Osmoregulation and differential penetration of two grey mullets, Chelon labrosus (Risso) and Liza ramada (Risso) in estuarine fish ponds

Grey mullet ponds situated in Arcachon Bay on the western Atlantic coast of France, display contrasting mixohaline habitats.The pattern of osmoregulation of Chelon labrosus and Liza ramada exhibiting differential penetration of fish ponds has been investigated. Key variables of salinity and temperature have been considered. The tolerances to low salinities and to fresh water have been determined. The dynamics of variation in plasma osmotic pressure and major plasma electrolytes (Na⁺, Cl^?, K⁺) were studied in terms of: (1) gradual adaptation to a decreasing salinity gradient; (2) effects of a long-term adaptation in fresh water; (3) effects of low temperatures on sea water adapted fish.Both species can adapt to a wide range of salinities; however, while L. ramada show a good hypoosmotic regulation, with no alteration in plasma concentration over a wide range of salinity and after a long stay (5 months) in fresh water, C. labrosus cannot live for long periods of time in a wholly fresh water habitat. Both field samples obtained from thick-lipped grey mullets forced to stay in a freshwater pond and experimentally adapted fish showed, after 3 months, an unequivoqual decrease in plasma sodium and chloride, and plasma osmolality decreased to the same extent; this pattern of no compensation is bound, sooner or later, to end in death. The inability of C. labrosus to develop a long-term hypoosmoregulation in fresh water is referred to salinity preferences which probably limit the upstream penetration of this species.Plasma osmolality and major electrolytes (sodium and chloride) increased in cold (4 °C) sea water. This response might be due to a reduced ability of grey mullets to osmoregulate in cold waters. In the poly-mesohaline ponds, Winter drop in temperature (4–6 °C) causes grey mullets to migrate to the meso-oligohaline ponds where the mean temperature is more elevated (8 °C) and temperature changes less rapid (6–9 °C).     

One century of eel growth: changes and implications

Abstract – A cooperative effort gathered a large European length‐at‐age data set (N = 45,759, Lat. 36S–61N Long. 10W–27E) for Anguilla anguilla, covering one century. To assess the effect of global warming during the last century and habitat effects on growth, a model was fitted on the data representing the conditions met at the distribution area scale. Two GLMs were designed to predict eel log(GR): one model was fitted to the whole data and the other was fitted to the female data subset. A model selection procedure was applied to select the best predictors among sex, age class, five temperature parameters and six habitat parameters (depth, salinity and four variables related to the position in the catchment). The yearly sum of temperatures above 13 °C (TempSUP13), the relative distance within the catchment, sex, age class, salinity class and depth class were finally selected. The best model predicted eel log(GR) with a 64.46% accuracy for the whole data and 66.91% for the female eel data. Growth rate (GR) was greater in habitats close to the sea and in deep habitats. TempSUP13 variable had one of the greatest predictive powers in the model, showing that global warming had affected eel growth during the last century.     

The identification of grey mullet species by disc electrophoresis

Electrophoresis was carried out on the water-soluble muscle protein (myogen) of six grey mullets (Mugilidae), caught off the Mediterranean coast of Israel. With the obtained electropherograms it was possible to identify the adults and juveniles of five species of grey mullet. A tentative key for species determination based on the myogen electrophoretic pattern of five species (Liza ramada (Risso, 1826), L. aurata (Risso, 1810), L. provensalis (Risso, 1826), L. saliens (Risso, 1810) and Mugil cephalus (Linnaeus, 1758)) is given. Of the sixth species, Oedalechilus labeo (Cuvier, 1829), only one small adult and six juvenile specimens were obtained.A fast moving band occurred in the pattern of all juveniles of the investigated species. This fraction decreased during growth of all species, it became faint in adults of L. saliens, L. provensalis and L. ramada and was not observed in adult L. aurata and M. cephalus.     

Histopathological and ultrastructural assessment of two mugilid species infected with myxozoans and helminths

The histopathology and ultrastructure of the intestine of mullets, Liza ramada and Liza saliens, from Comacchio lagoons (northern Italy) naturally infected with myxozoans and helminths were investigated and described. Sixty‐two (80.5%) of 77 mullets harboured one or more of the following parasites species: Myxobolus mugchelo (Myxozoa), Neoechinorhynchus agilis (Acanthocephala), Haplosplanchnus pachysomus and Dicrogaster contractus (Digenea). Co‐occurrence of helminths with myxozoans was common. The main damage caused by digeneans was destruction of the mucosal epithelium of the villi, necrosis and degeneration of intestinal epithelial cells. More severe intestinal damage was caused by acanthocephalans which reach the submucosa layer with their proboscis. At the site of helminths infection, several mast cells (MCs), rodlet cells (RCs), mucous cells and few neutrophils and macrophages were observed in the epithelium. RCs and mucous cells exhibited discharge activity in close vicinity to the worm's tegument. M. mugchelo conspicuous plasmodia were encysted mainly in muscle and submucosa layers of the intestine. Indeed, spores of M. mugchelo were documented within the epithelial cells of host intestine and in proximity to MCs. Degranulation of the MCs near the myxozoans was very frequent.     

Infection by Anguillicoloides crassus in a riverine stock of European eel,Anguilla anguilla

Abstract Infection by the parasitic nematode Anguillicoloides crassus Kuwahara, Niimi & Itagaki, in a wild riverine stock of European eel, Anguilla anguilla (L.), in a near pristine river was investigated. Samples were collected on a seasonal basis in distinct habitats along the river gradient. This study highlighted the presence of the parasite and completion of the whole life cycle in eels from the Río Esva. Infection levels by A. crassus were high at three sites between the mid river to the estuary and also varied among seasons. Condition of eels was lower at upstream sites compared with downstream locations. Although high‐quality, environmental conditions in the Río Esva may buffer the effects of A. crassus on eels, potential impacts and limiting factors for the parasite are discussed.     

Rapid response of fish and aquatic habitat to removal of a tidal barrier

1. River barrier removal is used increasingly as a conservation tool to restore lotic habitat and river connectivity, but evidence of its efficacy is incomplete. This study used a before–after methodology to determine the effects of removing a tidal-limit barrier on the fishes, macroinvertebrates, and habitats of an English coastal stream.
2. Following barrier removal, habitat diversity increased immediately upstream and remained similar downstream. Mobilized silt altered the substrate composition immediately downstream, but this was temporary as silt was flushed out the following winter. Changes to macroinvertebrate communities occurred upstream and downstream of the former barrier but these were transient.
3. A dramatic and sustained increase in fish density occurred immediately upstream of the barrier after its removal, but effects downstream were minor. The fish community upstream changed, largely due to rapid recruitment and dispersal of endangered European eel (Anguilla anguilla). Eel density in the formerly impounded zone increased from 0.5 per 100 m² before barrier removal to 32.5 per 100 m² 5 months after removal. By 17 months after barrier removal there was no difference in eel density across the six sections sampled.
4. Although resident stream fishes such as bullhead (Cottus gobio species complex, protected under the European Habitats Directive) were abundant in middle and upper-stream sections, brown trout (Salmo trutta, a listed species for biodiversity conservation in England and Wales) density remained low during the study and recruitment was poor. This suggests that although colonization access for anadromous trout was available, habitat upstream may have been unsuitable for reproduction, indicating that wider catchment management is required to complement the restoration of connectivity.
5. These findings suggest that tidal barrier removal is an effective method of restoring lotic habitats and connectivity, and can be beneficial for resident and migratory fishes including those of conservation importance (e.g. European eel) in coastal streams.

     

Chemical composition of alimentary canal contents of mullet (Teleostei: Mugilidae) caught in the Swartkops Estuary near Port Elizabeth,South Africa

Composition of alimentary canal contents (protein, ash, moisture and carbohydrate by difference) of four mullet species from the Swartkops Estuary, were determined monthly over a 13-month period. It was found that Liza tricuspidens consumed the most nutritious (highest protein and carbohydrate and lowest ash) material followed by Mugil cephalus, Liza richardsoni and lastly Liza dumerili, the most abundant mullet species in the estuary. It was also found that smaller specimens, irrespective of species, consumed the most nutritious food material. An attempt was made to relate chemical composition to the particular food and substrate preference of each species. Correlation coefficients between moisture and protein (positive), moisture and ash (negative) and ash and protein (negative) enabled the calculation of regression equations by which protein and ash can be determined from a relatively simple moisture determination.     

Occurrence of estuarine and sea eels <Emphasis Type="Italic">Anguilla japonica</Emphasis> and a migrating silver eel <Emphasis Type="Italic">Anguilla anguilla</Emphasis> in the Tokyo Bay area,Japan

Otolith microchemical analyses of the strontium (Sr) and calcium (Ca) concentrations in the eels Anguilla japonica and A. anguilla caught in Tokyo Bay were undertaken to reconstruct the eels’ migratory histories. A. japonica in the yellow stage (immature stage) were caught in a bay without any adjacent rivers or streams. A. anguilla was in the silver stage (early maturing stage), and the eel was confirmed to have just begun spawning migration to the open ocean from Tokyo Bay based on the otolith Sr:Ca ratios, which showed a typical catadromous life history with low Sr:Ca ratio values throughout the eel’s life after recruitment. The mean Sr:Ca ratios in A. japonica from the elver mark to the otolith edge indicated the eels belonged to several general categories of migratory histories, including sea eels (average Sr:Ca ratio ≥6.0 × 10⁻³) and estuarine eels (average Sr:Ca ratio 2.5 to 6.0 × 10⁻³) based on the criteria reported previously in A. japonica. All eels had a certain freshwater life period, although the period was highly variable among fish. These results indicate that A. japonica has a flexible pattern of migration, with the ability to adapt to various habitats and salinities.     

Newcomers in the Baltic Sea: an attempt to trace the origins and whereabouts of thicklip grey mullet <Emphasis Type="Italic">Chelon labrosus</Emphasis>

In recent years, thicklip grey mullet Chelon labrosus has shown increasing expansion of its native habitats in the north-eastern Atlantic into northerly adjacent areas including the North Sea and the brackish Baltic Sea. Despite the regular annual and seasonal occurrence of C. labrosus in the western Baltic during the warm months, nothing is known of the origin or whereabouts of the mullet during the cold season. As different possible migration scenarios can be considered, we performed otolith microchemistry analyses on specimens from the western Baltic Sea to identify the origin of this nonindigenous species. Comparison with North Sea samples revealed common habitat preferences and underlined the highly euryhaline nature of C. labrosus in different recently occupied habitats. Occasional fluctuations of Sr/Ca ratio along the growth axis suggest periodical migration between waters of different salinities but did not reveal distinct migration pathways.     

Genetic identification and phylogenetic inferences in different Mugilidae species using 5S rDNA markers

A DNA methodology was developed to discriminate fry of six Mugilidae species found in the Mediterranean, namely Mugil cephalus, Mugil so‐iuy, Chelon labrosus, Liza aurata, Liza ramada and Liza saliens. Polymerase chain reaction (PCR) amplification of the 5S rDNA gene was used for the identification of the above six species. PCR products of two species showed different patterns on EtBr‐stained agarose gels; M. so‐iuy gave a pattern of three bands, while L. saliens gave a pattern of one band. Mugil cephalus, C. labrosus, L. aurata and L. ramada gave a pattern of two bands. Subsequent sequencing analyses revealed unique haplotypes for each of the remaining four species. This is a genetic technique that could be applied in hatcheries, for identification of fry mullet's species. Furthermore, 5S rDNA sequences of each of five of the studied species (i.e. M. cephalus, C. labrosus, L. aurata, L. ramada and L. saliens), as well as a sequence of Oedalechilus labeo that belongs to the Mugilidae family, were aligned and used for the examination of the phylogenetic relationships among them. Phylogenetic trees produced in our study are in general agreement with those presented in the literature. This is the first study to use a nuclear marker to elucidate the phylogeny of Mugilidae species.     

Long‐term records (1781–2013) of European eel (Anguilla anguilla L.) production in the Comacchio Lagoon (Italy): evaluation of local and global factors as causes of the population collapse

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Environmental influences on the recruitment dynamics of juvenile European eels,Anguilla anguilla,in a small estuary of the Tyrrhenian Sea,Sardinia, Italy

1. The European eel, Anguilla anguilla, is a catadromous and migratory species of commercial importance. Its complex life cycle results in its exposure to many risk factors, which have resulted in stock declines across all life stages since the 1970s.
2. The temporal recruitment dynamics of juvenile eels (glass eels and elvers) were investigated in a small Mediterranean estuary (Sardinia, Italy). The composition of the population and the monthly and seasonal variations in the abundances of juvenile eels was assessed over 78 sampling events (from February 2017 to February 2018). Furthermore, the effects of abiotic variables on the abundances of glass eels and elvers were investigated using generalized additive models (GAMs).
3. Glass eels had the greatest abundance during the winter months, whereas elvers had the greatest abundance during spring. Modelling revealed that the abundance of glass eels was mostly explained by the combined effects of water temperature (12.3–14.5 °C), tidal coefficient (40–110 cm), moon phase, season, and river mouth condition, whereas the abundance of elvers was associated with water temperature (14–21 °C), dissolved oxygen content (>7 mg/L), and season. These results suggest that the annual recruitment of juvenile eels occurs throughout the year, with clear seasonal migration dynamics.
4. The use of multiple statistical approaches allowed us to identify the importance of several environmental variables in regulating the recruitment dynamics, providing useful information for conserving eel stocks through the restoration of the natural flow regime and the connectivity between freshwater habitats and the sea.

     

On the grey mullets of the Nigerian coast,prospects of their culture and results of trials

Mullets have so far been recorded in the brackish water areas only and of the 8 species identified, Liza falcipinnis is the most abundant. Mullet fry (mixed species) are available throughout the year but in greater quantities between March and July. It is estimated that enough fry to stock more than 10 000 ha for polyculture can be collected from the coastal areas. With a view to culturing them in fresh water, it has been possible to acclimatize them to fresh water. This offers good prospects of culturing mullets together with common carp, catfish (Chrysichthys nigrodigitatus) and cichlias (Tilapia sp.)Polyculture trials in brackishwater ponds in Lagos indicate that the natural entry of mullet fry with the tide could result in productions of up to 239 kg ha^?1 year^?1 in addition to that of other species, without supplementary feed or fertilizer. Stocking of mullet fry increased the mullet yield. Experiments indicate that supplementary feed also increases both yield and average size. Predators such as Sphyraena sp. reduce mullet population in fish ponds and also their yield.     

Integrating in situ quantitative geographic information tools and size‐specific,laboratory‐based growth zones in a dynamic river‐mouth estuary

• 1. The ultimate determination of coastal habitat suitability requires the integration of both dynamic (i.e. water mass characteristics) and stationary (structural) habitats. An approach using real‐time streamed data collection, remote sensing, and GIS modelling to compare and contrast seasonal and spatial patterns in these habitat components of the eastern and western distributaries of the lower Pascagoula River estuary is described.
• 2. Structural and dynamic habitat characteristics are described using GIS and integrated with published growth data on juvenile mullet (Mugil spp.) and spot (Leiostomus xanthurus) to reveal zones of accelerated growth. Both mullet and spot had their greatest growth when water temperature and salinity (dynamic habitat) were physiologically optimal. The lack of spatial difference in the dynamic habitat between distributaries resulted in no growth zone differences for both species.
• 3. The integration of the growth zones with the structural habitat component showed that the west distributary, with its greater availability and reduced fragmentation of main channel marsh edge, should provide a greater area of essential fish habitat than the east distributary for juvenile spot, a marsh‐edge associate. Because juvenile mullet are less associated with structural wetland habitat, growth zones and the stationary (structural) habitat were not integrated.
• 4. The approach of integrating real‐time geo‐referenced water quality data with regional fish growth‐rate data is an important step towards a quantitative understanding of the hierarchical nature and inherent variability of dynamic coastal environments. The use of this holistic approach should lead to more effective management of estuarine systems, especially in regard to potential impacts within the estuary's watershed and to its coupling with offshore environments.

Copyright © 2007 John Wiley & Sons, Ltd.     

Phylogenetic relationships in grey mullets (Mugilidae) in a Tunisian lagoon

The Mugilidae family is an important fish group representing a major source for fisheries and aquaculture. In the south Mediterranean bank, no data are available on this fauna, except for some morphological studies on Tunisian samples. In this study, 16 allozymic loci were used to investigate the phylogenetic relationships within Tunisian mugilids. The results obtained from Hergla lagoon samples highlight five operational taxonomic unit corresponding to the well‐known species (Liza aurata, Liza ramada, Liza saliens, Chelon labrosus, Mugil cephalus). Several loci appeared to be diagnostic of these species, but in contrast to Greek mugilid samples, we did not find any diagnostic locus fixed differently for the five species. These results can help aquaculture units to identify accurately the mullet species they subsequently use for stocking aquaculture ponds and inland waters. However, species identity represents very important information, as each species has a different growth rate and salinity tolerance. On the other hand, when compared with North Mediterranean Mugilidae analysed until now, Tunisian samples show a genetic differentiation that could be related to different physicochemical conditions between the North and South banks, similar to those recorded in the eastern and western two Mediterranean basins separated by the Siculo‐Tunisian strait. In addition, this study confirms the morphological taxonomy, except for the subdivision of the Liza genus into two sub‐genera. The phylogenetic tree is in agreement with that on Languedoc Mugilidae samples (France), indicating that the subdivision of the Liza genus into two sub‐genera appears to be without any genetic base.     

PARASITES AND PARASITOSIS IN FISH CULTURE IN PORTUGAL

This paper deals with research work covering the period from May 1979 up to May 1981 and presents results of parasites and parasitosis diagnosed in a total of 195 complete dissections of six fish species from cultured and feral populations in Portugal: European eel (Anguilla anguilla) (49); mirror carp (Cyprinus carpio specularis) (29); common grey mullet (Mugil cephalus) (18); European plaice (Pleuronectes platessa) (11); rainbow trout (Salmo gairdneri) (42); common sole (Solea solea) (46). A list of protozoans and helminths identified with respective incidence is given: A) Feral fish: 1) European eel (17)—Echinorhynchus clavula 11.8% and Rhabdochona anguilla 5.9%; 2) common grey mullet (18)—Haploporus benedenii 16.7%, Neoechinorhynchus sp. 5.6%, and Raphidascaris sp. 5.6%; 3) European plaice (11)—Bothriocephalus sp. larvae 9.1%, Contracaecum aduncum 9.1%, and Cryptocotyle lingua 9.1%; 4) common sole (46)—Cucullanellus minutus 8.7%, Gyrodactylus elegans 4.3%, and Cestodes larvae 2.2%. B) Cultured fish: 1) European eel (32)—Trichodina anguillae 3.1% and Ichthyophthirius multifiliis 18.8%; 2) rainbow trout (42)—Eimeria truttae 2.4%, Hexamita intestinalis 4.8%, Holophrya simplex 2.4%, and Trichodina truttae 4.8%. The results show that feral fish harbor predominantly indirect life cycle helminths, in contrast with cultured fish only affected with protozoans, due mainly to overcrowding and deficient management, which propitiate a significant background infection. It was in these specimens that some lesions characteristic of protozoosis were found.     

Changes in the diet of a recovering Eurasian otter population between the 1970s and 2010

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Unravelling the complex habitat use of the white mullet,Mugil curema,in several coastal environments from Neotropical Pacific and Atlantic waters

1. The white mullet, Mugil curema, is a widely distributed euryhaline species, the migratory behaviour of which is poorly understood. The objective of this work was to study the large-scale habitat use of this species for the first time. Several environments were considered, such as euryhaline and hypersaline lagoons, the sea, and a river, distributed in the Central Pacific (Mexico) and Atlantic (Gulf of Mexico, Caribbean Sea-Venezuela, and north-eastern Brazil).
2. Otolith core-to-edge Sr/Ca ratios of 163 fish, determined by laser ablation inductively coupled plasma mass spectrometry, were used to study the salinity-habitat migration history of the fish. Fish from Mexico (Tamiahua Lagoon, n = 4; Alvarado Lagoon, n = 2), Venezuela (n = 1), and Brazil (n = 12) (11.1% of the total) showed high Sr/Ca values at early life stages and were classified as marine estuarine opportunists. Two specimens (from Alvarado Lagoon and Balsas River, Mexico) showed Sr/Ca values consistently below the high salinity guide value (salinity < 33.5). For the rest of the fish (87.1%), the Sr/Ca ratio suggested a displacement from the estuary towards the sea or hypersaline environments, and so these fish were classified as estuarine migrants.
3. A change-point analysis identified six individuals with a single stable otolith Sr/Ca signature through ontogeny (three from Brazil, one from Venezuela, and two from Tamiahua Lagoon, Mexico), suggesting limited displacement between environments with different salinities. The rest of the individuals showed between two and 10 changes in stable Sr/Ca signatures (mean = 4.07 ± 1.85). The highest number of changes in Sr/Ca ratio (4.87 ± 1.1) was found in fish from Laguna Madre (Mexico) and the lowest was found in fish from Brazil (3.27 ± 1.70) (H = 19.8, p = 0.002).
4. Otolith Sr/Ca time series suggest that the migratory estuarine pattern is the most common throughout the study area. This work highlights that the sustainable use of M. curema depends on the conservation of estuaries and the corridors between them and other environments such as lagoons, rivers, mangroves and the sea.

     

Ecology and conservation of the American eel in the Caribbean region

The majority of American eel, Anguilla rostrata LeSueur, knowledge is derived from temperate regions in the United States and Canada, with little known from its tropical Caribbean distribution. Findings of original research on American eel distribution, abundance, population biology, habitat ecology and threats from the Caribbean island of Puerto Rico were synthesised. American eel were captured from 48 of 116 sites (41.4%) in 26 of 49 river basins (53.1%) during 2005–2016, and it was extirpated upstream of dams and migration barriers >3.0 m high (38.9% of habitat). Mean density and biomass were 438.9 fish/ha and 23.44 kg/ha, respectively. Upstream habitats favoured larger individuals, and females were larger than males. The swim‐bladder parasite Anguillicoloides crassus Kuwahara, Niimi & Hagaki was not found in 120 eels examined. Realised threats include dams and other migratory barriers, habitat loss and alteration and pollution; exotic species and commercial fishing are impending threats; and the least understood is climate change.