rearing tanks. The water flow in the tanks was set at an exchange rate of twice per hour for consistent oxygen saturation and efficient faeces discard. 2.2.2 IPRS The IPRS comprised nine separate floating plastic tanks (Figure 2). Each tank had a volume of 7.2 m³ (4 × 1.5 × 1.2 m) and was fitted with two stainless steel grated openings on opposite sides. The first grated openingwas located directly under the water surface and provided top inflow. The second grated opening was located at the bottom and enabled the disposal of uneaten feed, faeces and other debris from the tanks into the pond. The water inflow was provided by an airlift located in the siphon under the inlet opening. The airlift through the siphon produced large bubbles of air, creating a slow water current that carried water to the surface. This current provided continuous water exchange inside the rearing tanks while also bringing fresh oxygen-rich water. The IPRS was powered by an air-pump Kubıcek 3D19S-051E (940 L.min −1 , Kubıcek VHS s.r.o., Czech Republic). The open top of the tanks was covered with a net to protect the fish from predators and falling debris. The pond used for this floating system had a total area of 0.3 hectare with an average depth of 1.8 m and was filled by a water from the Blanice River. Kuc ˇera et al. 10.3389/fmars.2025.1578274 Frontiers in Marine Science frontiersin.org02 2.2.3 POND In this experiment, three identical experimental ponds were used by the POND group. Each pond had a total area of 0.1 ha with an average depth of 1 m (Figure 3). The ponds were filled by the same water channel from the Blanice River as the pond where IPRS was situated. The bottom inflow was fitted with a fine mesh bag to prevent fishfrom the river from entering the pond. The outflow was fitted with fine bars to prevent the fish from escaping from the pond. 2.3 Experimental groups and feeding In each rearing system (RAS, IPRS and POND), pikeperch juveniles with a mean initial body weight (IBW) of 51.6 ± 10.33 g were stocked. Each rearing system was stocked in triplicate with 500 individuals per repetition (a total of 1500 juveniles per group, 4500 juveniles in total). Pikeperch was stocked into each rearing system 2 weeks before the start of the experiment to ensure the fish adapted to the new environment. All juvenile pikeperch originated from a RAS–POND combination production system, according to Policar et al. (2016). These juveniles were initially fed floating feed, Skretting Europa-15F (55% protein, 16% fat, 10% fibre, 0.7% ash, 1.5% phosphorus, 19.4 MJ.kg −1 digestible energy, size 2–3 mm), which was subsequently provided to the fish during the IPRS and RAS trials. Feed was distributed into the RAS and IPRS tanks using belt feeders for >8 h per day. Depending on the water temperature, oxygen levels and appetite of the fish, the daily feeding ratio (DFR) oscillated from 0.3% to 1.5% of biomass per day. The mean initial FIGURE 1 Large-scale experimental RAS of LIA FFPW USB in Vodnany (V. Kucera). FIGURE 2 IPRS of LIA, FFPW USB Vodnany consisting of 9 tanks, 7.2m 3 each (V. Kucera). Kuc ˇera et al. 10.3389/fmars.2025.1578274 Frontiers in Marine Science frontiersin.org03 biomasses were established as follows: 17.2 kg.m −1 (RAS) and 3.58 kg.m −3 (IPRS), depending on the culture intensity level. Both systems operated under a stock monoculture regime. In POND conditions, 258 kg.ha −1 of pikeperch were stocked. To help imitate the conditions of extensive pond culture in Central Europe, the following fish species were added to the polyculture in the following biomasses: common carp (Cyprinus carpio), 168 kg.ha −1 (177 individuals, IBW 94.3 ± 0.1 g); broodstock of tench (Tinca tinca), 74.5 kg.ha −1 (8 individuals, IBW 896.5 ± 27.4 g) and broodstock of rudd (Scardinius erythropthalamus), 101.5 kg.ha −1 (60 individuals, IBW 171.1 ± 0.9 g). The broodstock of tench and rudd was added to provide prey fish for pikeperch via natural spawning. 2.4 Abiotic conditions IntheRASandIPRSenvironments,watertemperatureandoxygen levels were measured daily at 7:00 using a YSI ProODO oximeter (YSI Inc., Yellow Springs, OH, USA). The pH was measured once a day at 7:00 am using a WTW 3310 pH-metre (WTW, Prague, Czech Republic). Total ammonia and nitrite levels were determined daily at 7:30 am using simple titration and colourimetry reference kits, according to Penka et al. (2021). All the previously mentioned abiotic conditions in the ponds were measured thrice a week using the same equipment, and sampling was performed at the same time as in the RAS and IPRS. All water quality parameters in each production system are summarised in Table 1. 2.5 Evaluated production parameters Atthebeginningoftheexperiment,100individualsweresubjected to biometric measurements (body weight [BW], total length [TL] and standard length [SL]) using a measuring board and digital scale (KERN KB 2400-2N; Kern & Sohn, GmbH, Germany). Fin erosion was determined in 90 individuals, following Policar et al. (2016).Before manipulation, fish were anaesthetised using clove oil (0.04 ml. l −1 ) (Kristan et al., 2014). Blood was collected from 12 individuals from the vena caudalis using a heparinised needle (5000 IU/ml, Leciva, Prague, Czech Republic) and a syringe. After plasma centrifugal separation, the samples were stored at −80°C until biochemical analysis. The following biochemical parameters in blood plasma were analysed: total protein (TP), albumin (ALB), globulin (GLB), amylase (AMYL), lipase (LIPA), total cholesterol (TCHOL), glucose (GLU), ammonia (NH 3 ), triglyceride (TAG), alanine aminotransferase (ALP) and aspartate aminotransferase (AST). The measurement was made using the biochemical analyser FUJI DRI-CHEM NX 500i (FUJIFILM Europe GmbH, Dusseldorf, Germany). After blood sampling, fish were euthanised and dissected to determine the weight of individual internal organs for the calculation of somatic indices such as hepatosomatic index (HSI), intraperitoneal fat index (IPFI), spleensomatic index (SSI), gonadosomatic index (GSI) and relative gut length (RGL). Dissections were performed under veterinary guidance, supported by good practice. During the experiment, the mortality of the cultured fish was checked daily, and all deceased individuals were counted and recorded to calculate the survival rate (SR). For the exact calculation of the feed conversion ratio (FCR), uneaten feed was checked daily during the feeding of the fish and maintenance of the rearing tanks. TABLE 1 Abiotic conditions in all production systems during the experiment. Parameter RAS IPRS POND O 2 (%) 131 ± 14.5 92.1 ± 16.6 90.5 ± 27.9 NO 2- (mg. L - ¹) 0.67 ± 0.31 0.26 ± 0.14 0.35 ± 0.10 NH 4+ (mg. L -1 ) 0.68 ± 0.30 0.53 ± 0.28 0.42 ± 0.11 pH 6.86 ± 0.21 7.16 ± 0.26 7.89 ± 0.92 T(˚C) 21.9 ± 2.64 17.0 ± 4.07 18.4 ± 4.24 FIGURE 3 Experimental ponds with acreage of 0.1 ha and average depth of 1m in Experimental Fish Culture Facility of FFPW USB Vodnany (photo by V. Kucera). Kuc ˇera et al. 10.3389/fmars.2025.1578274 Frontiers in Marine Science frontiersin.org04 At the end of the experiment, 300 individuals from each group were subjected to biometric measurements (BW, SL and TL) using the same technological equipment used at the beginning of the trial. The erosion of fins was assessed in 90 individuals from each group described above. The state of erosion was assessed by qualified personnel and divided into four categories (0–4), and their percentage distribution was calculated for each group according to (Policar et al., 2016). Blood samples were drawn from 12 individuals from each experimental group (36 fish in total), and these fish were, as at the beginning, dissected for internal organ inspection and subsequent determination of somatic indices. The following production parameters were calculated according to the following formulas from the determined BW, TL and SL: number of surviving fish, consumed feed, number of days of trial and weight of dissected organs at the both beginning and termination of the trial: The specificgrowthrate(SGR)(%.d −1 ) was calculated as follows: SGR=ln FBW −ln IBW tx100 SR (%) was calculated as follows: SR =  NF NI x100 Weight gain (%) was calculated as follows: WG = ( FBW IBW x100) −100 The feed conversion ratio (g. g - ¹) was calculated as follows: FCR = F BG The condition factors were calculated as follows: CF=BW TL3100 The hepatosomatic index (%) was calculated as follows: HSI =WL BW x 100 The IPFI (%) was calculated as follows: IPFI =WIPF BW x 100 The spleensomatic index (%) was calculated as follows: SSI =WS BW x 100 The gonadosomatic index (%) was calculated as follows: GSI =WG BW x 100 The RGL was calculated as follows: RGL =GL SL In all the formulas, the following measurements and records were used: initial and final body weight (IBW and FBW), final total length (FTL), number of days of the trial (t), number of fish in the sample (N), final number of fish (NF), initial number of fish (NI), feed consumption (F), biomass gain (BG), total length (TL), standard length (SL), body weight (BW), weight of the liver (WL), weight of IPFI (WIPF), weight of spleen (WS), weight of gonad (WG) and gut length (GL). 2.6 Economic evaluation To calculate production costs for pikeperch juveniles, the following cost categories were evaluated: feed, electricity, tap water, oxygen, personnel (including insurance and tax), stocking material, chemicals and depreciation costs. The final production cost was compared with the final number of produced fish to calculate the exact production cost per fish. Personal cost was calculatedonthebasisofthetimespentworkingwitheach system.IncaseofthreetanksinRASitwasonaverage60 minutes per day. In case of IPRS it was 45 minutes per day. In case of the POND price of personell was calculated to cover the personal cost during the harvest, sorting the fish after harvest and occasional work like cleaning the ouflow and inflow of the ponds during growing season. To estimate the production cost of pikeperch in a polyculture system, personal labor, electricity, and depreciation expenses were evenly allocated among the cultured fish species (common carp, pikeperch, rudd, and tench broodstock), with each group assigned 25% of the total operational costs, excluding those related to stocking material. Although pikeperch accounted for only 2.38% of the total harvested biomass at the termination of the experiment, this imbalance was offset by its disproportionately higher share at the beginning of the production cycle, when pikeperch represented 42.3% of the total stocked biomass due to the more complex and demanding nature of its stocking process.All the time spend on data collection, sampling, calculating of uneaten feed etc was not included as it does not reflect a standard production practices and it would artificially increase production cost of the fish in this study 2.7 Statistical analyses Data were analysed using the Rstudio software (R Core Team, 2014). Before the statistical analysis, several preliminary tests were conducted. The Shapiro–Wilk test was used to determine the normality of the residuals, whereas Levene’s test was employed to inspect the homogeneity of variance. Furthermore, the Kolmogorov–Smirnov test was used to assess data normality. The production parameters were compared using one-way ANOVA, with a significance margin set at P < 0.05. The homogeneity of the data was assessed using the Tukey’s Honestly Significant Difference method. All data are presented as the mean ± standard deviation (SD). Kuc ˇera et al. 10.3389/fmars.2025.1578274 Frontiers in Marine Science frontiersin.org05 3 Results 3.1 Growth and feed utilisation of the pikeperch Pikeperch juveniles cultured in different rearing systems achieved significantly different growth rates. The highest FBW was 190.0 ± 67.72 g (RAS, almost quadrupled their BW during the experiment) compared with 121.0 ± 36.39 g (IPRS, more than doubled their BW during the experiment), and the lowest FBW was 62.5 ± 19.26 g in the POND group, which was fully correlating with the FTL of 278.6 ± 32.5, 249 ± 23.20 and 208 ± 15.76 mm, respectively. The same trend was observed in weight gain, which was the highest (268.0% ± 21.23%) in the RAS, 132.7% ± 1.25% in the IPRS and the lowest (28.3% ± 18.56%) in POND. FCR reached 1.0 ± 0.03 and 1.6 ± 0.10 in the RAS and IPRS, respectively. In terms of SGR, this result corresponds to the highest value (0.7 ± 0.01%.day −1 ) in the RAS, 0.4 ± 0.02%.day −1 in the IPRS, and the lowest value (0.1 ± 0.08%.day −1 ) in the POND group. Regarding CF, fish from the RAS had the highest CF value of 1.3 ± 0.10 compared with 1.2 ± 0.11 in the IPRS and 1.1 ± 0.17 in the POND group. The total mean BG in the RAS was 53,120 g, whereas it was 26,208 g in the IPRS. In the ponds, no gain in biomass was observed owing to the low SR of pikeperch juveniles. All mentioned production data are presented in Table 2. 3.2 Growth of other fish species in pond polyculture In the polyculture regime of stock in ponds, other fish species also displayed growth. The highest growth rate was observed in common carp, which increased from an IBW of 94.3 g to an FBW of 515.0 ± 75.0 g, resulting in a WG of 446.4% and an SGR of 1.0 ± 0.1%.day −1 . The tench reached an FBW of 908.3 ± 53.6 g from an IBW of 896.5 ± 27.4 g, resulting in a WG of 1% and an SGR of 0.052%.day −1 . The broodstock of rudd reached almost a similar result, growing from an IBW of 171.1 ± 0.9 g to an FBW of 183.7 ± 9.6 g, resulting in a WG of 7.3% and an SGR of 0.042%.day −1 . 3.3 Survival rate The SRs were statistically similar between the RAS and IPRS (83.9% ± 3.65% and 88.9% ± 0.81%, respectively). The SR in the pond was significantly lower (5.9% ± 4.11%). The mean BW of morbid fish in the RAS was 68.9 g, whereas that in the IPRS was 42.2 g. Moreover, the size of morbid fish in the IPRS decreased throughout the trial, as shown in Figure 4,althoughthefish displayed increasing growth and BW. The dynamics of mortality differed between the RAS and IPRS, as shown in Figure 5. The survival rates of other cultured fish in polyculture stock in ponds were as follows: common carp, 70.3% ± 8.3%; tench, 71.8% ± 15.9% and rudd, 64% ± 28.6%. 3.4 Fin erosion of pikeperch During the assessment of fin erosion, only categories 0 (no damage) and 1 (minor damage) were observed. Categories 2,3 and 4 were not found on inspected individuals indicating that the fish suffered from only minor fin erosion. From the 90 assessed individuals in each group, 68.9% ± 12.86% in the RAS, 40.0% ± 7.2% in the IPRS and 27.2% ± 16.5% in the POND group were affected by the fin erosion in category 1. Fish from the RAS group mostly experienced erosion (category 1) of the caudal fin (25.6% ± 3.1%), first dorsal fin (11.3% ± 4.10%) and second dorsal fin (26.7% ± 2.72%). Fish from the IPRS mostly suffered from the erosion of both pectoral fins (8.89% ± 1.54% left; 11.3% ± 1.54% right) and caudal fins (11.1% ± 4.16%). Fish from the POND group exhibited uneven erosion across all fins, with the highest frequency of erosion (category 1) found on the caudal fin (7.8% ± 6.85%), left pectoral fin (9.06% ± 5.50%) and right ventral fin (6.67% ± 7.20%). A detailed description of the erosion of all fins is presented in Table 3. 3.5 Somatic indices of pikeperch Analysis of the somatic indices of cultured pikeperch showed the following: fish from the RAS displayed significantly higher TABLE 2 Production markers of pikeperch juveniles in three different rearing systems after 24 weeks of rearing. Parameter Initial RAS IPRS POND F-statistics P-value FTL (mm) 197 ± 11.6 c 278.6 ± 32.6 a 249 ± 23.2 b 208 ± 15.8 c F(3,784) = 37.2 P < 0.005 FBW (g) 51.6 ± 10.3 c 190.0 ± 67.7 a 121 ± 36.4 b 62.5 ± 19.3 c F(3,784) = 312 P < 0.005 WG (%) –268.0 ± 21.2 a 132 ± 1.25 b 28.3 ± 18.6 c F(2,6) = 109 P < 0.005 SR (%) –83.90 ± 3.65 a 88.9 ± 0.81 a 5.91 ± 4.11 b F(2, 6) = 421 P < 0.005 CF 1.1 ± 0.10 c 1.3 ± 0.10 a 1.2 ± 0.11 b 1.1 ± 0.17 c F(3,784) = 67.5 P < 0.005 SGR (%.d −1 )–0.7 ± 0.01 a 0.4 ± 0.02 b 0.1 ± 0.08 c F(2,6) = 57.0 P < 0.005 FCR (g.g 1 )–1.0 ± 0.03 a 1.6 ± 0.10 b –F(1,4) = 70.9 P < 0.005 FTL, Final total length; FBW, Final body weight; WG, Weight gain; SR, Survival rate; CF, Condition factor; SGR, Specific growth rate; FCR, Feed conversion ratio. Values with different superscripts (a, b, c) differ significantly (p< 0.05). Kuc ˇera et al. 10.3389/fmars.2025.1578274 Frontiers in Marine Science frontiersin.org06 IPFI together with the IPRS compared with POND-raised fish. RAS-raised fish also exhibited significantly enlarged livers (higher HSI) compared with the other groups. Consequently, the spleen (SSI) was significantly smaller in the RAS and larger in the POND group. The RGL of POND-raised fish was significantly higher than that of the RAS and IPRS-raised fish. No statistically significant differences were found in the GSI. All parameters are described in Table 4. 3.6 Biochemical parameters of pikeperch blood The plasma levels of TP, ALB, GLOB, NH 3 and LIPA were within the ranges normally found in pikeperch in good conditions (Kolarovaand Velısek, 2012). TP was statistically higher in fish from the RAS and IPRS compared with that from the POND group. The concentration of ALB differed significantly among all the tested FIGURE 5 Dynamics of mortality in the experimental IPRS and RAS, episodes of bacterial infection in RAS (8.6., 17.6. and 22.6.) and increase of mortality in IPRS due to the water quality in the pond in late summer and increased heterogeneity among the tank stock. FIGURE 4 Mean body weights of deceased individuals during the experiment in IPRS and RAS groups. Kuc ˇera et al. 10.3389/fmars.2025.1578274 Frontiers in Marine Science frontiersin.org07 groups, with the highest levels in the RAS and the lowest in the POND group. GLOB was statistically higher in the RAS compared with the POND group. GLU was statistically the highest in the IPRS and exceeded the values normally determined in pikeperch under good conditions. AMY showed statistically significant differences among all the groups, being the highest in the RAS and the lowest in the POND group. Fish from POND were the only ones not exceeding the normal values of AMY for pikeperch in good conditions. TCHO did not show any statistically significant differences among the groups. LIP was significantly the highest in the POND group. NH 3 was the highest in the RAS but did not exceed the normal values for pikeperch. TG levels in pikeperch across all the groups, including the fish at the start of the test, were higher than the reported normal values for pikeperch. Among the groups, the TGs were statistically lower in the POND group, which only slightly exceeded the values for pikeperch in good conditions. Increased activity of the liver enzyme ALP was higher in fish from the POND group, with ALP levels in the POND group being two times higher than those in the upper range of pikeperch in good conditions. Pikeperch from the IPRS had the highest AST values compared with those from the POND group and RAS. All biochemical parameters are listed in Table 5. 3.7 Economical evaluation The evaluation of each part of the production cost revealed the following. The highest share represents stocking and personnel costs. These categories are closely followed by feed, depreciation TABLE 3 Frequency of fin erosion on juvenile pikeperch reared in different systems. Parameter Initial RAS IPRS POND LP (%) 3.33 ± 2.72 1.10 ± 1.60 8.89 ± 1.54 9.06 ± 5.50 RP (%) 5.56 ± 1.57 1.12 ± 1.54 11.3 ± 1.54 1.12 ± 1.50 LV (%) 0.00 ± 0.00 1.09 ± 1.52 0.00 ± 0.00 1.28 ± 1.81 RV (%) 0.00 ± 0.00 1.10 ± 1.50 2.31 ± 1.52 6.67 ± 7.20 FD (%) 8.89 ± 1.58 11.3 ± 4.10 2.20 ± 1.62 1.28 ± 1.81 SD (%) 17.8 ± 1.62 26.7 ± 2.72 2.22 ± 3.14 0.00 ± 0.00 Ca (%) 16.7 ± 2.72 25.6 ± 3.14 11.1 ± 4.16 7.78 ± 6.85 An (%) 7.78 ± 4.16 1.00 ± 1.58 2.22 ± 3.14 0.00 ± 0.00 LP, Left Pectoral fin; RP, Right Pectoral fin; LV, Left Ventral fin; RV, Right Ventral fin; FD, First Dorsal fin; SD, Second Dorsal fin; Ca, Caudal fin; An, Anal fin TABLE 4 Somatic indexes of experimental pikeperch from different production systems after 24 weeks of rearing. Parameter Initial RAS IPRS POND F-statistics P-value SSI (%) 0.10 ± 0.02 b 0.01 ± 0.03 a 0.04 ± 0.02 ab 0.07 ± 0.06 b F(3,42) = 522 P < 0.005 HSI (%) 1.58 ± 0.21 a 1.34 ± 0.23 a 1.05 ± 0.12 b 0.87 ± 0.37 b F(3,42) = 51.6 P < 0.005 IPF (%) 3.23 ± 1.06 a 3.61 ± 0.91 a 3.12 ± 0.66 a 0.07 ± 0.18 b F(3,42) = 50.2 P < 0.005 GSI (%) 0.34 ± 0.18 0.52 ± 0.42 0.70 ± 0.73 0.54 ± 0.60 F(3,42) = 0.76 P = 0.524 RGL 0.47 ± 0.08 c 0.67 ± 0.10 b 0.69 ± 0.10 b 0.80 ± 0.10 a F(3,42) = 155 P < 0.005 SSI, Spleensomatic index; HSI, Hepatosomatic index; IPFI, Intraperitoneal fat index; GSI, Gonadosomatic index; RGL, Relative gut length. Values with different superscripts (a, b, c) differ significantly (p< 0.05). TABLE 5 Biochemical parameters of the blood of pikeperch juveniles. Parameter Initial RAS IPRS POND F-statistics P-Value TP (g.L −1 ) 34.7 ± 2.06 a 37.3 ± 5.56 a 32.4 ± 2.97 a 24.8 ± 9.15 b F (3,42) = 6.56 P < 0.005 ALB (g.L −1 ) 3.90 ± 1.52 c 8.33 ± 1.87 a 5.92 ± 1.16 b 2.83 ± 2.17 c F (3.42) = 18.3 P < 0.005 GLU (mmol.L −1 ) 4.99 ± 1.83 c 11.8 ± 4.12 b 20.5 ± 6.51 a 9.47 ± 4.76 b,c F (3,42) = 25.9 P < 0.005 AMY (μkat.L −1 ) 11.7 ± 3.04 b 17.5 ± 3.60 a 10.1 ± 1.22 b 7.00 ± 2.74 c F (3,42) = 21.1 P < 0.005 LIPA (μkat.L −1 ) 0.45 ± 0.06 a 0.48 ± 0.05 a 0.44 ± 0.06 a 0.56 ± 0.08 b F (3,42) = 6.68 P < 0.005 TCHO (mmol.L −1 ) 4.46 ± 3.87 2.87 ± 1.17 2.29 ± 0.58 3.73 ± 1.96 F (3,42) = 19.6 P = 0.049 ALP 1.51 ± 0.89 b 1.17 ± 0.52 b 0.72 ± 0.42 b 2.77 ± 1.25 a F (3,42) = 10.5 P < 0.005 AST 3.05 ± 2.04 a 1.29 ± 0.61 b 2.68 ± 1.06 a 2.12 ± 0.91 a,b F (3,42) = 6.87 P < 0.005 GLOB (g.L −1 ) 30.8 ± 1.87 a 28.9 ± 3.80 a 26.5 ± 2.0 a,b 21.9 ± 7.40 b F (3,42) = 11.3 P < 0.005 TG (mmol.L −1 ) 7.61 ± 3.02 a,b 9.08 ± 4.89 a 5.71 ± 2.4 a,b 4.41 ± 5.65 b F (3,42) = 2.43 P = 0.092 NH 3 (μmol.L −1 ) 496.3 ± 95 b 871.0 ± 263 a 526.8 ± 65 b 602.6 ± 172 b F (3,42) = 7.23 P < 0.005 TP, Total protein; ALB, Albumin; GLU, Glucose; AMYL, Amylase; LIPA, Lipase; TCHOL, Total cholesterol; ALP, Alanine aminotransferase; AST, Aspartate aminotransferase; GLOB, Globulin; TG, Triglycerids; NH 3 , Ammonia. Values with different superscripts (a, b, c) differ significantly (p< 0.05). Kuc ˇera et al. 10.3389/fmars.2025.1578274 Frontiers in Marine Science frontiersin.org08 and electricity costs (except for the POND group). In the RAS, one of the most important production costs is related to oxygen consumption. Conversely, no oxygen was administered during the trial period in the IPRS and POND groups. Finally, the less significant categories of production costs included consumed tap water and chemicals. Production costs were then corelated with the number of produced fish. This calculation resulted in the following production costs per juvenile: RAS = 4.24 EUR per fish (FBW 190 g), IPRS = 3.05 EUR per fish (FBW 120g) and POND = 21.98 EUR per fish (FBW 62.5g). The production cost of pikeperch juveniles in RAS 22.3 EUR.kg −1 . While in IPRS it was 25.4 EUR.kg −1 and in POND351.9 EUR.kg −1 . The production costs of POND-raised juveniles are presented as an illustration of the economic losses induced by the low SRs. All categories contributing to the final production cost are presented in absolute numbers (EUR) and as percentages (%) in Table 6. 4 Discussion In recent years, an unprecedented increase in energy costs has been observed across Europe. New and less energy-demanding approaches to fish culture should be tested and implemented alongside current aquaculture technologies. Although energyintensive, RASs still offer feasible solutions. Nevertheless the search for new production methods must be encouraged. The presence of vast pond infrastructure in Central and Eastern Europe opens the possibility for diversification through pond aquaculture along with new technological equipment such as the IPRS. To provide comprehensive information on the pros and cons of fish keeping in the RAS, POND and the hybrid IPRS, this study was conducted. Herein, juveniles of pikeperch originating from POND–RAS combined production (Policar et al., 2013)were cultured in the RAS, IPRS and POND to determine growth, feed utilisation, survival and welfare of cultured fish. The SGR of the experimental fish in this study reached 0.7%.d −1 (RAS) and 0.4%.d −1 (IPRS) compared with 0.6%.d −1 (RAS) and 0.6%.d -1 (IPRS) reported by Nagy et al. (2022). The lower SGR may reflect differences in the climate of Southeast Hungary (study published by Nagy et al., 2022) and South Bohemia (present study),particularly in the temperature during the growing season. Moreover, the experiment conducted in Hungary began in June and ended in September, whereas the experimental period in this study began in April and ended in September. At the beginning of the trial, a lower DFR was applied because of the physiological activity of the pikeperch, and their appetite was reduced owing to the lower water temperature in the pond where the IPRS was situated. The SGR of RAS-raised fish was slightly lower in this study (0.7%.d -1 ) than in the other studies focusing on intensive RAS-based pikeperch rearing (Penka et al., 2023,2021,Ronyai and Csengeri, 2008). Pikeperch juveniles in the POND group achieved only 28.3% ± 18.56% WG and an 0.1 ± 0.08%.day −1 SGR. This was likely due to unsuccessful adaptation and an inability to hunt prey fish. Feed utilisation in this study resulted in FCR = 1 g.g −1 (RAS) and 1.6 g.g −1 (IPRS), which is consistent with the findings of other studies on RAS-cultured juvenile pikeperch (Penka et al., 2023,2021; Zimmerman et al., 2019). Nagy et al. (2022) reported an FCR of 2.1 g.g −1 for IPRS-raised fish. A possible explanation for the high FCR in the IPRS, observed in both this study and the one conducted by Nagy et al. (2022), is that fish reared in outdoor conditions were fed to satiation but were unable to fully digest dry pelleted feed because lower oxygen saturation during the second part of the experiment (mornings before sunrise inlate July and August) resulting in slower growth. Additionally, the large tanks in the IPRS combined with the water flow may have discarded some uneaten feed, artificially increasing the observed FCR. Over the last 20 years, extensive research on feed management in RAS-raised pikeperch production has been conducted (Schulz et al., 2007; Ronyai and Csengeri, 2008;Wang et al., 2009;Kowalska et al., 2015;Penka et al., 2023). However, no studies on feed management in IPRS-based pikeperch production have yet been published. Owing to differences in lighting regimes, light intensity, water temperature and quality, turbidity and stocking density, different feeding management practices should be developed and applied to improve feed utilisation in the IPRS. In the RAS, the uneaten feed was properly recorded and subtracted to calculate the exact feed intake. In the ponds, natural predation of prey fish led to an unknown feed intake, which excluded this experimental group from the determination of FCR. The SR is one of the most important production parameters influencing the feasibility of pikeperch culture. The SRs of fish in the IPRS and RAS were statistically similar (88.9% and 83.9% respectively). However, the mortality of fish in the IPRS differed by the size of the deceased fish and the dynamics of mortality, which mostly occurred in two periods. The first period occurred 2 weeks TABLE 6 Production costs of pikeperch juveniles raised in three different production systems. RAS IPRS POND EUR % EUR % EUR % Feed 629 12 491 12 0 0 Tap water 69 1 0 0 0 0 Electricity 380 7 320 8 12.5 0.6 Oxygen 642 12 0 0 0 0 Stocking fish 1786 33 1786 44 1786 92 Chemicals 135 3 77 2 0 0 Personal cost + insurance and tax 1375 26 1069 26 102 5.3 Depreciation 317 6 317 8 34 1.8 FBW (g) 190.0 121.0 62.5 Survival (pcs) 1258 1333 88 Euros per juveniles 4.24 3.05 21.98 Euros per 1kg of juveniles 22.3 25.4 351.9 FBW, final body weight of the raised fish All categories are displayed as absolute numbers (in Euros) and as a percentual share (%). Kuc ˇera et al. 10.3389/fmars.2025.1578274 Frontiers in Marine Science frontiersin.org09