Daniel Matulić

ZOOPLANKTON STRUCTURE IN TWO INTERCONNECTED PONDS: SIMILARITIES AND DIFFERENCES

Abstract The research of zooplankton diversity, abundance and trophic structure was conducted during the summer period in pelagial zone on the longitudinal profile of the Sutla River Backwater. Investigated site consists of two interconnected basins: transparent Upper Basin with submerged macrophytes and turbid Lower Basin without macrophytes in the littoral zone. In the Upper Basin, abundance and diversity of zooplankton in the pelagial was higher in comparison to the Lower Basin, with prevailing species of genus Keratella as microfilter-feeder, and genera of Polyartha and Trihocerca as macrofilter-feeder rotifers. On the contrary, in the Lower Basin, crustaceans dominated in abundance. Microfilter-feeder cladoceran (Bosmina longirostris) and larval and adult stages of macrofilter-feeder copepod (Macrocyclops albidus) prevailed in the Lower Basin. Fish predation pressure was more pronounced in the pelagial of the Upper Basin, indicated by low cladoceran abundance in the surface layer. Although the studied basins were interconnected, results indicate significant (Mann-Whitney U test, p < 0.05) differences in the zooplankton structure as a potential result of the macrophyte impact on environmental conditions and fish predation pressure.

Growth performance, fatty‐acid composition, lipid deposition and hepatic‐lipid metabolism‐related gene expression in juvenile pond loach Misgurnus anguillicaudatus fed diets with different dietary soybean oil levels

A 10 week feeding trial was conducted to evaluate the effects of different dietary soybean oil (SO) levels on growth performance, fatty-acid composition and lipid deposition in viscera, histology and histochemistry of liver, intestine and hepatic-lipid metabolism-related gene expressions in pond loach Misgurnus anguillicaudatus juveniles. Misgurnus anguillicaudatus (mean ± s.d. mass 0·40 ± 0·01 g) were fed five experimental diets containing SO at different concentrations: 0, 20, 32, 56 and 100% SO and a diet containing 100% fish oil (100% FO). The mass gains and specific growth rates of M. anguillicaudatus fed 20% SO and 100% FO diets were significantly higher than those of the other groups (P < 0·05). The lipid content of viscera and the amount of cytoplasmic vacuolation in the liver increased with incremental dietary SO level. Meanwhile, increasing dietary SO levels up-regulated the messenger (m)RNA levels of lipogenic genes (such as Δ6fad, scd, pparγ, fas and srebp-1) and down-regulated the mRNA levels of the lipolytic genes (such as pparα, cpt1, atgl and hsl) in the liver. The percentage of 20:4n-6 significantly (P < 0·05) increased with increasing dietary SO level, which might be correlated with the up-regulation of the mRNA level of Δ6fad. The highest levels of dietary SO, however, had a negative effect on growth performance, lipid deposition of viscera and histology and histochemstry of liver and intestine. The increased lipid accumulation induced by incremental dietary SO level probably occurred through different strategies for lipid metabolism as a result of competition between lipolysis and lipogenesis and between export and import of lipids in this species.

What determines fresh fish consumption in Croatia

Although fresh fish is widely available, consumption still remains below the recommended intake levels among the majority of European consumers. The economic crisis affects consumer food behaviour, therefore fresh fish is perceived as healthy but expensive food product. The aim of this study was to determine the factors influencing fresh fish consumption using an expanded Theory of Planned Behaviour (Ajzen, 1991) as a theoretical framework. The survey was conducted on a heterogeneous sample of 1151 Croatian fresh fish consumers. The study investigated the relationship between attitudes, perceived behavioural control, subjective norm, moral obligation, involvement in health, availability, intention and consumption of fresh fish. Structural Equation Modeling by Partial Least Squares was used to analyse the collected data. The results indicated that attitudes are the strongest positive predictor of the intention to consume fresh fish. Other significant predictors of the intention to consume fresh fish were perceived behavioural control, subjective norm, health involvement and moral obligation. The intention to consume fresh fish showed a strong positive correlation with behaviour. This survey provides valuable information for food marketing professionals and for the food industry in general.

First record of palmetto bass (Morone saxatilis x M. chrysops) in the Croatian part of the river Danube

On October 19, 2010, a male specimen of palmetto bass (Morone saxatilis x M. chrysops) was caught by commer- cial fishing net in the Croatian section of the river Danube (302 mm TL and 331 g). It was in its third year of age (2+). A condition factor of 1.20 was based on the total length. Six specimens of prey fish were found in its gut (22.97 g altogether). Morphometric and meristic traits of this palmetto bass are presented and its possible threat to the fish community is dis- cussed.

Microsatellite-based genetic variability and differentiation of hatchery and feral common carp Cyprinus carpio L. (Cyprinidae, Cypriniformes) populations in Croatia.

Common carp production has an important status in Croatian aquaculture. In addition, the sport fishing of common carp in open waters is very popular, but it is often based on stocking from fish farms. Using fifteen microsatellites, 243 individuals from 5 hatchery and 5 feral populations have been analyzed. A total number of 148 alleles were recorded. However, the mean number of alleles per locus was remarkably low. Pairwise FST values (0.026-0.130) were significant (P<0.01), demonstrating differentiation among populations. The Markov chain method test showed that all the popula- tions deviated from HWE (P <0.05). After sequential Bonferroni correction only the Vrana lake was in HWE in all the loci but MFW20. The factors that may result in genetic divergence and significant reduction of the observed heterozygosity are discussed. AMOVA results for 10 populations indicate that the percentage of the variation among populations was 6.26%, which is lower than the variation within populations (91.04%).

The common carp Cyprinus carpio in Croatia (Danube and Adriatic basins): a historical review

This review provides the first historical account of the ecology and biology of common carp Cyprinus carpio in the Danube and Adriatic basins of Croatia, and emphasises the species’ economic relevance and management implications. As a semi-native species that is native to the Danube but translocated across the Adriatic Basin, carp plays an important role for aquaculture, recreational and artisanal fisheries. However, original strains have now disappeared, and because of genetic pollution in inland waters there is an increasing demand for restoring populations of the now rare and threatened wild carp, making conservation measures a priority. Translocations of carp across water bodies of the Adriatic Basin mostly for food supply did not prove successful in the long term, as the resulting ecological impacts may have been higher than the expected economic advantages. Measures for the prevention of further (uncontrolled) carp re-stocking are therefore necessary and this will require closer collaboration between scientists and environmental managers.

Effects of dietary vitamin C and soybean lecithin in the nutrition of brown bullhead ( Ameiurus nebulosus L.) fingerlings

The effects of different forms of vitamin C and soybean lecithin on growth performance, feed utilization and body composition of brown bullhead (Ameiurus nebulosus, Lesuer 1819) were evaluated during a 9-week growth trial. A special interest was to investigate a possible combine effect of these nutritional components. The diets used contained three forms of vitamin C (crystallized ascorbic acid, encapsulated L-ascorbic acid and Ca-L-threonate) (100 mg/kg) with and without the combination of soybean lecithin. Besides control diet (K), one more diet was supplemented with soybean lecithin (L) only. One-hundred-ninety-two brown bullhead of about 45 g initial body weight was randomly divided in 24 tanks (115 L each). Testing conditions included 8 fish per tank, with triplicate tanks for treatment. All diets with supplemented components had higher final weight. Specific growth rate, feed conversion rate and condition factor were significantly higher with encapsulated vitamin C diets (CC, CCL), followed by the results of enriched ascorbic acid diets. Vitamin C and lecithin supplementation showed positive influence on significantly higher number of erythrocytes, haematocrit, triglycerides and total protein. Vitamin C content of muscle and liver tissue was not uniform and was significantly higher in AAL, CCL, CC and AA feeding groups. The fatty acids profile of muscle and liver tissue showed that phospholipids from soybean lecithin and vitamin C diets enhanced the quality of usable part of the fish body. Combine supplementation of vitamin C and soy lecithin indicated positive production effects, but did not cause a statistically significant difference.

Long-term analysis of fish assemblage structure in the middle section of the Sava River – The impact of pollution, flood protection and dam construction

At the beginning of the 20th century, the middle section of the Sava River in Croatia was unaffected by major human activities and rich in ichthyofauna. The Sava River was important for commercial and recreational fishing for the local population, which still remains today. However, the 1920s mining industry was established in Slovenia, which emitted carbon dust into the Sava River. At the same time, the construction of embankments to mitigate flooding started in the middle section. Furthermore, in the 1980s, the Krško nuclear power plant (NPP), and in the 2010s, the Krško hydropower plant (HPP) were built in Slovenia. These activities could have an impact on the composition of fish communities downstream from the major sources of disturbances. Therefore, the main aim of this paper were to analyze the changes in fish assemblages of the Sava River from 1978 to 2017, prior to and after the construction of Krško NPP and HPP at the Medsave site on the Sava River, 20 km downstream from the major construction operations. Collected data were divided into four sampling periods (SP): SP1, from 1978 to 1980; SP2, from 1991 to 1994; SP3, from 2001 to 2006, and SP4 from 2011 to 2017. Besides alien fish species, water quality and hydromorphological modifications were identified as significant stressors. In SP1 and SP2 limnophilic and eurytopic fish groups were predominant, and 26 different fish species were identified, but in SP3 and SP4 rheophilic fish groups become dominant, and the diversity has declined to 21 species. Threatened species blageon, Telestes souffia seems to be missing from the main course of the Sava River in last 20 years. It can be concluded that disturbances in the fish assemblage pattern have coincided with the presence of multiple stressors of human origin.

EDITORIAL 2018: The Croatian Journal of Fisheries: Ribarstvo 80th Anniversary

Abstract The Croatian Journal of Fisheries (Croat J Fish) was launched 80 years ago, in 1938, as Ribarstvo, so the current issue of Croat J Fish celebrates this significant event. Since 1992, the Journal was issued quarterly on a regular basis under the name Ribarstvo. However, in 2012 the Journal changed its name to Croatian Journal of Fisheries: Ribarstvo to attract more international audiences. The scope of the Journal has not changed much during its development and has mainly focused on ichthyology, aquaculture, ecology, fish pathology, marine and inland waters and other issues related to fisheries. Nowadays, the Journal tends to be a highquality open-access scientific journal, visible online, of interest to a wide scientific community. Expanding the number of international associate editors also indicates this process. In the segment of publishing strategies, more effort is needed to increase citation activity of the Journal. The Editorial 2018 also provides information on the articles published and the list of reviewers who participated in the review process in 2017.

WILD-CAUGHT VERSUS FARMED FISH – CONSUMER PERCEPTION

Abstract We have limited knowledge of determinants of consumer preferences for wild-caught versus farmed-raised fish, so this work aims to investigate the impact of sociodemographics, habits and frequency of fresh fish consumption, such as involvement in cooking, on the preferences for wild versus farmed fish. A survey was done on a sample of 1151 fish consumers in Croatia. Results showed that female, older consumers, consumers with higher income and those living in coastal parts of Croatia give higher preferences for wild fish and they detect differences between the taste of wild and farmed fish. Consumers with higher levels of habits of fresh fish consumption, who eat fresh fish often and are more involved in cooking, prefer wild-caught fish. These findings provide valuable information for the aquaculture sector, especially for planning marketing strategies for the promotion of farmed fish.