THE DISTRIBUTION AND ECOLOGY OF TWO MULLET SPECIES IN SOME FRESH WATER RIVERS IN THE EASTERN CAPE,SOUTH AFRICA

SUMMARY

Data on the relative abundance, penetration and breeding biology of the freshwater mullet Mugil cephalus and the flathead mullet Mugil cephalus in the freshwater reaches of some Eastern Cape coastal rivers are described. The differences found between the two species indicate that Myxus capensis is more specialized for a catadromous life history in an unstable riverine environment. Evidence showing the importance of the freshwater phase for the latter species is given and the disastrous effects of the erection of barriers to fish movement are stressed.     

Phylogeographic relationships among worldwide populations of the cosmopolitan marine species, the striped gray mullet (Mugil cephalus), investigated by partial cytochrome b gene sequences

Several factors such as geographical barriers, demographic history, biological and ecological traits may contribute to delineate the evolutionary history of a species. The gray mullet, Mugil cephalus, represents an interesting case of a marine species with a coastal ecology and a cosmopolitan distribution. In this study, partial cytochrome b sequences were resolved for 177 M. cephalus specimens sampled from 14 different geographic sites, in order to investigate the genetic divergence and the phylogeographic relationship among populations at a global scale. Demographic parameters were also assessed. Analysis of partial cyt b sequences showed high levels of differentiation among populations from distant geographic areas as most populations harbored private alleles and showed reciprocal monophyly. Both phylogenetic trees and haplotype network indicate the East Australian haplotypes as the closest to the ancestor sequences, which leads to the hypothesis of an Indo-West Pacific center of origin for M. cephalus. The analyses of the molecular variance showed that the genetic variation in M. cephalus is mainly harbored among populations rather than within populations. The high variability indices (h, π) calculated on M. cephalus individuals pooled together and the very low variability indices detected at some geographic sampling sites suggest that gray mullet populations have undergone a long-term reproductive isolation characterized by events of population abundance reductions which may have favored genetic differentiation among populations.     

Stability of oxidative stress biomarkers in flathead mullet,Mugil cephalus,serum during short-term storage

The production of reactive oxygen species (ROS) by aquatic organisms in response to stressful factor is a common feature in aquatic environment. Thus, the evaluation of parameters related to oxidative stress in fish, in first instance those showing the redox potential, is notable to characterize the environmental conditions.Short-term storage of samples is essential when blood must be transported from collection sites to laboratories. Therefore, excessive delays in processing might compromise the reliability of results. The aim of the present study was to assess the effect of short-term storage time at +4 °C on total oxidant status (TOS), total antioxidant capacity (TAC) and oxidative stress index (OSI) in flathead mullet (Mugil cephalus) serum. After blood collection, all sample were analyzed and the assays were repeated after 24, 48 and 72 h from sampling. results showed a significant effect of short-term storage on TOS and TAC (P ≤ 0.0001), while the statistical significance of the linear regression study for these parameters was reduced as consequence of storage. These results highlight that the activities of oxidants and antioxidants in flathead mullet serum change during short-term storage at 4 °C and should be assesses as soon as possible from collection.     

Phenetic relationships of six species of mullets (<Emphasis Type="Italic">Mugilidae</Emphasis>) from the south Adriatic,as inferred from the study of the visceral and dermal skeleton

This study examines the interspecific variability and phenetic relationships in six southern Adriatic mullet species: Mugil cephalus (Linnaeus, 1758), Chelon labrosus (Risso, 1826), Liza aurata (Risso, 1810), Liza ramada (Risso, 1826), Liza saliens (Risso, 1810), and Oedalechilus labeo (Cuvier, 1829). Twenty-three morphometric characteristics of the visceral skeleton and the dermatocranium of mullets were analyzed. The major distinguishing characters were those of the jaws. M. cephalus was clearly separated from the other species; O. labeo differed to a somewhat smaller extent; and C. labrosus was the least distinguished species. The species of the genus Liza were phenetically most similar, while the other species of mullet differed significantly from them. The greatest distances were between M. cephalus and C. labrosus, as well as between M. cephalus and O. labeo. This text was submitted by the authors in English.     

Occurrence of palytoxins in marine organisms from different trophic levels of the French Mediterranean coast harvested in 2009

Four sites located in Nice and Villefranche-sur-Mer, on the French Mediterranean coast, were monitored during the summer of 2009 for the presence of epiphytic and planktonic Ostreopsis cf. ovata, and that of palytoxin (PlTX) and 2 of its analogues (ovatoxin-a (OVTX-a) and ostreocin-D (OST-D)) in different marine organisms.Several of the 15 species that were sampled between June and September 2009 were found to be contaminated with OVTX-a as the major toxin (90% of the toxin profile) and PlTX; this included fish, echinoderms, gastropods, crustaceans and cephalopods. The contamination levels varied geographically and between species, with the herbivorous species generally having higher toxin levels than carnivorous ones.The determination of the toxin distribution between the digestive tube (DT) and the remaining tissue (RT) or roe in the case of the sea urchin Paracentrotus lividus showed that the toxins were sequestered in the DT. The highest toxin level ever recorded over the course of the study was of 392.2 μg for the sum of OVTX-a and PlTX per kg of DT of the flathead mullet Mugil cephalus. No quantifiable levels of toxins were found in the roe of the sea urchins or in the RT of the other marine products. However, in several cases, the toxin level in the whole flesh of the analysed organisms was above 30 μg OVTX-a + PlTX/kg, when knowing that the European food safety authority's opinion is that an adult should not ingest more than 30 μg PlTX + OST-D per kg of shellfish meat to avoid putting the consumer's health at risk. This was observed for the following four species: the sea urchin P. lividus, the red-mouthed rock shell Stramonita haemastoma, the warty crab Eriphia verrucosa and the flathead mullet M. cephalus.The collection of such data is of great importance to refine and complete the risk assessment of PlTX and its analogues and has to be encouraged in order to provide reliable information for setting up a regulatory level that would protect the consumers of edible marine organisms     

Cascading effects of the flathead grey mullet Mugil cephalus in freshwater eutrophic microcosmos

Flathead grey mullet (Mugil cephalus L.) stocked in fish ponds were long considered to feed primarily on detritus. However, recent research has found that they obtain much of their food from plankton and that they have a detrimental effect on pond zooplankton and large phytoplankton, whilst enhancing small phytoplankton. It has been suggested that flathead grey mullet may also increase the internal phosphorus loading of the ecosystem, which would also increase phytoplankton density. To test whether zooplankton removal or nutrient release from the sediment is the better explanation for phytoplankton enhancement in the presence of flathead grey mullet, the ecosystems of fish-less tanks, tanks with a 60 m mesh filter and tanks stocked at a fish density of 243 g m^-3 were compared. In the presence of flathead grey mullets, cladocerans, ostracods and chironomid larvae became scarcer than in the control tanks, while there were more small phytoplankton and mud snails. The green algae Cladophora sp. did not occur at all. The presence of a mechanical filter also reduced cladoceran, ostracod and chironomid densities and increased phtyoplankton and mud snail density. However, the situation observed in filter tanks was intermediate between that observed in the fish tanks and the control tanks, due to the lower filtering efficiency of the mechanical filter. The organic matter content of the sediment decreased throughout the experiment in the control and filter tanks, but remained stable in fish tanks. Phosphorus and nitrogen concentrations were not affected by any treatment. These results showed that flathead grey mullet enhanced phytoplankton development due to the removal of large cladocerans and not as a consequence of nutrient release. Furthermore, the flathead grey mullet strongly modified the benthic community, probably due to direct predation.     

The osteology of the golden grey mullet Liza aurata (Teleostei: Mugiliformes: Mugilidae) including interactive three-dimensional reconstructions

Grey mullets are remarkably characterized by their overall uniform external morphology. Identifying species as well as positioning the Mugiliformes in a phylogenetic context is rather difficult. Most recently they were placed in the newly erected Ovalentaria, but more detailed relationships to potential sister taxa were not resolved. Studying the internal morphology, especially the osteology, might provide new insights into the evolution of the Mugiliformes as well as help clarify their phylogenetic position within the Ovalentaria. A detailed osteology of the golden grey mullet Liza aurata is presented. The use of cleared and stained specimens allowed for a complete examination of bony and cartilaginous structures, and a 3D reconstruction from a μCT data set provided additional information on the positional relationships of the bones. Following this, the data obtained were compared with different mugilid species, particularly with the flathead grey mullet Mugil cephalus. Several differences between these species could be identified, such as the position of the basisphenoid, the shape of the hyomandibular and the composition of the branchial arches. These characters might help in understanding the evolutionary changes happening within the mugiliforms and will provide the basis to study this taxon in detail, finally allowing the reconstruction of the body plan of grey mullets.     

Identification of the sex‐determining region in flathead grey mullet (Mugil cephalus)

Elucidation of the sex‐determination mechanism in flathead grey mullet (Mugil cephalus) is required to exploit its economic potential by production of genetically determined monosex populations and application of hormonal treatment to parents rather than to the marketed progeny. Our objective was to construct a first‐generation linkage map of the M. cephalus in order to identify the sex‐determining region and sex‐determination system. Deep‐sequencing data of a single male was assembled and aligned to the genome of Nile tilapia (Oreochromis niloticus). A total 245 M. cephalus microsatellite markers were designed, spanning the syntenic tilapia genome assembly at intervals of 10 Mb. In the mapping family of full‐sib progeny, 156 segregating markers were used to construct a first‐generation linkage map of 24 linkage groups (LGs), corresponding to the number of chromosomes. The linkage map spanned approximately 1200 cM with an average inter‐marker distance of 10.6 cM. Markers segregating on LG9 in two independent mapping families showed nearly complete concordance with gender (R² = 0.95). The sex determining locus was fine mapped within an interval of 8.6 cM on LG9. The sex of offspring was determined only by the alleles transmitted from the father, thus indicating an XY sex‐determination system.     

Population genetic structure of striped mullet, Mugil cephalus, along the coast of China, inferred by AFLP fingerprinting

The striped mullet, Mugil cephalus, is an economically important species for both aquaculture and commercial fisheries in China. In this study, the amplified fragment length polymorphism (AFLP) technique was employed to analyze population genetic diversity and genetic distance between different populations with the aim of elucidating the population structure and gene flow of M. cephalus along the coast of China. A total of 230 fragments with 150–500 bp were identified from 118 individuals by five AFLP primer combinations. The polymorphic loci within populations varied from 46.52% to 64.78%, with an average of 53.91%, and the average heterozygosity from 0.1829 to 0.2282, with an average of 0.2074. The UPGMA phenograms of 118 individuals were constructed based on Dice similarity coefficients and four clusters were recognized. AMOVA analysis revealed that 60.7% of genetic variations were within populations and 39.3% between populations. The estimated genetic distance (φ_ST) value over all polymorphic loci across the six populations was 0.393 (p < 0.0010), indicating a strong population structuring. The pairwise φ_ST value ranged from 0.1112 to 0.5358, with an average of 0.3693. The population pairwise gene flows (average N_m = 0.73) are low. In addition, the result of the Mantel test showed that there was a significant correlation between geographic and genetic distances (r = 0.5434, p = 0.0050). It was speculated that there exist at least four distinct geographic populational subdivisions of M. cephalus along the Chinese coast. This research has provided new molecular data which will aid our understanding of the genetic structure of this species.     

Sex‐specific daily spawning seaward migration of striped mullet Mugil cephalus in a coastal lagoon

The sex‐specific daily spawning seaward migration of striped mullet Mugil cephalus was analysed in Palaiopotamos Lagoon (western Greek coast, eastern Mediterranean Sea) in an 86 day time series. The data set included the daily number of M. cephalus catches in barrier traps, as well as a time series of some weather variables. The analysis revealed an important linkage of the daily migration rate as well as a sex‐specific response of the species to the lunar cycle and the short‐term fluctuation of weather variables. The daily migration pattern of females was more persistent than that of males, indicating a possible female leadership role during the spawning migration. Multiregression models described quite accurately the sex‐specific daily migration rates of the species, thus providing a potentially powerful tool regarding the lagoon fishery management of M. cephalus, especially in the context of climate change.     

Fishery, seasonal abundance and mortality of grey mullets (Pisces: Mugilidae) in Negombo Lagoon, Sri Lanka

The seasonal abundance and instantaneous natural and fishing mortalities of six species of grey mullets, namely Liza subviridis, L. macrolepis, L. tade, Mugil cephalus, Valamugil buchanani and V. cunnesius were studied as a prelude for the management of their fishery in Negombo lagoon (7°10′N and 79°50′E). L. subviridis was the most abundant of the grey mullet species in the commercial catches and accounted for 37% of the total grey mullet catch. M. cephalus was the least abundant and constituted 6%. The annual catch of grey mullets was estimated to be around 23 000 kg (5.67 kg/ha); about 40 % of the total fish landings of the lagoon. The seasonal variation in the catch of different species of grey mullets appear to be related to their breeding seasons and spawning migrations. The highest value for instantaneous natural and fishing mortalities, which were 1.04 and 0.94 respectively were obtained for V. cunnesius. The lowest values for instantaneous natural and fishing mortalities which were 0.51 and 0.19 respectively were obtained for M. cephalus. The exploitation ratios calculated were less than 0.5 for all species other than L. tade which suggest that the grey mullet populations excluding L. tade in this lagoon may presently be underexploited.     

Inter- and intraspecific partitioning of food resources by six large and abundant fish species in a seasonally open estuary

This study has tested the hypotheses that the dietary compositions of the six large and abundant fish species in the 46 km² basin of a seasonally open estuary (Wilson Inlet) will differ significantly, change with increasing body size and vary with water depth and season. These species comprise four marine species, the sea mullet Mugil cephalus, yellow‐eye mullet Aldrichetta forsteri, King George whiting Sillaginodes punctata and Australian herring Arripis georgiana, and populations of two species that are confined to the estuary, the cobbler Cnidoglanis macrocephalus and the southern blue‐spotted flathead Platycephalus speculator. Non‐metric multidimensional ordination and associated tests showed that, overall, the dietary composition was influenced to a far greater extent by the species of fish than by either water depth or season. At even a relatively broad level of taxonomic discrimination, the dietary compositions of each pair of species were significantly different, except for those of A. georgiana v. P. speculator, and even in that case those of their larger individuals differed. Differences among the diets of the six species, which represented five families, are related to differences in feeding morphology and location within the water column. Mugil cephalus ingested almost exclusively sediment and fine organic material. Although A. forsteri and S. punctata both consumed substantial amounts of polychaetes (including nereids, capitellids and orbiniids), the former ingested relatively larger volumes of small crustaceans (copepods) and relatively lower volumes of large crustaceans (the carid Palaemonetes australis), nemertines and bivalve siphons. The diets of A. georgiana and P. speculator were both typified by the consistent and high contributions of large crustaceans and fishes. Among fish prey, however, A. georgiana focused to a far greater extent on the small clupeid Engraulis australis, whereas P. speculator consumed a wider range of teleosts, which included species of atherinid and goby. Although the diets of A. forsteri and C. macrocephalus both contained substantial amounts of coarse organic material, the latter differed markedly from those of all other species by the frequent presence of mytilids (mainly Xenostrobus spp.) and other bivalves (especially Tellina deltoidalis and Irus crenata). The diets of each species except M. cephalus changed with increasing body size and, for comparable size classes, did not differ between shallow and deeper waters. The partitioning of food resources within and among the six large and abundant fish species found in Wilson Inlet would reduce the potential for competition for these resources and help account for the large numbers of those species in this seasonally open estuary.     

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.     

Aldrin Epoxidation in Flathead Mullet (Mugil cephalus): Possible Involvement of CYP1A and CYP3A

The primary objective of this study was to determine specific cytochrome P450 isozyme(s) involved in the metabolism of aldrin to its toxic metabolite dieldrin in flathead mullet (Mugil cephalus) liver microsomes. To identify the cytochrome P450 isozyme responsible for the aldrin metabolism in mullet liver, the effects of mammalian‐specific cytochrome P450 inhibitors and substrates were determined in the epoxidation reaction of aldrin. CYP3A‐related inhibitors, ketoconazole, SKF‐525A, and cimetidine, inhibited the metabolism of aldrin. The contribution of CYP1A to the aldrin metabolism was shown by the inhibition of 7‐ethoxyresorufin‐O‐deethylase activity in the presence of aldrin. The results indicate that CY1A and CYP3A are the cytochrome P450s involved in aldrin epoxidase activity in mullet. In addition, the suitability of aldrin epoxidase activity for monitoring of environmental pollution was also assessed in the fish samples caught from four different locations of the West Black Sea coast of Turkey.     

Morphologic and Genetic Evidence for Mixed Infection with Two Myxobolus Species (Myxozoa: Myxobolidae) in Gray Mullets,Mugil cephalus,from Korean Waters

The present study was performed to trace the decisive evidence for mixed infection of 2 Myxobolus species, M. episquamalis and Myxobolus sp., in the gray mullet, Mugil cephalus, from Korean waters. Mullets with whitish cyst-like plasmodia on their scales were collected near a sewage plant in Yeosu, southern part of Korea, in 2009. The cysts were mainly located on scales and also found in the intestine. The spores from scales were oval in a frontal view, tapering anteriorly to a blunt apex, and measured 7.2 µm (5.8-8.0) in length and 5.3 µm (4.7-6.1) in width. Two polar capsules were pyriform and extended over the anterior half of the spore, measuring 3.5 µm (2.3-4.8) in length and 2.0 µm (1.5-2.2) in width. In contrast, the spores from the intestine were ellipsoidal, 10.4 µm (9.0-11.9) in length and 8.4 µm (7.3-10.1) in width. The polar capsules were pyriform but did not extend over the anterior half of the spore, 3.7 µm (2.5-4.5) in length and 2.2 µm (1.8-2.9) in width. The nucleotide sequences of the 18S rDNA gene of the 2 myxosporean spores from scales and intestine showed 88.1% identity to each other and 100% identity with M. episquamalis and 94.5% identity with M. spinacurvatura from mullet, respectively. By the above findings, it is first confirmed that mullets from the Korean water are infected with 2 myxosporean species, M. episquamalis and Myxobolus sp.     

Ultrastructural study of the esophagus of seawater-and freshwater-acclimated Mugil cephalus (Perciformes,Mugilidae), euryhaline marine fish

The esophagus of the common grey mullet Mugil cephalus shows a single mode of organization that is common to both seawater- and freshwater-acclimated specimens. A short anterior segment is lined by a stratified epithelium with mucous cells; posteriorly, this is progressively replaced by single-layered columnar epithelium. Ultrastructural features of the columnar epithelium are quite similar in the seawater- and freshwater-acclimated specimens. Apical microvillous projections, lamellar structures, and dilated intercellular spaces are observed. The present study suggests that the mullet esophagus is involved in active ion transport and water permeability, both in seawater and in freshwater environments. © 1993 Wiley-Liss, Inc.     

How an invasive alga species (<Emphasis Type="Italic">Caulerpa taxifolia</Emphasis>) induces changes in foraging strategies of the benthivorous fish <Emphasis Type="Italic">Mullus surmuletus</Emphasis> in coastal Mediterranean ecosystems

The foraging behaviour variability of three striped red mullet (Mullus surmuletus L. 1758) populations with respect to the vegetation cover was examined along the French Mediterranean coasts. We tested both the carrying capacity of different habitats and the hypothesis of a food segregation by the invasive alga Caulerpa taxifolia (Vahl) C. Agardh, on the functioning of benthic fish populations. The results indicated a significant site effect on M. surmuletus foraging behaviour and movements. The vegetation cover may play an important role in modifying the striped red mullet cost of foraging (sampling effort) and thus its strategy of prey capture. As long as the cover of marine phanerogams and/or macrophyte algae (Caulerpaceae) increases, the foraging budget and the distances covered in search of prey decrease significantly. Similarly, the striped red mullet increases the prospected sample periods to augment its foraging success, swimming above the bottom. These changes are related to the development of a dense superficial network of plagiotropic rhizomes and stolons, and to the reduction of space between fronds that limits the accessibility to resources and may increase intra-specific food competition. The role of C. taxifolia does not differ from that of other marine phanerogams but induces significant changes in the structure of Mullidae populations at the local level. The rapid expansion of Caulerpaceae in the Mediterranean Sea could constitute a real threat for the balance of the marine coastal biodiversity and the ecology of M. surmuletus, which is considered a flagship species for coastal Mediterranean demersal fisheries.     

Mitochondrial DNA divergence and phylogenetic relationships in mullets (Pisces: Mugilidae) of the Sea of Japan and the Sea of Azov revealed by PCR-RFLP-analysis

Three Mugilid species: Mugil cephalus (Linnaeus, 1758) and Liza haematocheila (Temminck et Schlegel, 1845; syn. Mugil soiuy, M. haematocheilus, L. soiuy, Chelon haematocheilus) from the Sea of Japan, as well as M. cephalus and Liza aurata (Risso, 1810) from the Sea of Azov were investigated on the basis of PCR-RFLP analysis of mitochondrial DNA (mtDNA) fragments, which included 12S/16S rRNA, and ND3/ND4L/ND4 genes. Among 61 individuals of three Mugilid species thirteen different haplotypes were detected. Eight and thirteen restriction endonucleases were found to be species-specific in 12S/16SrRNA and ND3/ND4L/ND4 respectively. This method may be useful for species identification. M. cephalus showed the largest genetic divergence while L. haematocheila and L. aurata were closely related and clustered together. The level of mtDNA differentiation between the two M. cephalus samples from the Sea of Japan and the Sea of Azov, i.e., nucleotide substitutions of approximately 3%, appeared to be relatively high.     

A review of changes in the fish assemblages of Levantine inland and marine ecosystems following the introduction of non-native fishes

The arrival of non‐native fishes in the Levant Basin began in the late 19th century. Whereas the presence of most of the 40 non‐native freshwater fishes stem from intentional introductions, either for aquaculture or pest control, the 62 species of non‐native marine fishes arrived by natural dispersal via the Suez Canal. Of the non‐native freshwater species, five have established successful breeding populations (mosquitofish Gambusia affinis, common carp Cyprinus carpio, crucian carp Carassius carassius, swordtail Xiphophorus hellerii and rainbow trout Oncorhynchus mykiss), and seven are regularly stocked in natural habitats (thinlip mullet Liza ramada, flathead mullet Mugil cephalus, European eel Anguilla anguilla, grass carp Ctenopharyngodon idella, Asian silver carp Hypophthalmichthys molitrix, bighead carp Aristichthys nobilis, black carp Mylopharyngodon piceus). Some non‐native species appear to have out‐competed native species. Gambusia affinis may have caused the extirpation of two native cyprinid fishes from the Qishon River basin (Levant silver carp Hemigrammocapoeta nana and common garra Garra rufa) and the southern Dead Sea (endemic Sodom's garra G. ghoerensis). The opening of the Suez Canal in 1869 allowed entry into the eastern Mediterranean of Indo‐Pacific and Erythrean biota, with the latter now dominating the community structure (50–90% of fish biomass) and function (altered native food web) of the Levantine littoral and infra‐littoral zones. The process has accelerated in recent years concurrent with a warming trend of the seawater. Record numbers of newly discovered non‐native species is leading to the creation of a human‐assisted Erythrean biotic province in the eastern Mediterranean.