Sprattus Sprattus Research Articles

Limited Parallelism in Genetic Adaptation to Brackish Water Bodies in European Sprat and Atlantic Herring.

The European sprat is a small plankton-feeding clupeid present in the northeastern Atlantic Ocean, in the Mediterranean Sea, and in the brackish Baltic Sea and Black Sea. This species is the target of a major fishery and, therefore, an accurate characterization of its genetic population structure is crucial to delineate proper stock assessments that aid ensuring the fishery's sustainability. Here, we present (i) a draft genome assembly, (ii) pooled whole genome sequencing of 19 population samples covering most of the species' distribution range, and (iii) the design and test of a single nucleotide polymorphism (SNP)-chip resource and use this to validate the population structure inferred from pooled sequencing. These approaches revealed, using the populations sampled here, three major groups of European sprat: Oceanic, Coastal, and Brackish with limited differentiation within groups even over wide geographical stretches. Genetic structure is largely driven by six large putative inversions that differentiate Oceanic and Brackish sprats, while Coastal populations display intermediate frequencies of haplotypes at each locus. Interestingly, populations from the Baltic and the Black Seas share similar frequencies of haplotypes at these putative inversions despite their distant geographic location. The closely related clupeids European sprat and Atlantic herring both show genetic adaptation to the brackish Baltic Sea, providing an opportunity to explore the extent of genetic parallelism. This analysis revealed limited parallelism because out of 125 independent loci detected in the Atlantic herring, three showed sharp signals of selection that overlapped between the two species and contained single genes such as PRLRA, which encodes the receptor for prolactin, a freshwater-adapting hormone in euryhaline species, and THRB, a receptor for thyroid hormones, important both for metabolic regulation and the development of red cone photoreceptors.

Modeling of the habitat suitability of European sprat (Sprattus sprattus, L.) in the Adriatic Sea under several climate change scenarios

The Mediterranean Sea represents the lower latitudinal limit of the European sprat range, where it is considered a sentinel species favoring temperate–cold temperatures. Sprattus sprattus is a plankton feeder that plays an important ecological role in contributing to the transfer of energy from lower to higher trophic levels, but climate-driven increases in sea temperatures may reduce the suitability of the pelagic habitat and threaten the tropho-dynamic role of sprat in areas such as the Adriatic Sea. The latter is an enclosed basin characterized by shallow waters and high annual temperature variations. Here, to investigate present and future habitat suitability areas for sprat, we applied four species distribution models (SDMs) using fishery-independent data collected from 2004 to 2021, along with remotely sensed and modeled environmental variables. A set of nine environmental predictors was tested, and the resulting best model was averaged in an ensemble model approach. The best ensemble models revealed good to high accuracy (sensitivity and specificity ≥ 0.8). The sea surface temperature and chlorophyll concentration emerged as the main explanatory variables in predicting the potential habitat of sprats, followed by bathymetry. The resulting probability of occurrence maps revealed that the species is bounded in the northern Adriatic Sea, where a longitudinal shift of high-suitability habitats from inshore to deeper and colder waters was detected between early and late summer. Future projections under IPCC representative concentration pathway (RCP) scenarios 4.5 (intermediate emission) and 8.5 (high emission-warm) underline small changes along with a gain of new areas in late summer in the short-term period up to 2050. Conversely, the temperature increase projected for the end of the century is predicted to cause a loss of suitable habitat area for sprats of up to 88% under a high emission-warm scenario relative to current habitat occupancy throughout the basin.

Winter Time Ichthyoplankton Assemblages Following Dense Mucilage Event in the Sea Of Marmara, Türkiye

The community structure of ichthyoplankton after mucilage was investigated. For this purpose, three ichthyoplankton survey were conducted from 34 stations between December 2021 and March 2022. A total of 19 fish egg and 16 fish larvae species were identified. It was detected that the biodiversity of winter time ichthyoplankton was higher than previous studies. European Sprat, Sprattus sprattus had the highest mean biomass for both fish eggs and fish larvae, whereas Sardine, Sardina pilchardus had relatively low biomass. Karacabey Floodplain area, Büyükçekmece estuarine area and Erdek Bay were the most important spawning areas for winter spawners. It was found that ecosystem health of the Marmara Sea was suitable for fertilization, hatching and larval growth soon after the mucilage and hydrological regime recover itself immidiatelly.

Chick diet in UK Little Terns Sternula albifrons

ABSTRACT Capsule We studied the diet of Little Tern chicks in the UK using new data collected as part of the EU LIFE-funded Little Tern Recovery Project (2014–2018) (the LIFE Project), which shows that, despite a wide variety of prey items being recorded, diet at UK colonies is dominated by two types of lipid-rich marine fish: sandeel Ammodytes spp. and clupeid species (Atlantic Herring Clupea harengus and European Sprat Sprattus sprattus). Aims To analyse data on the diet of Little Tern chicks from the LIFE Project and assess what additional insight these provide in comparison to the findings in previous literature. Methods Timed chick-feeding observations were made at 12 English and Welsh Little Tern colonies between 2014 and 2018 and compared to descriptions of chick diet from other UK studies (published and unpublished). Results Chick diet data from the LIFE Project were dominated by lipid-rich marine fish, principally sandeels and clupeid species (82% of all recorded prey items). Adult Little Terns feeding chicks with crustaceans or other invertebrates were recorded at 75% of colonies, but there was no evidence that these routinely made up a substantial proportion of chick diet. We found no significant inter-annual differences in diet composition between individual colonies. However, analysis of records of chick diet over a longer time series (Long Nanny colony in Northumberland, with data available for 17 of the years between 1998 and 2018) showed some significant differences in diet composition between years. Conclusion Although Little Terns are generalist feeders, 82% of the prey diet consisted of two prey types: sandeels and clupeids. This may leave existing UK Little Tern colonies vulnerable to any future climate change impacts affecting either the distribution or nutritional quality of their main prey species.

Influence of Pre-Treatment on the Seasonal Variation of Smoked Baltic Sprat Texture and Color

The seasonal variation of Baltic sprat chemical composition leads to a change in smoked fish texture and color, which may pose challenges for industrial processing. This research aimed to evaluate the dependence of smoked sprat texture and color on the catching season and pre-treatment applied before the smoking of fish, following one year of frozen storage. Various proportions of sodium chloride (NaCl), calcium chloride (CaCl2), and acetic acid were used in the solution for fish pre-treatment. The introduction of salts during the pre-treatment process for late-season fish has been found to enhance the texture of the smoked product. The color components of the lightness (L*) and redness (a*) measured on the smoked fish surface remained consistent throughout the catching season, whereas the yellowness (b*) showed a tendency to decrease towards the end of the season. Moreover, when acetic acid was applied to late-season fish, the yellowness of the smoked sprat surface increased compared to that of the sample without this pre-treatment. These findings suggest that the choice of pre-treatment methods can significantly improve the texture and color attributes of the smoked sprat, which is crucial for maintaining quality standards, especially in the context of industrial processing.

Otolith biochronology for the long-term reconstruction of growth and stock dynamics of fish

Long-term biological time series are essential to evaluate previous responses of organisms to alterations in the environment. Biochronological methods based on archival fish otoliths allow setting such time series, but their predictive potential as proxies of past environmental conditions is still underexploited. In this study, we reconstructed growth variation in European sprat (Sprattus sprattus) in the Baltic Sea from 1956 to 2020 based on measurements of the archived otoliths. We used otolith annual increment widths as a proxy of fish somatic growth. We showed significant negative relationships between sprat growth and sprat spawning stock biomass (SSB) associated with strong intraspecific competition for limited food resources. We also identified a link between sprat growth and water salinity—indicator of the ecosystem's hydrological situation. For the first time, we estimated the SSB prior to the period of available historical data based on the otolith-derived information on the past growth variation. This estimation was based on the strong relationships between SSB and fish growth, complemented with temperature and salinity variables as predictors (R2 = 0.62). A model trained on at least 40 years of data from the more recent past allows us to robustly back-estimate SSB. This study provides new multidecadal data, giving insights into environmental factors affecting the growth of Baltic sprat, and demonstrates the potential of otolith-based biochronology for the provisioning of independent indices of the historical fish stock size. The proposed methodological approach broadens the portfolio of possible applications of the biochronology time series to indicate past changes in the aquatic environment.Graphical abstract

Summer Biomass Variability and Spatial Interactions between European Sprat (Sprattus sprattus) and Moon Jellyfish (Aurelia aurita) in the Western Part of the Black Sea

Over the past few decades, various causal connections between commercial small pelagic fish species and gelatinous zooplankton have been reported in the Black Sea, which affect the pelagic ecosystem. Recently, moon jellyfish regained dominance among gelatinous plankton; however, biomass fluctuations and interactions with small pelagic fish remain poorly understood. During the summers of 2019–2022, scientific pelagic trawl surveys in the Western Black Sea enabled simultaneous monitoring of small pelagic fish biomass, with sprat as the key species and moon jellyfish as an incidental catch. In total, 153 trawl hauls were conducted across four depth strata from 15 to 100 m, and a “swept area” method was used for biomass estimation. The sprat stock biomass ranged from 10,698 to 29,177 t, with an average value of 19,432 ± 4834 t. The total biomass of moon jellyfish was 2002 ± 868.73 t, and dense aggregations were observed in the coastal waters during certain years. Two scenarios of spatial interactions between planktivorous species were identified and linked to the formation of A. aurita aggregations. We found that changes in jellyfish density were associated with weak-to-moderate effects on the spatial distribution of sprat assemblages in coastal areas.

Properties of Degradable Polyhydroxyalkanoates Synthesized from New Waste Fish Oils (WFOs).

The synthesis of PHA was first investigated using WFOs obtained from smoked-sprat heads, substandard fresh sprats, and fresh mackerel heads and backbones. All the WFOs ensured the growth of the wild-type strain Cupriavidus necator B-10646 and the synthesis of PHA, regardless of the degree of lipid saturation (from 0.52 to 0.65) and the set and ratio of fatty acids (FA), which was represented by acids with chain lengths from C14 to C24. The bacterial biomass concentration and PHA synthesis were comparable (4.1-4.6 g/L and about 70%) when using WFO obtained from smoked-sprat heads and fresh mackerel, and it was twice as high as the bacterial biomass concentration from the fresh sprat waste. This depended on the type of WFO, the bacteria synthesized P(3HB) homopolymer or P(3HB-co-3HV-co-3HHx) copolymer, which had a lower degree of crystallinity (Cx 71%) and a lower molecular weight (Mn 134 kDa) compared to the P(3HB) (Mn 175-209 kDa and Cx 74-78%) at comparable temperatures (Tmelt and Tdegr of 158-168 °C and 261-284 °C, respectively). The new types of WFO, studied for the first time, are suitable as a carbon substrates for PHA synthesis. The WFOs obtained in the production of canned Baltic sprat and Baltic mackerel can be considered a promising and renewable substrate for PHA biosynthesis.

Synthesis and Properties of Polyhydroxyalkanoates on Waste Fish Oil from the Production of Canned Sprats

The waste fish oil obtained from Baltic sprat waste in the production of canned sprats was studied as a sole carbon substrate for PHA synthesis by the wild-type strain Cupriavidus necator B-10646. Sprat oil contained a set of fatty acids with a chain length from C14 to C24, saturation factor 0.63, and provided bacterial growth and PHA synthesis. Bacteria metabolized fatty acids unevenly utilizing polyenoic acids and not using monoenoic and saturated acids. The bacterial biomass yield and the intracellular polymer concentration were 6.5 ± 0.5 g/L and 65 ± 5% by fed-batch culture in flasks. The synthesized PHAs were three-component copolymers with a predominance (97–98 mol.%) of 3-hydroxybutyrate monomers and small inclusions of 3-hydroxyvalerate and 3-hydroxyhexanoate; the ratio of monomers changed slightly depending on the sprat oil concentration. The series of samples had a temperature (Tmelt) of 158–165 °C, a molecular weight (Mw) of 540–760 kDa, and a degree of crystallinity (Cx) of 66–72%. For the first time, the waste fish oil from the production of sprats studied as a carbon substrate is a promising, affordable, and renewable substrate for PHA biosynthesis.

Уловы и биологические показатели шпрота (Sprattus sprattus balticus, Clupeidae) в российских водах Финского залива на современном этапе

Paper presents the data about the catches of the Baltic sprat in the Eastern part of the Gulf of Finland from 1995 to 2021. The size and age characteristics of the sprat taken during the trawl fishing in autumn 2020-2021 are given. The analysis of nutrition and maturation, feed base and the factors limiting the fish growth is carried out.

Effects of a fishery closure and prey abundance on seabird diet and breeding success: Implications for strategic fisheries management and seabird conservation

Industrial forage fish fisheries may reduce prey availability affecting diet and breeding success of marine predators. However, evidence for fisheries effects on predator demography remains rare, hindering evaluation of their impact on populations. Using 25 years of data on the commercial lesser sandeel fishery in the north-western North Sea, we evaluated the effectiveness of the closure in safeguarding breeding success of four seabird species - black-legged kittiwake, common guillemot, Atlantic puffin and razorbill. We also tested for effects of a scientific fishery in the closed area on breeding success. We quantified how changes in the diet of chicks for the four seabird species were influenced by the abundance of sandeels and the alternative prey species, European sprat, and the potential prey behavioural disturbance effects of sandeel fishing on the prey. Finally, we examined how changes in chick diet and prey abundance have shaped long-term variation in seabird breeding success. The period of fishery operation was associated with a decline in kittiwake breeding success in colonies with foraging ranges overlapping the closed area, from 52 % of young fledged pre-fishery to 23 % during fishery operation. Breeding success increased by approximately 10 % in the period following fishery closure to 2018. We document wide uncertainty around this increase in breeding success, partly driven by variation in the responses of individual colonies. For guillemot, razorbill and puffin we found no evidence for negative effects of the fishery on breeding success, nor for positive effects arising from its closure. We found no evidence for an impact on breeding success of the scientific fishery. The proportion of sandeel in chick diet was positively associated with breeding success in the four species, albeit with only weak evidence for puffin. Fishing effort was associated with a decreased proportion of sandeel in puffin diet, a lower proportion of the sandeel component of the diet consisting of 0-group in kittiwake, razorbill and puffin, and with decreased kittiwake breeding success. Our findings provide quantitative evidence for how forage fish fisheries may impact seabird demography, highlighting the species-specific nature of responses, and the difficulties in teasing apart drivers amongst ongoing environmental change. Time-area fisheries closures show promise as a tool for positively affecting productivity in some seabird species. However, we identify important caveats around its effectiveness for strategic seabird conservation and aspirations of net gain.

The morphometric, meristic and genetic characteristics of European sprat (Sprattus sprattus) in the Black Sea

The European sprat (Sprattus sprattus) represents the unit stock shared among the Black Sea countries. It has a key role in the Black Sea ecosystem and is determined by its importance from both a commercial and an ecological point of view. Up to now, there are few studies on the meristic, morphometric and genetic characteristics of this species. In this study, the species were specified and studied for meristic, morphometric and genetic characteristics. Mitochondrial gene regions which 16S rRNA and cytochrome c oxidase subunit I (COI), were studied and compared with some of the family Clupeidae species in the National Center for Biotechnology Information (NCBI) and the phylogenetic relationship was examined. A total of 14 haplotypes were determined for the mitochondrial COI gene region and 3 haplotypes were determined for the 16S rRNA gene region. This study will contribute to the sustainable management of this species as well as be a basis for future studies.

ОЦЕНКА СОСТОЯНИЯ ЗАПАСОВ МОРСКИХ ВИДОВ РЫБ ЧЕРНОГО МОРЯ (ВОДЫ РОССИИ) В 2021 Г

Based on the available biological and fisheries data, stock status review for 18 units of the fish species inhabiting the Black Sea and the both Azov and Black Seas is presented. A modified version of the traditional approach to the harvest control rules for the aquatic bioresources of the Azov and Black Sea Fishery Basin is described for the case when they are assessed by the mathematical methods to estimate the current stock biomass and fishing mortality. For 11 stock units, analytical modeling including cohort, production and trend models has been applied. Based on the estimates of biomass and fishing mortality concerning biological reference points, in 2021, the status of six stock units of the marine fish species inhabiting the basin and exploited by the Russian fisheries was identified as increasing or stable (“Black Sea” stock units of the European sprat and European anchovy, “Crimean” stock unit of turbot, “Crimean and Caucasian” stock unit of red mullet, and “Black and Azov Seas” stock units of garfish and rays). Five fishery stock units (“Crimean and Caucasian” of mullets, picarel and Mediterranean horse mackerel, “Black and Azov Seas” of sand smelts, and “Caucasian” of turbot) have shown a decreasing trend in terms of abundance, and for the rest of the investigated fish stock units (“Mediterranean migrant” bluefish, Atlantic bonito and Atlantic mackerel, “Black Sea” whiting, so-iuy mullet and the other marine fish species, “Black and Azov Seas” spiny dogfish), the status has not been determined due to the absence of systematic biological and fishery data.

Diet and trophic interactions of Mediterranean planktivorous fishes

Diet and trophic interactions of seven species of planktivorous fishes: European anchovy Engraulis encrasicolus, European sardine Sardina pilchardus, round sardinella Sardinella aurita, European sprat Sprattus sprattus, red bandfish Cepola macrophthalma, damselfish Chromis chromis and bogue Boops boops were studied in the Bay of Marseille (North-Western Mediterranean Sea) from March to September 2017. Taxonomic composition and size distribution of prey were studied using stomach content analysis, and compared to prey availability determined by continuous zooplankton sampling at a fixed point. Frequently consumed items included copepods, decapod larvae and fish eggs. Comparatively, E. encrasicolus consumed more calanoid copepods (i.e. Centropages spp.), S. pilchardus, S. aurita and S. sprattus consumed more harpacticoid copepods (i.e. Microsetella/Macrosetella spp.), C. macrophthalma consumed more decapod larvae, C. chromis consumed more pteropods and B. boops consumed more benthic polychaetes. Sardina pilchardus consumed the widest diversity of prey. Prey size distribution and average prey size significantly differed among species. The prey–predator size ratio (PPSR) was highest for B. boops and lowest for S. aurita. Carbon and nitrogen stable isotope composition of species overlapped, probably due to the ingestion of particulate organic matter from the same sources at the base of the planktonic food web in the Bay of Marseille. Furthermore, trophic niche overlap supported the hypothesis of potential trophic competition between Engraulidae and Clupeidae.

Trophic ecology of northern gannets Morus bassanus highlights the extent of isotopic niche overlap with other apex predators within the Bay of Biscay

Understanding the linkages within complex and evolving marine food webs is essential to comprehend marine ecosystem structure and dynamics. Carbon (δ13C) and nitrogen (δ15N) stable isotope signatures are recognized to be powerful descriptors of the trophic ecology and trophic relationships within marine communities. Apex predators such as seabirds can influence the structure of communities by predating in lower trophic levels. They also convey information both over a range of spatial and temporal scales due to their high mobility and longevity, respectively. For this reason, here, we studied the trophic ecology of northern gannets and the extent of niche overlap with other apex predators within the Bay of Biscay (North-East Atlantic), a key feeding area for numerous predatory species. Mixing models indicated that northern gannets fed primarily on European anchovy Engraulis encrasicolus and on a mixed group composed of European sardine Sardina pilchardus, European sprat Sprattus sprattus, juvenile hake Merluccius merluccius, Atlantic mackerel Scomber scombrus and Atlantic horse mackerel Trachurus trachurus. Within the apex predator community, the northern gannets trophic niche overlapped the most with common guillemots Uria aalge (15.58%, based on Stable Isotope Bayesian Ellipses (SIBER)) and overlapped to a lesser extent with cetacean species occupying shelf habitats (i.e., the harbour porpoise Phocoena phocoena (9.99%) and the short-beaked common dolphin Delphinus delphis (10.37%)). Overall, the overlap found was moderate indicating trophic similarities and dissimilarities between these species. Information on trophic interactions between co-existing species is necessary for holistic environmental management, particularly in areas where several megafauna species share their foraging grounds with fisheries activity.

The Dynamics of 0-Group Herring Clupea harengus and Sprat Sprattus sprattus Populations Along the Norwegian Skagerrak Coast

Coastal areas are important habitats for early life stages of many fish species. These habitats are used as nursery grounds and can provide a significant contribution to the recruitment of a fish population. In 1919, standardized sampling with a beach seine along the Norwegian Skagerrak coastline was established mainly to target 0-group fish. Here, we focus on Atlantic herring and European sprat to explore whether inter-annual variability in the abundance of these species is indicative of variability in recruitment. We investigated if the abundance of 0-group herring and sprat are affected by environmental factors. Further, the beach seine abundance indices were compared with recruitment estimates of neighboring stocks. There was a clear correlation between herring and sprat abundance in the beach seine samples. While sprat abundance was mainly affected by environmental factors such as temperature and current drift, herring abundance was positively affected by the recruitment of the neighboring stock of western Baltic spring spawners. One plausible explanation could be that sprat recruit to a more local component, while herring of the neighboring stock utilize the Skagerrak coastline as nursery grounds. This study demonstrates the importance of long time series and can provide new insight into the dynamics and structure of multiple fish species.

Habitat suitability models of five keynote Bulgarian Black Sea fish species relative to specific abiotic and biotic factors

Over the past few years, predicting species spatial distributions has been recognized as a powerful tool for studying biological invasions in conservation biology and planning, ecology, and evolutionary biology. Species spatial distribution models (SDMs) are used extensively for assessing the effects of changes in habitat suitability, the impacts of climate change, and the realignment of the existing conservation priorities. SDMs relate known patterns of species occurrences to a specific set of environmental conditions. Accordingly, we have used MaxEnt SDM tool in order to provide habitat suitability models of 5 keynote fish species: European sprat (Sprattus sprattus L.), red mullet (Mullus barbatus, L.), horse mackerel (Trachurus mediterraneus, L.), bluefish (Pomatomus saltatrix, L.) and whiting (Merlangius merlangus, L.), inhabiting the Bulgarian region of the Black Sea. Presence-only (PO) data collected by pelagic surveys performed between 2017 and 2019 was further utilized to link known species occurrence localities with selected abiotic factors, such as surface sea temperature and salinity, dissolved oxygen, and speed of currents. Biotic interactions were also considered for fitting the patterns of habitat suitability models. The SDMs, obtained from the present research study, prove to have satisfactory predictive accuracy to be further implemented for conservation measures and planning, stock management policy-making, or ecological forecasting.

Long-term dynamics of reproductive potential and fishing of European sprat Sprattus sprattus (Linnaeus, 1758) (Pisces: Clupeidae) in the Black Sea

Long-term dynamics of reproductive potential and fishing of European sprat Sprattus sprattus (Linnaeus, 1758) (Pisces: Clupeidae) in the Black Sea

A spatial statistical approach for identifying population structuring of marine fish species: European sprat as a case study

AbstractMany marine fish species are widely distributed over large areas. Failing to acknowledge that such species may be composed of distinct populations may result in overestimation of the stock's true harvest potential. To avoid overexploitation, ways to identify population structuring are therefore needed. In this study, we developed and applied a statistical approach to identify biologically relevant population boundaries for a widely distributed marine fish species, European sprat (Sprattus sprattus). Specifically, we compiled and standardized multiple trawl-survey data sets and used a range of statistical tools to assess whether the current management boundaries adequately account for potential population structuring. Our results demonstrate regional differences in spatial abundance patterns, temporal dynamics and population demographics. These findings are in line with recent genetic studies of sprat, indicating reproductive isolation between the Baltic Sea/Kattegat and a larger cluster containing the North-, Irish-, Celtic Sea, and Bay of Biscay. Since relying on routinely collected survey data, our statistical approach can be a cost-effective complement to population genetic methods for detecting population structuring. These can be used to guide spatial management efforts and ensure sustainable exploitation, especially under climate change and the expected changes in species distributions across current management borders.

Effect of Pre-Treatment on the Quality of Smoked Baltic Sprats

Abstract Baltic sprats (Sprattus sprattus balticus) are a good source of protein, vitamins D3, B12, minerals, and unsaturated fats. In response to consumer demand, various types of fish products of stable quality are available all year round. Pre-treatment with brine containing acetic acid, salt (NaCl), and/or granulated CaCl2 in various concentrations and proportions can be used to stabilise quality. The aim of the study was to evaluate the effect of various pre-treatment methods on smoked Baltic sprat sensory and technological parameters. Prior to smoking, fish was treated in a solution of additives in various proportions for 30 min. Untreated sprats were used as a control sample. The use of pre-treatment allowed reduction of the smoking losses; the combination of NaCl and acetic acid resulted in about 26% smoking loss. If no pre-treatment was applied, the drying losses after 24-hour storage were 1.6%, while using the solution of NaCl and CaCl2 it decreased to 0.3%. Both the pre-treatment method and freezing affected fish pH. The pH of smoked fresh sprats was 6.73 and for smoked frozen sprats, it was 6.38. Sensory testing using the Just About Right (JAR) method demonstrated that the use of acetic acid made smoked fish texture firmer.