Studies on scale structure in the common goby Pomatoschistus microps Krøyer

A histological study on scale structure in the common goby, Pomatoschistus microps (Krøyer) has established a similarity to other teleost scales, but yielded two new findings. First, the osseous layer of the scale was formed of successive and parallel calcified bands that may reflect a rhythm in scale growth. Second, extracellular matrix vesicles (100–200 nm) were identified by electron microscopy, at the calcifying area in the anterior growing edge of the scale; distribution of these vesicles corresponded closely to the pattern of scale calcification. A proposal on the mechanism of growth and calcification of scale has been made. The surface topography of the scale has also been examined by scanning electron microscopy. The raised edge of the circulus is formed of minute knobs, which may be used as criterion in fish taxonomy.     

Parasitological diversity of the common goby, Pomatoschistus microps (Krøyer, 1838), in estuarine systems along the Portuguese coast

Parasitological diversity of the common goby Pomatoschistus microps along the Portuguese coast was studied based on samples collected using beam trawls in five coastal estuaries (Ria de Aveiro, Tagus, Sado, Mira and Guadiana estuaries) between May and July 2006. The classes Digenea, Cestoda, Nematoda and phylum Mastigophora were found, with Digenea Cryptocotyle sp. and Lecithochirium musculus being the most abundant taxa. Prevalence and mean abundance of Cryptocotyle sp. were highest in Ria de Aveiro (74%) and Mira estuary (28.05), respectively, whereas L. musculus values of both indices were highest in Sado estuary (prevalence = 64%; mean abundance = 11.77). Values varied along the Portuguese coast; the discriminant analysis based on the number of parasites showed some overlap between estuaries, although successfully separating the Sado and Mira estuaries. Overall, variations in estuaries were explained by different environmental pressures, leading to differences on host abundance and life-history of the parasites. Feeding behaviour and habitat selection therefore play a crucial role in shaping the biology, ecology and parasite assemblages of the common goby along the Portuguese coast.     

Reproductive effort and efficiency in the female common goby, Pomatoschistus microps (Krøyer) (Teleostei: Gobioidei)

Reproductive effort and efficiency are terms which together help to describe the reproductive investment of spawning fish. In this paper they are applied to a small and abundant inshore fish, the common goby, Pomatoschistus microps (Kroyer), based on data collected from the wild, and by modelling likely breeding patterns. Wet calorimetry was used to determine the energy content offish tissue, and this allowed reproductive effort to be expressed as both an energy and a weight ratio of gonad to somatic body. The gonadosomatic index (GSI) calculated as an energy ratio was greater than that calculated as a dry weight ratio. For ripe females the GSI (dry weight) at the onset of breeding was 67.5%. Theoretical and observed values of the maximum number of egg batches laid by a single female during a 16-week breeding season are 9-10, and this corresponds to a total caloric investment of almost 12 kJ. Estimates of the reproductive efficiency, using the dietary energy content during the breeding season, range from 28.2% to a maximum of 44.0%. These values are among the highest calculated for a fish species, and are in keeping with the long and intensive breeding strategy observed in the wild population.     

Phosphoglucose isomerase polymorphism in the common goby, Pomatoschistus microps (Krøyer) (TeleosteirGobiidae), around the British Isles

Phosphoglucose isomerase (PGI) polymorphism has been investigated by horizontal starch-gel electrophoresis in the common goby, Pomatoschistus microps (Krøyer), from 21 localities around the British Isles and at Roscoff, France. Sixteen PGI phenotypes were observed, consistent with occurrence of four alleles at each of the two loci (A,B). In the Teign estuary at Shaldon, Devon, seasonal fluctuation in PGI-A allele frequencies was accompanied in some months by departure from Hardy-Weinberg equilibrium. At this locality, a significant change in PGI-A allele frequencies was found with increasing modal age of sample (within a year class) but not between year-classes over eight years. Similar stability is noted for other areas. Major alleles (PGI-A2, A3; PGI-B2, B3) were found at all localities, but with marked differences in proportions. Atlantic coast populations tended to have higher A2 and B2 frequencies than those of the North Sea and English Channel, with Irish Sea populations having high A2 but low B2. Historical and selective causes for this geographical variation are discussed. A significant correlation exists between the frequencies of the major PGI-A alleles and maximum monthly mean sea temperature for the same area.     

Alkaline phosphatase activity in the skin of the Common goby, Pomatoschistus microps (Krøyer), in relation to cycles in scale and body growth

A histochemical study of the distribution of alkaline phosphatase in the skin of the Common goby, Pomatoschistus microps , showed that the enzyme is present in the dermis, not in the epithelium, and is more pronounced around the growing edge of the scale and below the fibrillary plate. The intensity of the enzyme reaction is higher in regenerated scales. In conjunction with the phenology of P. microps , a method was adopted to measure the enzyme activity in the skin, including scales, for successive months over a period of two years. Enzyme activity displayed seasonal fluctuations which were closely related to both body and scale growth. Enzyme activity also reflected other phenological cycles during the life-span of P. microps .     

Age-structure and life-span in the Common goby, Pomatoschistus microps

Age-structure and longevity in the euryhaline Common goby, Pomatoschistus microps (Krøyer), has been studied by monthly sampling of estuarine and shore populations in the Isle of Man and in collections from other parts of the British Isles. Age of individuals was determined by examination of caudal peduncle scales, where time of annulus formation was confirmed from monthly changes in mean terminal sclerite width and in frequency of scale-types. After the first winter of life, an annulus of narrow sclerites is produced on resumption of growth in spring and a separate summer annulus, corresponding with a growth retardation during the peak breeding season, is laid down usually in June. Maximum age did not exceed 21–26 months, with most adult fishes dying in the second autumn of life a few months after their first breeding season (within possible age-limits of 12–20 months). Seasonal migration is discussed with reference to the downstream movement of estuarine P. microps when sexually mature after the first winter of life, the winter distribution relative to temperature, and the preference of newly demersal young for less saline parts of the estuary. Cases of mortality from predation and environmental extremes are listed. The question of senescence in relation to life-history pattern and survival in P. microps and some other teleosts is discussed with special reference to gonad maturation and spawning, and the attainment of limiting size.     

Myxobolus albi n. sp. (Myxozoa) from the Gills of the Common Goby Pomatoschistus microps Krøyer (Teleostei: Gobiidae)

ABSTRACT. A recent investigation into the myxozoan fauna of common gobies, Pomatoschistus microps , from the Forth Estuary in Scotland, revealed numerous myxosporean cysts within the gill cartilage. They were composed of polysporous plasmodia containing myxobolid spores that were morphologically different from the other known species of Myxobolus and from the myxosporeans previously recorded from this host (i.e. the ceratomyxid Ellipsomyxa gobii , infecting the gall bladder, and the kudoid Kudoa camarguensis , infecting the muscle tissues). Spores were ovoid, 9.4 × 9.1 μm with a thickness of 6.6 μm, with two pyriform polar capsules, the polar filaments of which had four to five turns. Molecular analysis of the parasite's small subunit rDNA region, based upon a contiguous sequence of 1,558 base pairs, discriminated it from other myxosporean species that have been characterized so far. A comparison of the spore morphology and the molecular sequences determined for this new isolate with other myxozoans described to date, confirmed its identity as a previously unknown myxobolid supporting the proposal that this isolate be elevated to the species level as a new species within the genus Myxobolus . A phylogenetic analysis places this new myxobolid, Myxobolus albi n. sp., in a basal position of a clade containing the majority of Henneguya spp. sequenced to date and various Myxobolus spp.     

Studies on scale regeneration in the Common goby, Pomatoschistus microps (Pisces)

The longevity of original scales and the process and consequences of scale regeneration in the euryhaline Common goby, Pomatoschistus microps (Kroyer), has been studied by monthly sampling of two populations. Scale regeneration comprises four stages: formation of a new growth centre, a regenerated area in the form of a wide central irregular area lacking concentric circuli: formation of short and widely spaced circuli at the outermost region of the regenerated area: a check in regenerated scale growth on reaching the size of the original scales: and the commencement of normal growth similar to that of the surrounding original scales. Growth of regenerated scales within 30 days was not sufficient to attain the same size of the original ones. The average percentage of regenerated scales in successive months during the life span of P. microps is about 20% in immature fish and sharply increases up to about 60% of the total scales during the breeding season. The correlation between sharp increases in regenerated scales and the breeding season is also confirmed on examining scales from two other gobioid species, Gobius paganellus and Gobius cobitis. It is suggested that the loss of a large number of scales may result in the check in body growth during the breeding season.     

Phylogeography of the common goby, Pomatoschistus microps, with particular emphasis on the colonization of the Mediterranean and the North Sea

The phylogeographical patterns of a small marine fish, the common goby, Pomatoschistus microps, were assessed at 12 sites along the northeastern Atlantic coasts and the western Mediterranean Sea. A combination of two genetic markers was employed: cellulose acetate allozyme electrophoresis (CAGE) and sequence analysis of a 289 bp fragment of the mitochondrial locus cytochrome b. Both markers were congruent in revealing significant differences between samples (global FST = 0.247 for the allozymes and PhiST = 0.437 for the mitochondrial DNA data) and a pattern of isolation-by-distance. Phylogeographical analyses yielded a shallow branching structure with four groups. Three of those were confined to the Atlantic basin and showed a star-like pattern. The fourth group contained a central haplotype occurring at the edges of the species' distribution, accompanied by a few more rare variants, which were restricted to the Mediterranean Sea. A genetic break was observed around the British Isles, with distinct haplotypes dominating at either side of the English Channel. A significantly negative correlation between the degree of genetic diversity and latitude was recorded both for mitochondrial DNA (mtDNA) and allozymes in the Atlantic basin. Gene flow analysis suggested that recolonization of the North Sea and the coasts of western Scotland and Ireland may have taken place from a glacial refugium in the Southern Bight of the North Sea. These results are discussed in the perspective of possible postglacial migration routes of marine fish along the northeastern Atlantic coasts.     

Female preference for preferred males is reversed under low oxygen conditions in the common goby (Pomatoschistus microps)

Female preference for males that already have eggs in theirnest has beenreported in many fish species. The presence ofeggs may provide a cue forcopying the choice of previous femalesand may indicate that high-quality carewill be available. Consistentwith a review of 13 studies, we found thatfemale common gobies(Pomatoschistus microps) preferred to spawn withmales thathad already been chosen by females and whose nests thereforealreadycontained eggs. However, this preference was reversed underconditionsof low dissolved oxygen. We would not expect thisreversal if the secondfemale were using eggs as a signal ofmale genetic attractiveness to otherfemales unless the benefitswere outweighed by direct selection. The reversalalso couldnot be explained by differences in active courtship by males,ascourtship rates did not differ under low oxygen between maleswith or withouteggs. Low oxygen conditions corresponded witha nearly threefold increase inmale ventilation of eggs anda reduction in time spent near a selectingfemale. The reversalis therefore most likely due to females avoiding malesthatwould be unable to meet the demands of care of a second clutchunder lowoxygen conditions. Thus, an abiotic feature of theenvironment revealsplasticity of female choice, consistentwith hypothesized changes in benefitsof mating with preferredmales.     

Structure,growth and production of a remarkably abundant population of the common goby,Pomatoschistus microps (Actinopterygii: Gobiidae)

The common goby, Pomatoschistus microps, is a relevant species from estuarine food webs, playing important roles as predator of polychaetes and crustaceans and as prey for larger fishes and crustaceans. The Minho estuary (NW Portugal) is a relatively well-preserved and productive system. To assess the population structure and production of P. microps in this estuary, monthly samples were undertaken in three different areas along an estuarine gradient in the lower estuary. The density of P. microps varied considerably among seasons and sampling stations, with higher densities occurring in summer and autumn. The lowest densities were found closer to the sea. In general, the density of females was higher than the density of males in all sampling stations, while juveniles were more abundant within a salt marsh area. Compared with other European estuaries, our data showed a remarkable higher density and production values of P. microps. This may be related to the high freshwater input and the low salinities found in this estuary. In addition, we hypothesize that the lower density of the sympatric species P. minutus and the high availability of bivalve shells observed in the Minho estuary may have also contributed to the present results, once P. minutus and P. microps often display a diet overlap and the bivalve shells are crucial for the common goby reproduction.     

Long-term monitoring on the occurrence of a myxosporean parasite Kudoa camarguensis (Myxosporean) on the common goby (Teleostei, pisces) Pomatoschistus microps.

The evolution of a host-parasite system composed of Pomatoschistus microps-Kudoa camarguensis was investigated in the Vaccarès lagoon (Rh?ne river Delta, France) from 1993 to 1997. During this long-term monitoring, centennial flooding of the Rh?ne river occurred, leading to an inrush of about 110 million m3 of freshwater in the Vaccarès lagoon. The salinity drastically dropped from 14 to 5 g l(-1) in 1 wk. We observed that the annual prevalence and abundance of the myxosporean parasite decreased from 12.18 in 1993 to 3.7% in 1997 and from 1.10 in 1993 to 0.27 in 1997, respectively. Here, we discuss the possible reasons for the rapid decline of this host-parasite system following the flood.     

Genetic variation of Sebastes viviparus Krøyer in the North Atlantic

As part of a more extensive study on the inter- and intraspecific genetic variation of redfish, genus Sebastes , a total sample of 593 individuals of the species Sebastes viviparus were collected from several locations in Norwegian waters and off the south-west coast of Iceland. Haemoglobin and five polymorphic enzymes were analysed. A new haemoglobin polymorphism was observed, and unique alleles were found in Icelandic and Norwegian samples. The results of the enzyme analyses were largely consistent with previous results, but interpopulation variation was observed in the frequencies of IDHP * and Hb * alleles. S. viviparus displayed higher similarity with S. fasciatus from the West Atlantic than with the other Sebastes species.     

First record of Kudoa (Myxosporea) in Pomatoschistus microps in the Rhône Delta, France

Myxosporidiosis due to Kudoa sp. has been recorded in gobies Pomatoschistus microps , collected from the Etang du Vaccarès (Rhône Delta, France).     

Asymmetry, reproductive success and parasitism of Pomatoschistus microps in a French lagoon

There was an allometry between length of nesting male Pomatoschistus microps and the size of the nest. There was also a positive relationship between parasite load and pectoral fin asymmetry. There was no marked relationship between the number of eggs in the nest and parasitism or level of asymmetry. These results are discussed in terms of energy allocation and fish reproductive success.     

Water turbidity by algal blooms causes mating system breakdown in a shallow-water fish, the sand goby Pomatoschistus minutus

Eutrophication as a result of human activity has resulted in increased algal blooms and turbidity in aquatic environments. We investigated experimentally the effect of algal turbidity on the mating system and sexual selection in the sand goby, Pomatoschistus minutus (Pallas), a marine fish with a resource-defence mating system and paternal care. Owing to male-male competition and female choice, large males can monopolize multiple mates, while some males do not achieve mating at all. We show that the number of eggs laid was the same in both turbid and clear tanks but that mating success was more evenly distributed among males in turbid than in clear water. The opportunity for sexual selection was lower in turbid conditions. In turbid conditions mating success was less skewed towards large males. Our results suggest that increased turbidity can change mating systems and decrease the opportunity for sexual selection as well as selection intensity.     

Behaviour and success of sneaker males in the sand goby, Pomatoschistus minutus

In this study we investigated in laboratory conditions the presence of alternative reproductive tactics in the sand goby and describe proximate factors affecting their expression and success. We describe the reciprocal interactions of resident males, females, and sneaking males. The pre-spawning phase proved to be important for successful nest intrusions by sneakers. The number of sneakers had no effect on the frequency of successful intrusions. When small males had exclusive access to nest sites, they built a nest and courted females, showing a full behavioural repertoire. The intensity of courtship was, however, strongly positively correlated with body size. Using microsatellite DNA markers we assessed paternity shares of territorial and sneaker males in a subset of all replicates. Following successful nest intrusion sneaker males fertilised 5–10% of the eggs. Our interpretation of the results is that sneaking in the sand goby is a conditional tactic, one that is less successful than the normal nest guarding behaviour, at least for one spawning event. Received in revised form: 9 March 2001 Electronic Publication     

Gross structure and dimensions of the gill in an air-breathing estuarine goby,Pseudapocryptes lanceolatus

The gills of the air-breathing estuarine goby,Pseudapocryptes lanceolatus, are reduced owing to the development of a specialized organ of O₂ uptake from air. In the first gill arch, the filaments of the outer hemibranch are reduced to nearly one-half in comparison to those of its inner hemibranch. A smaller number of secondary lamellae per mm (27.6) occurring on one side of the gill filament reduces the gill surface area. A bilogarithmic plot of the gill area and the body weight indicates a curve with two significantly different components, one (b = 0.924) related to the fish weighing up to 6 g and the other (b = 0.405) to the fish weighing 8 g and above.     

Widespread endocrine disruption and reproductive impairment in an estuarine fish population exposed to seasonal hypoxia

The long-term effects on marine fish populations of the recent increase worldwide in the incidence of coastal hypoxia are unknown. Here we show that chronic environmental exposure of Atlantic croaker (Micropogonias undulatus) to hypoxia in a Florida estuary caused marked suppression of ovarian and testicular growth which was accompanied by endocrine disruption. Laboratory hypoxia studies showed that the endocrine disruption was associated with impairment of reproductive neuroendocrine function and decreases in hypothalamic serotonin (5-HT) content and the activity of the 5-HT biosynthetic enzyme, tryptophan hydroxylase. Pharmacological restoration of hypothalamic 5-HT levels also restored neuroendocrine function, indicating that the stimulatory serotonergic neuroendocrine pathway is a major site of hypoxia-induced inhibition. Inhibition of tryptophan hydroxylase activity to downregulate reproductive activity could have evolved as an adaptive mechanism to survive periodic hypoxia, but in view of the recent increased incidence of coastal hypoxia could become maladaptive and potentially affect fish population abundance and threaten valuable fishery resources.     

Sex ratio in the pelagic copepods Temora stylifera Dana and Centropages typicus Krøyer

From the study of several plankton samples from the surface of southern Aegean Sea it is found that the sex ratio in Temora stylifera Dana and Centropages typicus Krøyer varies considerably (from 40 % to 132 % for Temora and from 24 % to 178 % for Centropages). The mean sex ratio shows a seasonal fluctuations. For these species the highest sex ratio is observed during the period of greatest abundance, that is when the environmental factors are optimal for the species, and the minimum sex ratio during the period of minimum abundance. During the latter period there are adverse environmental factors and a scarcity of food; a large number of females and hence high fecundity will favour the survival of the species.