Cross‐amplification of 10 new isolated polymorphic microsatellite loci for red mullet (Mullus barbatus) in striped red mullet (Mullus surmuletus)

Ten polymorphic dinucleotide microsatellite loci were isolated and characterized for the red mullet (Mullus barbatus). Allele variability was tested on both the red mullet and its congener the striped red mullet (Mullus surmuletus). Characterization of 30 individuals of both species from the western Mediterranean showed moderate to high allelic diversity ranging from two to 26 alleles per locus (mean 10.9). Three loci showed departures from Hardy–Weinberg proportions. No evidence of significant association between genotypes at pairs of loci was observed. These polymorphic loci could be suitable for population genetic assessments of both species.     

Exploitation patterns of the European hake Merluccius merluccius, red mullet Mullus barbatus and striped red mullet Mullus surmuletus in the western Mediterranean

The exploitation patterns of three target species ( Merluccius merluccius , L. 1758 , Mullus barbatus , L. 1758, Mullus surmuletus , L. 1758) of the western Mediterranean demersal fisheries were compared. The study was carried out in five ports along the Italian and Spanish coasts. These three species are fished simultaneously or sequentially by a number of gears, their use during the year being different depending on the area. The trawl catches dominated the landings, both in number and weight, but varied greatly during the year. The size ranges of specimens in the catches were in their major part different among the types of gear. Artisanal methods (gillnet and long line for M. merluccius , trammel net for Mullus spp.), used seasonally, contributed primarily to landings of larger, adult specimens, whereas trawl catches consisted mainly of smaller sized individuals, recently recruited to the fishery. In M. merluccius, individuals of less than 20 cm total length accounted for 80 to 95% of the annual catch in numbers, and between 15 and 60% of the catch in weight, depending on the port. This situation indicates a substantial over-exploitation and a high risk of long-term unsustainability in stock development and production.     

Aggregation dynamics and foraging behaviour of striped red mullet Mullus surmuletus in the western Mediterranean Sea

Habitat‐related heterogeneity of striped red mullet Mullus surmuletus heterospecific foraging assemblages was examined off the coast of Spain. Video‐based focal‐follows conducted on 122 M. surmuletus assemblages (446 total individuals) revealed an array of attendant species (n = 7) with composition linked to benthic habitat complexity; bare sandy substrata were characterized by homospecific groups of M. surmuletus, while habitats with rock and vegetation attracted a variety of scrounging labrids and sparids. Although the nature of the relationship between M. surmuletus and attendants requires further exploration, the present study indicates that substratum composition can be a driving factor explaining the dynamics of this heterospecific assemblage.     

Morphological variability of the shape of striped red mullet Mullus surmuletus in relation to stock discrimination between the Bay of Biscay and the eastern English Channel

Truss analysis and length measurements were made on 168 striped red mullet Mullus surmuletus. Multivariate statistical analyses with principal component analysis and partial redundancy analysis (pRDA) were used on these measurements to evaluate the influence of maturity, sex and geographical area distribution on body shape. Truss measurements were important to quantify and discriminate changing body shape, presumably due to changing environmental conditions. Sexual dimorphism was not observed and juveniles could be distinguished from adults based on their body shape. More importantly, M. surmuletus occurring in different geographical areas could be differentiated using this method. Based on pRDA, a significant difference of head morphological dimensions was observed between populations occurring in the eastern English Channel and those occurring in the Bay of Biscay, suggesting that fish from these areas could represent two subpopulations.     

Oocytes development,maturity classification,maturity size and spawning season of the red mullet (Mullus barbatus barbatus Linnaeus, 1758)

The present study was designed to identify maturity of female red mullet, Mullus barbatus barbatus, using microscopic criteria, offering an accurate determination of the ovarian cycle and estimation of maturity size. Histological analysis of 499 females from 13 monthly samplings was applied (Thermaikos Gulf, N. Aegean Sea, Greece). Oocyte development was divided into five stages, with a mean oocyte size range from 56 to 363 μm in diameter. Ovarian maturity was defined by the maturation stage of the most advanced oocytes and divided into four phases. By using the monthly changes in the percentage frequency of ovarian phases, the ovarian cycle of M. barbatus was divided into three periods: a long period of early oogenesis (November to February), a short period of vitellogenesis (February to April) and a spawning period from April through June with peak activity in May. Both gonadosomatic (up to 7.5%) and hepatosomatic indices (up to 2%) can be used together to predict the spawning period. Red mullet should be classified as a multiple spawning species. Females reached 50% maturity (Lm₅₀) at 11.4 cm and 95% maturity (Lm₉₅) at 15.5 cm TL. The Lm₅₀ values for female red mullet populations across the Mediterranean Sea tended to show differences ranging from 11 to 14.4 cm FL or 11.4–14 cm TL. The current European Union fisheries management plan stipulates a minimum landing size (MLS) of 11 cm TL for Mullidae spp. fisheries in the Mediterranean. This MLS is at the lower part of the Lm₅₀ range, thus allowing an extensive removal of immature juveniles. A revision of this MLS value is recommended to help ensure that red mullet stocks remain within safe biological limits.     

Sexual cycle and seasonal changes in the ovary of the red mullet, Mullus surmuletus, from the southern coast of Brittany

The reproductive cycle of the red mullet is described on a macroscopic scale in terms of the GSI, HSI and K , and on a microscopic scale in terms of histological changes in the ovary and changes in the oocyte size frequency distribution. On the southern coast of Brittany the red mullet breeds in May and June. During oogenesis, the previtellogenic period lasts 6 months and the secondary phase of vitellogenesis no more than 3 months. When spawning commences the process of vitellogenesis ceases and up to 20% of the vitellogenic oocytes become atretic. Prior to spawning a single batch of oocytes can be seen to be entering secondary vitellogenesis. During the immediate prespawning and spawning periods the existing vitellogenic oocytes mature but there is no recruitment from the stock of previteilogenic oocytes. This results in a gap or hiatus in the oocyte size frequency distribution between previtellogenic and vitellogenic oocytes within which there are very few resting or maturing oocytes. The red mullet appears to be a determinate spawner, in which egg loss through atresia considerably reduces the potential fecundity.     

The effects of sex and season on the metal levels and proximate composition of red mullet (Mullus barbatus Linnaeus 1758) caught from the Middle Black Sea

The effects of seasonal and sexual differences on the levels of macro, trace element, and toxic metal levels in Mullus barbatus were investigated using the ICP-MS. The quantity relationships of macro elements were found as K>P>Na>Ca>Mg for male, P>K>Na>Ca>Mg in female; the quantity relationships of trace elements were determined as Fe>Zn>Mn>Mo>Se>Cu>Ni>Co in male, Fe>Zn>Mn>Se>Cu>Ni>Mo>Co in female; and the quantity relationship of toxic elements were found as As>Pb>Cd in both male and female. Macro, trace, and toxic metal levels showed no significant differences (p > .05) in terms of sexuality, but demonstrated seasonal differences (p > .05). Overall, the highest level of macro elements was determined in the autumn, while the high level of trace elements was measured in the winter. The As, Cd, and Pb levels in the muscle tissue of red mullet fish were higher than acceptable limits. However, when the Estimated Daily Intake (EDI) and Estimated Weekly Intake (EWI) of both toxic metals are considered, they appear to be below acceptable limits. As a result, it was determined that the red mullet had been contaminated with toxic metals (Cd and Pb) but their levels according to EDI and EWI were below the limit.     

Parasites as fish population tags and pseudoreplication problems: the case of striped red mullet Mullus surmuletus in the Spanish Mediterranean

Studies of parasites as fish population tags often apply a single round of sampling to identify potential stocks or predict harvest localities. However, the lack of replication generates pseudoreplication, implicitly assuming that infection levels are more similar between samples from the same locality than between samples from different localities. We evaluated this assumption in the case of the striped red mullet Mullus surmuletus in three localities of the Spanish Mediterranean separated by c. 300 km. Samples of 25 fish of similar size were collected in each locality in the summer and autumn of two consecutive years. Prevalence and abundance of three long-lived parasite taxa differed significantly among localities, indicating their potential as stock indicators. However, a cluster analysis (for prevalence) and a MANOVA (for abundance) indicated strong inter-sample variability, even within the same locality, with poor spatial segregation among samples. A linear discriminant analysis (LDA) based on the abundance of 17 parasite taxa correctly assigned over 80% of fish to their locality, and 95% bootstrap confidence intervals of percent classified fish per locality were narrow, indicating good and stable predictive power. However, when a LDA based on data from the first year was used to predict the locality of fish from the second year, predictive power dropped drastically (46% of correct allocation). Overall, we interpret that parasite communities of mullets change at a much lower spatial scale than that adopted in this study. This finding strongly suggests the need for proper replication to make reliable inferences about stock structure in fish populations based on parasitological data.     

Biology of red mullet,Mullus barbatus (L. 1758), in the Gulf of Castellammare (NW Sicily,Mediterranean Sea) subject to a trawling ban

Under‐or non‐exploited areas are useful to aid in evaluating the potential productivity of fish stocks for sustainable fisheries. The Gulf of Castellammare (NW Sicily), where trawling has been banned since 1990, is a good site to study the biology and dynamics of low impacted fish populations. A total of 661 (595 female and 66 male) specimens of red mullet Mullus barbatus (95–245 mm total length, TL) obtained by monthly sampling from trammel net artisanal fishery, was collected in the Gulf of Castellammare from April 2006 to June 2007. Mature females occurred from April to September, with a peak in May. The mean Gonado‐somatic index (GSI) also showed a May peak for both sexes. From Sagittae (642) readings the age structure ranged from age class I to VII in females and I to V in males. Female growth parameters, estimated according to the classic von Bertalanffy model, were: L_∞ = 221.2 ± 11.51 mm standard error (SE), k_y^?1 = 0.38 ± 0.09 SE, t₀y = ?0.94 ± 0.38 SE. The growth performance index (ø’ = 2.27) was included in the range of values obtained by hard structure readings in the Central Mediterranean. Natural mortality (M_y^?1) of females estimated by different methods ranged between 0.62 and 0.87 (mean value = 0.71 ± 0.06 SE).     

The reproductive biology of the horse mackerel Trachurus trachurs (L.) in the North Sea and English Channel

In the horse mackerel the gametes develop asynchronously and are released in batches. The maturity cycle is characterized by a rapid post-spawning recovery period and a relatively long period of oocyte maturation. Mean gonad weight reached a peak in June and intraovarian hyaline oocytes occurred from May to August. Determination of fecundity was complicated by resorption of oocytes both before and after spawning, and by the fact that resting and developing oocytes were not clearly separated by size. An estimate of'potential fecundity'was obtained by a combination of histology and oocyte measurement. Plankton surveys showed that a major spawning area exists in the Southern Bight of the North Sea, with eggs occurring from May to late August. An estimate of annual egg production was combined with the fecundity data to give an estimate of stock size of about 500 000 tons.     

The influence of feeding behaviour on growth of Atlantic cod (Gadus morhua,Linnaeus, 1758) in the North Sea

The objective of this study was to resolve key mechanisms driving individual growth patterns of Atlantic cod (Gadus morhua). Growth dynamics were analysed by linking growth patterns with stomach content composition and environmental temperature. Samples were collected in August/September of the years 2009, 2010 and 2011 in the north‐eastern part of the central North Sea. Prey selection was assessed by identification of individual prey items in the stomach content to species. Ten feeding groups were identified consisting of individuals with one prey type dominating their stomach contents (≥75% by mass), of which six were used for growth analyses: “Sandeel”, “Clupeids”, “Norway pout”, “Flatfishes”, “Crustaceans” and “Brittle stars”. For each group, growth patterns were estimated based on measures of otolith growth increments. The stomach contents showed that cod as a species are opportunistic in their prey selection, but at the same time indicated that the total, broad feeding niche width of the population is dominated by individual diet specialization and that many individuals temporally show a preference for a particular prey type. The contribution of invertebrates and particularly crustaceans decreased with increasing cod size, whereas that of fish and predominantly herring increased. Prey type had a significant effect on growth, while temperature had no effect. Slowest growth was observed in the cod group preying on sandeel, while cod preying on Norway pout showed the fastest growth. No significant difference was observed between groups preying on brittle stars, crustaceans, flatfishes and herring. Growth in the year before capture did however not differ between any of these groups. Across sampling years, growth chronology patterns were similar but not significantly influenced by temperature.     

Diel feeding habits of juveniles of Mullus surmuletus (Linneo 1758) in the lagoon of the Stagnone di Marsala (Western Sicily, Italy)

Diet composition, feeding rhythm, gastric evacuation rate and daily ration were investigated in juvenile Mullus surmuletus (Linneo 1758). Fish were collected in the lagoon of the Stagnone di Marsala in western Sicily, in July 1995, during a 24 h sampling period. Copepoda, Polychaeta, Amphipoda and Tanaidacea were shown to be the most frequent prey items. The feeding index values showed two different daily feeding times. A unimodal trend in the daily rhythm of food consumption was derived, with a peak in feeding between 1200 and 2000 h. Gastric evacuation in juvenile M. surmuletus is best described by an exponential model, with a gastric evacuation rate R  = 0.66 g h⁻¹ ( r = 0.88) ( T  = 24.45 ± 0.64°C). The amount of food consumed daily, calculated according to the Elliott and Persson model, was 0.079 g, equal to about 8% of the average dry weight of the fish.     

Diet of young-of-the-year bluefin tuna, Thunnus thynnus (Linnaeus, 1758), in the southern Tyrrhenian (Mediterranean) Sea

The diet of juvenile bluefin tuna (Thunnus thynnus) caught 2 to 8 miles off NE Sicily was investigated in order to improve knowledge of the species’ early life history. From 1998 to 2000, 107 specimens ranging from 63 to 495 mm (total length) were fished between July and November. Fishes were caught by trolling line or purse seine in a Fish Aggregating Devices (FADs) area 2 to 8 miles offshore and as by‐catch of the purse‐seine sardine fishery 2 to 4 miles offshore. Most frequently found items in the T. thynnus stomachs were fishes (84.5%), crustaceans (54.6%) and cephalopods (50.5%). The largest contribution in weight was provided by cephalopods (47.3%) and fishes (46.5%), while the most abundant items were fishes (51%), cephalopods (27.2%) and crustaceans (21.1%). These results suggest that young‐of‐the‐year tuna have an essentially piscivorous diet, although invertebrate prey provide a substantial contribution to the food array. Prey show little relationship with FADs, although one prey species (blue runner, Caranx crysos) is associated with FADs in the Mediterranean.     

Northern refugia and recent expansion in the North Sea: the case of the wrasse Symphodus melops (Linnaeus, 1758)

Pleistocene climate changes have imposed extreme conditions to intertidal rocky marine communities, forcing many species to significant range shifts in their geographical distributions. Phylogeographic analyses based on both mitochondrial and nuclear genetic markers provide a useful approach to unravel phylogeographic patterns and processes of species after this time period, to gain general knowledge of how climatic changes affect shifts in species distributions. We analyzed these patterns on the corkwing wrasse (Symphodus melops, Labridae), a rocky shore species inhabiting North Sea waters and temperate northeastern Atlantic Ocean from Norway to Morocco including the Azores, using a fragment of the mitochondrial control region and the first intron of the nuclear S7 ribosomal protein gene. We found that S. melops shows a clear differentiation between the Atlantic and the Scandinavian populations and a sharp contrast in the genetic diversity, high in the south and low in the north. Within each of these main geographic areas there is little or no genetic differentiation. The species may have persisted throughout the last glacial maximum in the southern areas as paleotemperatures were not lower than they are today in North Scandinavia. The North Sea recolonization most likely took place during the current interglacial and is dominated by a haplotype absent from the south of the study area, but present in Plymouth and Belfast. The possibility of a glacial refugium in or near the English Channel is discussed.     

Age, growth and food composition of Scorpaena porcus (Linnaeus, 1758) in the southeastern Black Sea

Samples of 525 Scorpaena porcus (Linnaeus, 1758) were collected from the southeastern Black Sea between January 2002 and May 2003 for information on age, growth, length–weight relationships and stomach contents. Total length of sampled fish ranged from 4.6 to 22.9 cm and total weight from 1.3 to 220 g. The sex ratio (1 : 1.61) was biased toward females (P < 0.05). Positive allometric growth was determined in the collected samples. The length–weight relationship for all individuals was described by the parameters a  = 0.0149 and b  = 3.09, with r ² = 0.99. The sample was composed of five age-classes (0–7 years). Three growth models were used to identify the growth characteristics: von Bertalanffy,     ; logistic,     ; and Schnute and Richards,     . Among these, the Schnute and Richards model was best fitted to the data as     The diet was composed of Carcinus mediterraneus (18.2%), Crangon crangon (12.1%), unidentified crab species (10.6%), Gobius sp. (4.6%), Palaemon sp. (4.5%), Macropipus sp. (4.5%), Engraulis encrasicholus (1.5%), Gastropoda (1.5%), and unidentified remains (34.9%).     

RFLP Analysis of Mitochondrial DNA to Evaluate Genetic Variation in Striped Red Mullet (Mullus surmuletus L.) and Red Mullet (Mullus barbatus L.) Populations

The genetic differentiation of striped red mullet (Mullus surmuletus) and red mullet (Mullus barbatus) was investigated in 6 Mediterranean populations of each species by means of restriction fragment length polymorphism analysis of mitochondrial DNA. Three segments amplified by polymerase chain reaction (control region, COI, and 12S–16S ribosomal RNA) were digested with 20 restriction endonucleases, revealing 71 haplotypes for M. surmuletus and 30 for M. barbatus. For the two species nucleotide diversity was equally distributed within and among populations, leading to N _ST values of 0.545 and 0.500 for M. surmuletus and M. barbatus, respectively. However, intrapopulation and interpopulation genetic structuring appeared to be much higher for M. surmuletus than for M. barbatus (1.88% vs. 0.46% of mean intrapopulation nucleotide diversity; 1.94% vs. 0.47% of mean interpopulation nucleotide diversity; 0.055% vs. 0.002% of net interpopulation divergence). Furthermore, 81.69% of the haplotypes observed for M. surmuletus were unique, whereas 70.29% of M. barbatus individuals were grouped in 3 common haplotypes. Given that fishing pressure and population sizes are similar for both species, this differentiation could be attributed to differences in biological parameters and life histories between the two species, coupled with oceanographic conditions prevailing in the studied area. Received July 25, 2000; accepted December 29, 2000     

Diet composition of young-of-the-year saddled bream, Oblada melanura (Linnaeus, 1758) from the eastern central Adriatic Sea

Stomach contents of 144 specimens of Oblada melanura were analyzed for diet composition. All specimens belonged to the 1‐year age group. Material was collected from the localities of Kornati Archipelago and Murter Island in the eastern central Adriatic during 1992–1993. Copepod crustaceans were the main food, while Cladocera crustaceans were the second most important. Feeding intensity was very high as indicated by high stomach fullness index and low vacuity index.     

Diet and reproductive biology of the Starred Agama,Laudakia stellio (Linnaeus, 1758) (Squamata: Agamidae), in the northern Sinai,Egypt

We quantified sexual size dimorphism, diet and reproduction in the Starred Agama, Laudakia stellio, in northern Sinai. Males were larger than females in snout-vent length and head index. The species is a sit-and-wait predator and feeds on insects, mainly coleopterans. About 30% of stomachs included plant material. No difference between sexes existed in terms of prey size preference. The reproductive season is seen to be year round with no distinctive seasonality. The smallest sexually mature female measured 92 mm SVL, whereas the smallest sexually reproductive male was 89 mm SVL. Clutch size ranged from 6 to 18 eggs.     

Age and growth of Boops boops (Linnaeus, 1758) in Izmir Bay,Aegean Sea,Turkey

The present study was conducted to determine the age relationships in lengths and weights of Boops boops (Linneaus, 1756) in Izmir Bay, central Aegean Sea. A total of 932 specimens (503 females and 429 males) were caught by gillnet, trammel net and a combination thereof on a monthly sampling basis from November 2008 through October 2009. Total length and weight of sampled fish ranged from 11.3 to 27.9 cm and from 12.2 to 261.7 g, with a mean of 19.6 cm and 82.7 g, respectively. Length‐weight relationships for all individuals were described by the parameters a = 0.0050, b = 3.237 and r² = 0.956. The von Bertalanffy growth curve fitted to the lengths‐at‐age provided parameters of L_∞ = 29.87 cm k = 0.243 and t_o = ?0.98 for males and L_∞ = 30.79 cm, k = 0.239 and t_o = ?0.90 for females. Based on otolith readings, age determinations varied from 1 to 5 years. Maximum age was 5 years in age group 2, with 29.84 and 37.97% for males and females, respectively. The overall 1 : 1.17 sex ratio of males to females was significantly biased toward females (P < 0.05). There was no statistical difference in the mean condition factor (P > 0.05), with a value of 1.028 for the entire population. The growth performance index (Φ^’) was 2.33 and 2.36 for males and females, respectively. Results were similar to other geographical areas, which suggests that a common fisheries management might be possible.