This paper explores the potential of side streams from aquaculture processing and the processing of landed discards from capture fisheries as valuable resources for various applications, including human consumption, animal feed and the production of high-value bioactive compounds. Effective utilisation of these side streams can improve sustainability by reducing waste and increasing resource efficiency in the fisheries and aquaculture sector. Marine aquaculture and capture fisheries are important components of Croatia's maritime economy and play a crucial role in seafood production and the country's economic development. The challenges associated with the processing and utilisation of these resources in Croatia have increased in complexity due to biological, technical and operational factors. The study provides an overview of the opportunities and obstacles in the global utilisation of marine side streams and uses findings from Croatia.

Seaweed is increasingly recognised as a highly nutritious and sustainable food source. While it has a long tradition in many Asian countries, it still only plays a minor role in the Western diet. The aim of this study was to identify and describe consumer segments that are more likely to intend to consume seaweed. An online survey was conducted with 1,621 participants from three Western countries (Australia, the United Kingdom and Croatia) with different cultures, culinary traditions and levels of development in the seaweed industry.Two consumer segments were identified: Food Enthusiasts and Food Conservatives. The profiling of these segments is based on factors oriented to consumers’ food innovativeness, food neophobia, food involvement, food responsibility, health consciousness, and symbolic value. The segments differ significantly in terms of food innovativeness, food neophobia, food involvement, eating and dietary style, past behaviour around seaweed consumption, future intention to eat seaweed and socio-demographic characteristics. These results provide valuable insights for the seaweed industry to develop effective marketing strategies that will meet the demands of different Western consumers.

This study found exceptionally high haplotype diversity within the sampled European sardine populations in the Croatian Adriatic Sea using mtDNA analysis with each individual possessing a unique haplotype. This suggests a high degree of genetic variation within the Croatian sardine populations. Despite high haplotype diversity, the analysis of molecular variance (AMOVA) revealed low genetic differentiation between the two sampled locations (Li & zcaron;njan and Dugi Otok). The majority of genetic variation (92.82%) was found within populations, rather than between them (Fst = 0.072). The median-joining network also did not show a clear separation between the two locations' haplotypes. The low genetic differentiation and lack of clear separation in the haplotype network suggest high gene flow between the Li & zcaron;njan and Dugi Otok populations. This might be attributed to the proximity of the two sampling sites and the high dispersal potential of sardine larvae. While overall genetic differentiation was low, the presence of unique haplotypes in each individual and slight variations in haplotype frequency between locations hints at the possibility of local adaptation or micro-evolutionary processes influencing the sardine populations. Further investigation with larger sample sizes across a wider geographic area is needed to explore this possibility.

Sardines and anchovies are the most important small pelagic species throughout the Mediterranean, caught mainly by purse-seiners. Their rapid bacterial degradation after capture and storage limits their commercial use and shelf life. Gills are the most vulnerable tissue in fish, harboring bacterial communities which have not been previously investigated in these species. This study examined cultivable bacteria from gills of harvested sardines and anchovies, tanks in which they are stored aboard, and fishing nets on four occasions (twice for both warm and cold seasons). A total of 471 bacteria were isolated, belonging to 74 genera and 163 species by MALDI-TOF MS identification. A number of genera and species identified from fish and surfaces occurred only in the warm or cold season, but a fraction occurred in both seasons. Sardine gills harbored most of the isolated bacteria (254), belonging to 53 genera and 111 species, as opposed to anchovy with 120 strains, belonging to 30 genera and 64 species. A diverse cultivable bacterial community consisting of 17 species was isolated exclusively from the polyethylene surfaces of nets and tanks. This finding is significant regarding their potential migrations between planktonic and sessile lifestyles. Possible contamination and cross-contamination are likely to increase with the rise in ambient and seawater temperature during the hauling and sorting of fish in the tanks. The food safety risks stem from pathogens and fish spoilage bacteria on both the fish and the surfaces of fishing nets and storage tanks.

Environmental DNA (eDNA) is defined as genetic material taken from an environmental sample that contains distinguishing characteristics of the original organisms that are or were present in the environmental sample and includes extracellular and intracellular DNA. Its presence and degradation depend on various abiotic conditions, and possible sources of eDNA include all biological materials of organisms. The analysis of eDNA is simple and cheap. It is of great importance for the study of environmental biodiversity because it provides quantitative estimates of the abundance and biomass of individuals and species. Changes in environmental conditions affect eDNA, which is why eDNA analysis is often used in ecology. In addition to climatic changes, there are also seasonal changes in abiotic factors that significantly affect eDNA abundance. In this study, the research methods and application of this genetic material in different research areas are presented.

The aim of the study was to evaluate the growth, fatty acid profile and concentration of malondialdehyde of muscle tissue of meagre Argyrosomus regius fed diets with different lipid content. The long-term experiment was conducted in three feeding groups: A (CP = 52.0; CL = 21.0), B (CP = 56.0; CL = 18.0), C (CP = 48.0; CL = 16.0) with two replicates in marine net cages on Bisage Island, Adriatic Sea over 20 months. At the beginning of the experiment, fish were of equal weight (6.83 ± 1.03 g) and length (8.57 ± 0.49 cm) and were fed to satiation during the experiment. At the end of the experiment, the fish from each feeding group (n = 110) were measured and muscle tissue was collected (n = 60) and stored at −80 °C until analysis. The final weight and condition factor were significantly different (p < 0.05) between the groups. The highest ratio of crude fats and n-3/n-6-fatty acids was found in the muscle tissue of group A. Fish fed diet A also exhibited higher MDA levels compared to fish in the other feeding groups, indicating elevated levels of lipid peroxidation in muscle tissues. Experimental feeding group A showed better growth performance, a higher content of the beneficial fatty acids EPA and DHA and a more favorable n-3/n-6 ratio than feeding groups B and C. Continuously monitoring and adjusting feeding protocols in accordance with lipid content and fatty acid composition could maximize growth and health outcomes in meagre farming.

Agrivoltaics and aquavoltaics combine renewable energy production with agriculture and aquaculture. Agrivoltaics involves placing solar panels on farmland, while aquavoltaics integrates photovoltaic systems with water bodies and aquaculture. This paper examines the benefits and challenges of agrivoltaics and aquavoltaics, focusing on their potential for Croatian agriculture and freshwater aquaculture. Benefits include dual land use, which allows farmers to produce clean energy while maintaining agricultural practices. They diversify renewable energy sources and reduce dependence on fossil fuels and greenhouse gas emissions. Solar panels in agrivoltaics provide shade, protect crops, reduce water needs, and increase yields. Challenges include high initial costs and limited accessibility, especially for small farmers. Integration with existing systems requires careful planning, considering irrigation, soil moisture, and crop or fish production. Maintenance and cleaning present additional challenges due to dust, debris, and algae. Policy and regulatory frameworks must support implementation, including incentives, grid integration, land use regulations, and conservation. The location, resources, and crops grown in Croatia present an opportunity for agrivoltaics and aquavoltaics, considering cultivation methods, species, and regulatory requirements.

Green ormer or European abalone is an ecologically and economically important mollusk that finds food in the marine ecosystem and is also a delicacy for humans. Therefore, numerous studies have been conducted on this species in order to cultivate it as successfully as possible in new habitats. Mollusks are affected by bottom trawling and seafood disturbance while seasonal variations in oceanographic factors also affect their physiology, stress responses, and survival. In this review, an overview of numerous studies on the distribution and influence of various ecological factors on this species is presented, along with a morphological description of green ormer. In addition, the factors that influence maturation, reproduction and growth, as an important part of the breeding process, are presented. Emphasis is also placed on the natural diet as well as the diet in breeding farms. The physiology of this species lists numerous factors that affect its growth, especially antioxidant stress. There are a considerable number of knowledge gaps in the history of ormer aquaculture, which are pointed out together with their solutions, providing the opportunity to expand the cultivation of this species.

Along with growing consumer awareness about the impact of food on health, there is a trend towards increasing fresh fish consumption. At the same time, the demand for organic food is increasing in the modern market. Although fruits, vegetables and nuts have the biggest share in the organic food market in Europe, the aquaculture production of organic fish is also growing. Therefore, the main aim of this study is to explore the knowledge and perception of Croatian consumers about fresh fish from organic farming. An online and face-to-face survey was conducted on a sample of 303 respondents. Data analysis (univariate and bivariate) was performed using SPSS Statistics for Windows. Most consumers have medium and low subjective knowledge about fresh fish from organic farming, and objective knowledge about fresh fish from organic farming is low. Only half of the consumers are aware that they can buy fresh fish from organic farming in the domestic market. Half of the consumers have already consumed fresh organic fish, and half are willing to pay a higher price for fresh fish from organic farming. Compared to fresh fish from conventional farming, respondents consider fresh organic fish to be healthier, tastier and to have less fat, but also more expensive and less available.

The aim of this study was to compare the organismal responses of farmed and wild-caught turbot, Scophthalmus maximus, based on analyses of biochemical plasma parameters, leukocyte profile, and histological tissue profile of gills, kidney, liver, intestine, and spleen, as well as gene expression of stress proteins in kidney and liver tissue. The results revealed significant differences in plasma triglycerides (TRIG), total protein (TP), albumin (ALB), globulin (GLOB), bilirubin (TBIL), creatinine (CRE) levels, creatine kinase (CK), and superoxide dismutase (SOD) activities that were higher, and A/G ratio, calcium (Ca) and phosphorus (P) concentrations, alkaline phosphatase (ALP), and glutathione peroxidase (GPx) activity, which were lower in farmed population. The neutrophil-leukocyte (N:L) ratio and gene expression of HSP70, HSP90, and WAP65-2 were increased in the wild-caught turbot. The wild-caught turbot were infested with the gill digenean parasite Dactylogyrus sp. and tapeworm Bothriocephalus scorpii. The obtained results provide valuable data for the assessment of the physiological responses of turbot for future comparative studies of the effects of various endogenous and exogenous factors on homeostasis of this species.

The littoral zones of freshwaters are highly susceptible to extreme hydrological fluctuations caused by climate-induced changes in the water cycle. Disturbances in the hydrology could affect fish assemblages and their trophic interactions with invertebrates, which constitute a large part of fish diets. In 2014 and 2015, the littoral zone of the Sava River (Croatia) was studied to determine the influence of hydrological extremes on (1) fluctuations in environmental drivers and biocoenoses, and (2) the trophic relationships between fish, macroinvertebrates and zooseston, in an attempt to reveal their trophic interactions. Biocoenotic components showed different tolerance to extreme discharge, resulting in remarkable reductions in fish abundance, diversity, biomass, size and, presumably due to dilution, the abundance of zooseston, which is an important food for fish larvae. By contrast, benthic macroinvertebrates did not show significant fluctuations in abundance, but the share of benthic groups of organisms was shifted during high discharge. Gastropods and amphipods were found to be important food sources for fish. The present study helps to highlight the consequences of hydrological disturbances caused by climate change: the enhancement of stressors in riverine littoral habitats and inhabited communities.

In the shallow Northern Adriatic, marine mollusks are affected by bottom trawling and seafood disturbance. Seasonal oscillations of oceanographic factors additionally influence their physiology, stress responses and survival. Tissue responses to seasonal variations in green ormer (Haliotis tuberculata L.) and Mediterranean scallop (Pecten jacobaeus L.) in the Northern Adriatic have not been reported. Hence, their biochemical and antioxidant defense properties over seasons were studied and the microanatomical structure of their tissue was correlated with function. Histological analysis of gonads revealed two peaks of gonadal maturation and spawning during the spring/summer period and winter season for scallops, and one peak during the fall for ormers. The gonadal maturation of both species was correlated with their seasonal variations of metabolic demands and antioxidant capacity. The lipid vacuoles of tubuloacinar terminations in the digestive gland differed between the two species; in scallop they are several-fold larger in size and number. Low temperatures in winter contributed to a decline in enzymatic antioxidant defense in scallop tissues, having lower superoxide dismutase (SOD) and glutathione peroxidase (GPx) activity, and higher concentrations of thiobarbituric acid reactive substances (TBARS) and total antioxidant status (TAS). In ormers, winter induced lower TAS, TBARS, SOD and GPx concentrations. The significant difference of winter TAS and TBARS levels between ormers and scallops was correlated with variations in their reproductive cycles, as well as in antioxidant defense systems. The most important factor for stress-related parameters for both species in this work was found to be the season-induced temperature change.

A ten-week feeding trial was carried out to investigate the effects of replacing fishmeal (FM) with soybean meal (SBM) and brewer’s yeast (BY) on growth performance, blood parameters, oxidative stress and micromorphology of liver and intestines in brown bullhead ( Ameiurus nebulosus L.). Fish were fed nine feeds in which FM was replaced with 25%, 50%, 75% and 100% SBM (K1, K2, K3 and K4) and 17% + 8%, 42% + 8%, 67% + 8% and 92% + 8% of SBM/BY combination (K5, K6, K7, K8). Growth indices showed greater outcomes for the K2 group in comparison to all other groups. A decrease in plasma cholesterol and triglycerides concentrations was found after FM replacement. Activity of SOD was higher in groups K4, K7 and K8. The early inflammatory indications with abnormal vacuolization of lamina propria and basal epithelium were present in diets K4 and K8. Hepatocytes were irregular in shape with signs of inflammatory reaction in diet K8. A decreased perimeter of hepatocyte nuclei was detected in all experimental diets when compared with the control. This study demonstrates that the optimal replacement of FM with SBM/BY in brown bullhead diets contains up to 50% of FM replaced with SBM in order to obtain advantageous growth performance and adequate health condition.

The present work is the first study of Mediterranean scallop (Pecten jacobaeus) biochemical properties, antioxidant defenses, and free radical scavengers during the yearly seasons in the Northern Adriatic, off Istria. Scallop nutrient reserves (glucose, triglyceride, and cholesterol) in four tissues under examination were positively correlated and were predominant in digestive gland and gonad. The muscle energy maxima were in correlation with the maximum fall gonosomatic index (GSI), when diatoms and coccolithophorids thrive. The decrease of GSI in summer might be related to the spawning or resorption of gametes. Summer also revealed elevated levels of glucose in gonad and digestive gland, while muscle glucose and cholesterol significantly varied in spring vs. winter samples. In relation to the diatom seasonal abundance, carotenoids, namely astaxanthin peaks were found in digestive gland, which, being stimulators of calcium transport over cell membranes, could have contributed to the high digestive gland levels of calcium in winter. In winter, total antioxidative status (TAS) of scallop tissues was 3-fold higher than in other seasons, particularly in digestive gland, having a significant correlation with magnesium, a regulatory tool in oxidative processes. The winter maxima of TAS and thiobarbituric acid reactive substances TBARS in relation to summer maxima of glutathione peroxidase and superoxide dismutase in digestive glands indicate to a decrease in antioxidant defense during cold months, and are related to the accumulation of lipid peroxidation products (such as malondialdehyde) in digestive gland of scallops. Although the increased susceptibility to oxidative stress could be attributed to winter temperature, other factors such as the gonad maturation, availability of food supply, and salinity might counteract that effect. The seawater alterations of salinity, temperature and water quality are in relation to the river Po influx, which is very likely to influence the physiological and biochemical responses of scallops in the Northern Adriatic.

Croat J Fish continues in its effort to stay an important scientific and professional journal in the region. In this year, the Journal was advanced by new Editorial Board members while cooperation with SCIENDO publishers has been extended until the end of 2020. We hope and expect 2019 to be yet another significant year in fisheries science and we look forward to sharing it with you. The Editorial also provides information on the latest news on Open Access Journals Initiative, the Journal Scopus CiteScore metrics, as well as the articles published in Croat J Fish in 2018, with a list of reviewers who participated in the review process.

AbstractDue to the cyclic or systemic nature of both aquaponics and organic production, organic certification appears to be a natural step for a researcher, system designer or commercial-oriented aquaponics producer to engage in. However, the underlying principles and justifications of aquaponics and organic production differ considerably between respectively a technological- and a soil-based understanding of nutrient cycles and long-term sustainability in food production. These principles are confirmed in both the organic regulation regime of the EU and USA, and presently leave the question ambiguously open as to whether aquaponics as a food production system can be recognized and certified as organic. Despite an openness in the organic regulation for new knowledge, adaptations and innovations, the organic sector itself has shown a reluctance to recognize more knowledge-based intensive speciality crops and technologies. This is particularly difficult with respect to small organic sub-sectors such as horticulture and aquaculture production. Both are very specific subsystems of the agricultural sector, where aquaponics potentially would belong at the intersection between organic greenhouse horticulture and organic aquaculture. Organically certified aquaponics would therefore need to establish a niche within the organic sector. So in order to move forward, there is a great need for a more serious but open-minded exchange and discussion among the aquaponics and organic sub-sectors themselves to explore the potential but also limitations of their respective production models. However, between the two food production systems, there should be room for debate with a view to finding new and feasible roles for aquaponics in the organic community.