Coastal Fish Species Research Articles

Combining population genomics with demographic analyses highlights habitat patchiness and larval dispersal as determinants of connectivity in coastal fish species.

Gene flow shapes spatial genetic structure and the potential for local adaptation. Among marine animals with nonmigratory adults, the presence or absence of a pelagic larval stage is thought to be a key determinant in shaping gene flow and the genetic structure of populations. In addition, the spatial distribution of suitable habitats is expected to influence the distribution of biological populations and their connectivity patterns. We used whole genome sequencing to study demographic history and reduced representation (double‐digest restriction associated DNA) sequencing data to analyse spatial genetic structure in broadnosed pipefish (Syngnathus typhle). Its main habitat is eelgrass beds, which are patchily distributed along the study area in southern Norway. Demographic connectivity among populations was inferred from long‐term (~30‐year) population counts that uncovered a rapid decline in spatial correlations in abundance with distance as short as ~2 km. These findings were contrasted with data for two other fish species that have a pelagic larval stage (corkwing wrasse, Symphodus melops; black goby, Gobius niger). For these latter species, we found wider spatial scales of connectivity and weaker genetic isolation‐by‐distance patterns, except where both species experienced a strong barrier to gene flow, seemingly due to lack of suitable habitat. Our findings verify expectations that a fragmented habitat and absence of a pelagic larval stage promote genetic structure, while presence of a pelagic larvae stage increases demographic connectivity and gene flow, except perhaps over extensive habitat gaps.

Ingested Microplastics in 18 Local Fish Species from the Northwestern Mediterranean Sea

Plastic waste and its fragments (microplastics, <5 mm) are a global, persistent, and ubiquitous threat for land and marine ecosystems. We have investigated the occurrence and composition of microplastics within 18 coastal fish species of the northwestern Mediterranean Sea. Digestive tracts were digested using hydrogen peroxide, and residues were observed under a stereo-microscope. Suspected microplastics were analyzed with a Fourier Transform InfraRed (FTIR) spectrometer to confirm its plastic nature and to identify the polymer type. A rigorous blank control and FTIR correction was applied, leading to the removal of 78% of the initially sorted and suspected particles. Corrected concentrations range from 0.00 to 5.15 items per fish, a result within the same range than this has been reported for other coastal species previously investigated in this area. Fibers, made of polyester (PES), polyamide (PA), acrylic (A) and polypropylene (PP), largely dominate the microplastic shapes (91%). A single driving force could not be identified, but several species traits (morphology, feeding, and habitat) may influence the number of ingested microplastics.

Assessment of the Effects of Salt and Salicornia herbacea L. on Physiochemical, Nutritional, and Quality Parameters for Extending the Shelf-Life of Semi-Dried Mullets (Chelon haematocheilus).

Mullet, a coastal fish species, is commonly used as a salted dried fish in many countries, including Korea, Japan, and the southeastern United States. The purpose of this investigation was to develop high-quality products of salted semi-dried mullet (SSDM) using natural salt and Salicornia herbacea L. (SAL). The antioxidant activity of SAL was investigated by in vitro studies. The physicochemical and nutritional characteristics of fresh mullet (FM), salted control (SSDM-CON), and SAL-treated (SSDM-SAL) mullet groups were analyzed. The moisture, ash, and crude protein contents were significantly increased in the SSDM-SAL group, whereas the salinity was decreased when compared with the SSDM-CON group. Lipid oxidation occurred in the FM and SSDM groups, as indicated by the increase in peroxide (PV), acid (AV), and thiobarbituric acid reactive substance (TBARS) values during the storage period. The protein pattern on the sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed similarities between the groups, while the amino acid and fatty acid contents also varied in the FM and SSDM groups depending on their processing methods. Initially, the total bacterial count was significantly higher in the SSDM groups than in the FM group. However, the SSDM-SAL group had a markedly lower total bacteria count than the FM and SSDM-CON groups during 21 days of refrigerated storage. This result indicates that SAL treatment can improve mullet’s safety from microorganisms, includes beneficial biochemical parameters, and can extend their shelf-life through refrigerated storage.

Bioluminescent bacterial flora of Nigerian coastal fish species

The scarcity of studies on bioluminescent bacteria in fish species along the coastal and marine environment of Nigeria prompted the assessment of abundance of bioluminescent bacteria and possible isolation on three common coastal fish species ( Drepane africana , Sardinella maderensis and Mugil cephalus ) displaying luminescence. The population of the luminescent bacteria among the three fish species ranged from 2.95×10 5 to 6.68×10 6 cfu ml -1 and the corresponding percentage to the heterotrophic bacteria was between 0.01 and 0.34 %. The surface water had 2.00×10 5 cfu ml -1 with 0.20 % ratio to heterotrophic bacteria. The predominant luminescent bacteria observed were gram-negative short rod. Further study of these bacteria showed that growth and light emission occurred concurrently without the exhibition of lag phase; however, maximum luminescence was observed at mid-exponential growth phase suggesting quorum sensing phenomenon. The 16S rRNA gene sequence showed 92.81 % homology to Vibrio campbelli , Vibrio harveyi and Vibrio rotiferianus . This study highlights the occurrence of bioluminescent bacteria in skin of tropical coastal fish species in Nigerian coastal waters and also serves as a fundamental basis for future studies on the biotechnological application of this unique characteristics.

Seasonal and spatial variability of Atlanto-Iberian pelagic fish diet with estimates of intraguild predation

The diets of 3 of the most abundant coastal pelagic fish species in the eastern Atlantic (sardine, anchovy and Atlantic chub mackerel) were investigated, including seasonal, geographical and ontogenetic variability of the diets. We also estimated the impact of cannibalism and intraguild predation on egg mortality, and a different method to evaluate egg mortality is proposed taking the spatial overlap of predators and eggs into account. Diet overlap occurred between the 3 pelagic species, which derive most of their dietary carbon from mesozooplankton prey. However, calanoid copepods were mostly important for anchovy and sardine, whereas the diet of the Atlantic chub mackerel also included crustacean eggs, nauplii, small copepodites and larger prey such as decapods. Sardine was the main predator of fish eggs (90% of all identified eggs), followed by Atlantic chub mackerel (8%) and anchovy (2%). Cannibalism by anchovies and sardines on their eggs was low (<10% of spawned eggs) for all areas and seasons. The impact of sardine predation on anchovy egg mortality was high (71% of the anchovy eggs spawned per day during the spring off northwestern Iberia) and may explain why anchovy abundance has only peaked in recent years, when sardine abundance was at its lowest level, highlighting the importance of taking an ecosystem approach to fisheries management into account. However, species-specific data of gastric evacuation rates and feeding durations are needed to obtain more accurate estimates of the impact of cannibalism and intraguild predation on egg mortality.

Environmental influences on the ichthyoplankton in hypersaline estuaries located in a Semiarid Northeastern Brazilian coast

ABSTRACT Hypersaline estuaries are commonly found in the Semiarid Northeast Brazilian coast. However, the utilization of these estuaries by early life stages of fishes is less well documented. This study aimed to evaluate the effects of environmental factors on the ichthyoplankton, and to describe their spatial and temporal variation in two estuaries (Tubarão and Casqueira). The sampling were diurnally in four excursions carried out during two dry-season months (November and December 2017) and two rainy-season months (May and July 2018). A total of 423 larvae representing 30 species (14 families) and 2,762 eggs (five families) were collected. Although the community structures were similar in both estuaries, there was strong seasonal variation, with higher abundances observed during the dry season. Low rainfall was the primary environmental driver affecting ichthyoplankton in both estuaries. Other environmental factors, such as depth, water temperature, and channel width, were also predictor variables for the distribution of eggs and larvae. The ichthyoplankton was dominated by marine estuarine-dependent species in both estuaries, accounting for 76% of individuals. The presence of the early life stages of typically marine species suggests that hypersaline environments provide important nursery areas and play an essential role for some coastal fish species.

Larval Fish Assemblage Structure at Coastal Fronts and the Influence of Environmental Variability

Within the coastal zone, oceanographic features, such as fronts, can have major effects on the abundance and distribution of larval fish. We investigated the effects of fronts on larval fish assemblages by jointly collecting physical (ADCP and CTD) and biological (larvae) data in the nearshore waters of the south coast of South Africa, on four separate neap-tide occasions. Accumulation of fish larvae at predominantly internal wave-associated fronts was observed, with higher larval densities inshore of and within the front than farther offshore. On each occasion, larvae of coastal species with pelagic eggs (Mugillidae and Sparidae) were numerically dominant at the front itself, while inshore of the front, larvae of coastal species with benthic eggs (Gobiesocidae and Gobiidae) were more abundant. Offshore catches mainly comprised Engraulidae (pelagic species with pelagic eggs) larvae, which were generally restricted to the bottom, where current velocities were onshore on each occasion. On the occasion when fast (>100 cm/s) currents prevailed, however, accumulation of the larvae of coastal species occurred offshore of the front, and larvae were mixed throughout the water column. Thus, larval occurrence at these coastal frontal systems was strongly affected by the degree of mixing by currents, which on most occasions resulted in onshore retention. The results underline the importance of frontal systems in determining the nearshore distributions of fish larvae, particularly by retaining coastal fish species in the inshore region. The environmental variability observed at these frontal systems has potential implications for larval connectivity of fish populations.

Pushed to the edge: Environmental factors drive ecological responses of Aphanius fasciatus when in sympatry with invasive Gambusia holbrooki

Abstract Interspecific competition may be particularly exacerbated when occurring between native and invasive alien species, with environmental conditions affecting drivers of natural selection and shaping spatio‐temporal dynamics of animal communities. The effects of invaders are particularly evident in aquatic ecosystems with delicate and complex balances, such as Mediterranean coastal wetlands, characterized by unpredictable water flows and variable reserves. Understanding how native species respond to human‐induced biological invasions is of paramount importance for planning management measures aiming at conservation purposes. This study investigated whether the occurrence of a competing invader species resulted in changes in the ecological adaptations of a native species by comparing two coastal wetland fish species: the invasive eastern mosquitofish Gambusia holbrooki and the native Mediterranean killifish Aphanius fasciatus of conservation concern. The hypothesis was tested by sampling fishes at a coastal Ramsar site in central Italy, over 2 years. Generalized linear mixed models were used to examine the occurrence of killifish in relation to water parameters and the presence of its putative competitor. The aim was to determine whether salinity, temperature, and water depth influenced the presence and abundance of killifish when in sympatry with mosquitofish. Both the probability of presence and abundance of killifish increased with water salinity, but this increase was stronger when mosquitofish was present. Increasing water temperature and water depth were associated with a higher probability of presence and abundance of killifish respectively, although the effect of water depth was small. Both salinity and the presence of the invader acted synergistically in characterizing and shaping the population structure of the native species. Living in the most extreme and stressed environments, the killifish is potentially at higher risk of extinction. These results highlight the importance of considering the interplay between multiple abiotic stressors combined with comparative data between invasive and native species as increasingly critical to aid in conservation efforts.

Species on the move around the Australian coastline: A continental-scale review of climate-driven species redistribution in marine systems.

Climate‐driven changes in the distribution of species are a pervasive and accelerating impact of climate change, and despite increasing research effort in this rapidly emerging field, much remains unknown or poorly understood. We lack a holistic understanding of patterns and processes at local, regional and global scales, with detailed explorations of range shifts in the southern hemisphere particularly under‐represented. Australian waters encompass the world's third largest marine jurisdiction, extending from tropical to sub‐Antarctic climate zones, and have waters warming at rates twice the global average in the north and two to four times in the south. Here, we report the results of a multi‐taxon continent‐wide review describing observed and predicted species redistribution around the Australian coastline, and highlight critical gaps in knowledge impeding our understanding of, and response to, these considerable changes. Since range shifts were first reported in the region in 2003, 198 species from nine Phyla have been documented shifting their distribution, 87.3% of which are shifting poleward. However, there is little standardization of methods or metrics reported in observed or predicted shifts, and both are hindered by a lack of baseline data. Our results demonstrate the importance of historical data sets and underwater visual surveys, and also highlight that approximately one‐fifth of studies incorporated citizen science. These findings emphasize the important role the public has had, and can continue to play, in understanding the impact of climate change. Most documented shifts are of coastal fish species in sub‐tropical and temperate systems, while tropical systems in general were poorly explored. Moreover, most distributional changes are only described at the poleward boundary, with few studies considering changes at the warmer, equatorward range limit. Through identifying knowledge gaps and research limitations, this review highlights future opportunities for strategic research effort to improve the representation of Australian marine species and systems in climate‐impact research.

The Atlantic salmon's stress- and immune-related transcriptional responses to moderate hypoxia, an incremental temperature increase, and these challenges combined.

The marine environment is predicted to become warmer, and more hypoxic, and these conditions may negatively impact the health and survival of coastal fish species, including wild and farmed Atlantic salmon (Salmo salar). Thus, we examined how: (1) moderate hypoxia (∼70% air saturation) at 12°C for 3 weeks; (2) an incremental temperature increase from 12°C to 20°C (at 1°C week−1) followed by 4 weeks at 20°C; and (3) treatment “2” combined with moderate hypoxia affected transcript expression in the liver of post-smolts as compared to control conditions (normoxia, 12°C). Specifically, we assessed the expression of 45 genes related to the heat shock response, oxidative stress, apoptosis, metabolism and immunity using a high-throughput qPCR approach (Fluidigm Biomark™ HD). The expression profiles of 27 “stress”-related genes indicated that: (i) moderate hypoxia affected the expression of several stress genes at 12°C; (ii) their expression was impacted by 16°C under normoxic conditions, and this effect increased until 20°C; (iii) the effects of moderate hypoxia were not additive to those at temperatures above 16°C; and (iv) long-term (4 weeks) exposure to 20°C, with or without hypoxia, resulted in a limited acclimatory response. In contrast, the expression of 15 immune-related genes was not greatly affected until temperatures reached 20°C, and this effect was particularly evident in fish exposed to the added challenge of hypoxia. These results provide valuable information on how these two important environmental factors affect the “stress” physiology and immunology of Atlantic salmon, and we identify genes that may be useful as hypoxia and/or temperature biomarkers in salmonids and other fishes.

Using growth rates and otolith shape to identify the population structure of Umbrina canosai (Sciaenidae) from the Southwestern Atlantic

ABSTRACT Identifying populations and establishing the connectivity between neighbouring stocks are central issues for the assessment and management of coastal marine fish species. In this paper, we analysed the population structure of the demersal sciaenid argentine croaker Umbrina canosai, endemic in the warm, temperate southwestern Atantic between southeastern Brazil (SE) and Argentina, by combining two phenotypic techniques: otolith shape analysis and fish growth rate. Three otolith morphotypes were consistently identified, one in the northern latitudinal range in SE, and two in the southern range of the species from southern Brazil to Argentina. Two stocks with differences in growth rate were identified, one with a significantly smaller asymptotic length in the northern range (L ∞ = 340.08; k = 0.267; t0 = −2.177) and the second in the southern range (L ∞ = 425.08; k = 0.236; t0 = −2.46), where no growth differences were observed between fishes with the two otolith morphotypes. Although genetically U. canosai can be considered to form a single panmictic population, growth and otolith shape indicate that there are two different stocks, one in southeastern Brazil and another in the southern distribution, confirming previous parasitological studies. The difference in otolith morphotypes in the southern range suggests that two subpopulations share the same reproductive grounds, although probably feed in different locations.

Length-weight relationships for the fifty littoral and coastal marine fish species from the Eastern Adriatic Sea

The length–weight relationship parameters are reported for the fifty littoral and coastal marine fish species from the Eastern Adriatic. Captures were made between the years 2004 and 2017 during sport fishing competitions. The parameters a and b of the equation W = aLb were estimated. The b values ranged from 2.1972 for Spicara smaris (Linnaeus, 1758) to 3.7044 for Salaria pavo (Risso, 1810). The L-W relation for Scyliorhinus stellaris (Linnaeus, 1758), Gobius bucchichi Steindachner 1870, Gobius geniporus Valenciennes 1837 and Lipophrys trigloides (Valenciennes, 1836) are not available in FishBase and presents new data for these species. For some other species, such as Labrus mixtus Linnaeus 1758, there are only two relationships, but none from the Mediterranean, for Gobius paganellus Linnaeus 1758 only four relationships and none from Central and Eastern Mediterranean, while for Labrus merula Linnaeus 1758, Symphodus mediterraneus (Linnaeus, 1758), Symphodus roissali (Risso, 1810), Gobius cobitis Pallas 1814, Gobius cruentatus Gmelin 1789, Gobius niger Linnaeus 1758, Parablennius gatorugine (Linnaeus, 1758), Parablennius sanguinolentus (Pallas, 1814), Salaria pavo (Risso, 1810), and Bothus podas (Delaroche, 1809) very low number of relationships are presented and none from the Adriatic Sea.

The biodiversity of fishes at the Islas Marías Biosphere Reserve, Mexico, as determined by baited remote underwater video

The Islas Marías Biosphere Reserve, made up of 4 islands in Pacific waters off central Mexico, supports a large diversity of marine life. However, scientific research was restricted for decades by the occupation of Isla María Madre by the Federal Penitentiary Colony of Mexico from 1905 to 2019. Aside from a list of coastal fish species published in 2011, little has been published about the fish biodiversity in the area. While the limited access to the archipelago may have acted as a de-facto marine reserve, there is evidence that fishing continued both legally for the benefit of the colony and illegally by trespassing vessels. In order to establish baseline ecological data for future conservation planning, we used baited remote underwater video (BRUV) surveys at all 4 islands during 3 expeditions to the archipelago in 2018. A total of 131 BRUV surveys representing ~150 h of footage were analyzed to create the most current compilation of species and abundance data on coastal marine fishes at Islas Marías. Ninety-nine species were identified, 3 of which were additions to the previous assessment. We found strong separation of fish communities based on both habitat and depth, and an association between hard-bottom habitats and high biodiversity of reef fishes. With the declaration of Islas Marías as a natural reserve and relocation of the prison in 2019, there is an opportunity for the reserve to become a priority area for marine conservation on the Pacific coast of Mexico. Spatial analyses of fish biodiversity at Isla María Cleofas can help develop sustainable management strategies at a time when the governmental jurisdiction of the iconic archipelago is uncertain.

The bastard grunt Pomadasys incisus (Bowdich, 1825) (Teleostei: Haemulidae) in Cyprus (eastern Mediterranean Sea) - a late arrival or just a neglected species?

Pomadasys incisus is a thermophilous coastal subtropical fish species belonging to the family Haemulidae. Originally described from Gambia, this species is widely distributed in the Eastern Atlantic from Galicia to South Africa. It has also been recorded in the Mediterranean Sea since 1840, presumably expanding its distribution in the next decades, although the species could have been already present in the basin, but simply overlooked until the mid XIX century. In this study, we first record P. incisus from Cyprus (eastern Mediterranean Sea), based on two opportunistic observations obtained through a citizen-science project and review the distribution of this species in the Mediterranean Sea. The present sighting raises the question on whether this species is a late arrival in the country or its presence has just been neglected until now. Based on present data, the most likely hypothesis is the latter one, with P. incisus occurring in low densities and being overlooked due to the absence of field studies. Whatever is true, some intrinsic or extrinsic factors may have played a role in limiting its spread or wide establishment in the above-mentioned country.

Novel deep-water spawning patterns of bonefish (Albula vulpes), a shallow water fish

Coastal marine fishes that form spawning aggregations most commonly exhibit a two-point movement pattern, with locations separated by migration: home range to spawning aggregation site and return to home range. However, the bonefish, Albula vulpes, partakes in a unique three-point spawning migration. Bonefish migrate up to 80 km from shallow water home flats to form nearshore pre-spawning aggregations (PSA) before moving offshore to spawn. Although these broad patterns have previously been documented, details of the offshore spawning-associated diving behavior have yet to be rigorously examined. Using active acoustic telemetry and sonar data in 2019 in Abaco, The Bahamas, we provide a complete account of bonefish offshore spawning movements and novel deep diving behavior to 137.9 m. Bonefish were continuously observed at depths ≥ 100 m for 2 h; a time period that included multiple depth changes and culminated in a spawning ascent to 67.3 m at 0.57 m s−1. These new data on bonefish offshore movements and deep dives, coupled with CTD data, suggest that bonefish actively spawn at pycnoclines and thermoclines. Two previous tracking attempts (2013, 2018) at this location reflect spatiotemporal plasticity in spawning, a behavior counter to other aggregation forming fishes. This is the first detailed documentation of such deep spawning for a shallow water coastal fish species. The ecological motivation for diving to the deepest depths remains speculative. Future work must examine the dynamic relationship between bonefish diving behavior, spawning site selection, and oceanographic features.

Estimating Shifts in Phenology and Habitat Use of Cobia in Chesapeake Bay Under Climate Change

Cobia (Rachycentron canadum) is a large coastal pelagic fish species that represents an important fishery in many coastal Atlantic states of the U.S. They are heavily fished in Virginia when they migrate into Chesapeake Bay during the summer to spawn and feed. These coastal habitats have been subjected to warming and increased hypoxia which in turn could impact the timing of migration and the habitat suitability of Chesapeake Bay. With conditions expected to worsen, we project current and future habitat suitability of Chesapeake Bay for cobia and predict changes in their arrival and departure times as conditions shift. To do this we developed a depth integrated habitat model from archival tagging and physiology data from cobia that used Chesapeake Bay, and applied the model to contemporary and future temperature and oxygen output from a coupled hydrodynamic-biogeochemical model of Chesapeake Bay. We found that arrival occurs earlier and departure time occurs later when temperatures are warmer and that by mid- and end-of-century cobia may spend on average up to 30 and 65 more days, respectively, in Chesapeake Bay. By mid-century we do not expect habitat suitability to change substantially for cobia, but by end-of-century we project it will significantly decline and shift closer to the mouth of Chesapeake Bay. Our study provides evidence that cobia will have the capacity to withstand near term impacts of climate change, but that their migration phenology varies from year to year with changing temperatures. These findings emphasize the need to incorporate the relationship between fishes and their environment into how fisheries are managed. This information can also help guide managers when deciding the timing and allocation of a fishery.

A Bayesian approach for assessing the boundary between desirable and undesirable environmental status – An example from a coastal fish indicator in the Baltic Sea

Ecological indicator approaches typically compare the prevailing state of an ecosystem component to a reference state reflecting good environmental conditions, i.e. the desirable state. However, defining the reference state is challenging due to a wide range of uncertainties related to natural variability and measurement error in data, as well as ecological understanding. This study propose a novel probabilistic approach combining historical monitoring data and ecological understanding to estimate the uncertainty associated with the boundary value of an ecological indicator between good and poor environmental states. Bayesian inference is used to estimate the epistemic uncertainty about the true state of an indicator variable during an historical reference period. This approach replaces the traditional boundary value with probability distribution, indicating the uncertainty about the boundary between environmental states providing a transparent safety margin associated with the risk of misclassification of the indicator’s state. The approach is demonstrated by applying it to a time-series of an ecological status indicator, ‘Abundance of coastal key fish species’, included in HELCOM’s Baltic Sea regional status assessment. We suggest that acknowledgement of the uncertainty behind the final classification leads to more transparent and better-informed decision-making processes.

Metabolic and physiological responses of a coastal fish in highly and lightly impacted habitats

Abstract Coastal and estuarine zones are used by fish as nursery, spawning and feeding grounds. However, these essential habitats are characterized by the presence of both natural and anthropogenic stressors that may represent potential threats for the wellbeing of aquatic organisms, particularly fish. The main objective of this study was to evaluate and understand the effects of environmental stressors, both natural and anthropogenic, on coastal fish species using Ramnogaster arcuata as bioindicator. Fish were captured in two zones with different human activity levels: a highly impacted zone in Bahia Blanca Estuary (BBE) and a lightly impacted zone in the adjacent coastal zone (ACZ). Various indicators were used to determine fish responses to environmental stress. Main differences found between fishes from the two zones were in the condition index, trophic ecology (including feeding activity and diet composition) and liver metabolic biomarkers (ALT/AST enzymes, protein levels and lipid peroxidation). On the other hand, metal concentration levels analyzed in muscle did not show important differences between both environments. Physiological responses of R. arcuata from both zones were strongly correlated with natural stressors.

Extending full protection inside existing marine protected areas, or reducing fishing effort outside, can reconcile conservation and fisheries goals

Abstract Most fish stocks world‐wide are fished at maximum sustainable yield (MSY) or overfished, as many fisheries management strategies have failed to achieve sustainable fishing. Identifying effective fisheries management strategies has now become urgent. Here, we developed a spatially explicit metapopulation model accounting for population connectivity in the north‐western Mediterranean Sea, and parameterized it for three ecologically and economically important coastal fish species: the white seabream Diplodus sargus, the two‐banded seabream Diplodus vulgaris and the dusky grouper Epinephelus marginatus. We used the model to assess how stock biomass and catches respond to changes in fishing mortality rate (F) and in the size of fully protected areas within the existing system of multiple‐use marine protected areas (MPAs). For each species, we estimated MSY and the corresponding values of stock biomass (BMSY) and fishing mortality rate (FMSY), providing crucial reference points for the assessment of fisheries management. Diplodus sargus is currently in low overfishing, while D. vulgaris and E. marginatus are in high overfishing. Stock recovery to BMSY for the last two species requires a reduction of current F around 50%. This would guarantee an increase in both stock biomass (around 50% and 75% for D. vulgaris and E. marginatus respectively) and catch (around 15% and 30%) after a transient time of ~15–30 years. Alternatively, doubling the size of fully protected areas over fishable areas within the existing network of MPAs would lead to positive conservation effects for all three species without substantially affecting the overall productivity of the fishery and the total economic value of the catch. Synthesis and applications. We provide the first assessment of stock status for three coastal species in the north‐western Mediterranean and evaluate the ecological and fisheries outcomes of different management strategies. Extending full protection inside existing multiple‐use marine protected areas or reducing fishing effort outside can deliver both conservation and fisheries benefits.

Effects of salinity on the growth, plasma ion concentrations, osmoregulation, non-specific immunity, and intestinal microbiota of the yellow drum (Nibea albiflora)

The yellow drum (Nibea albiflora) is a coastal fish species that is intensively farmed in China. The aquaculture of this species is mainly restricted to coastal ponds and net cages in areas that may experience a wide variation in salinity due to rainfall or freshwater input. However, our knowledge regarding the impacts of salinity on the growth and health of yellow drum is limited. In this study, we evaluated salinity tolerance of yellow drum based on their survivals at various salinity treatments in a 7-day experiment, and investigated the effects of salinity on the growth performance, blood ion concentrations, Na+-K+-ATPase and non-specific immune enzyme activities, and intestinal microbiota composition of this species in a 7-week experiment. The median lethal time (LT50) revealed that yellow drum reared in water with salinities ranging from 0 to 60 parts per thousand (ppt) survived within a salinity range of 2 to 45 ppt and that large-sized fish (body length = 25.70 ± 0.51 cm) showed a higher salinity tolerance than small-sized fish (body length = 9.52 ± 0.74 cm). Among juvenile fish (small size) maintained for 7 weeks in water with salinities of 6, 12, 18, 30, and 42 ppt, we observed that growth was restricted only at 42 ppt. Although the parameters measured in the blood ion concentrations and activities of Na+-K+-ATPase, antioxidant enzymes, and immunomodulatory enzymes (alkaline phosphatase and acid phosphatase) were mainly non-significant among the fishes in the 6, 12, 18, and 30 ppt groups, in most instances, these parameters were significantly different from those in the fish from the 42 ppt group. This indicates that high salinity would probably represent a stress factor for the yellow drum. Comparison of the intestinal microbiota composition among fish in the 6, 30, and 42 ppt groups revealed that the composition was altered by the salinity level. Notably, the relative abundance of several probiotic taxa that can promote the growth and enhance the immunity of fish was found to be relatively higher in the 6 and 30 ppt groups. However, the abundance of Vibrio species, which are potentially detrimental to fish health, was relatively higher in the 42 ppt group. The findings of this study will enable us to gain a more comprehensive understanding of the effects of salinity on the growth and health of yellow drum and contribute to improvements in the aquaculture of this species.