Comparative persistence of marine fish larvae from pelagic versus demersal eggs off southwestern Nova Scotia,Canada

Two groupings of larval fish were repeatedly identified by principal component analyses of larval densities from four broad-scale surveys during the spring and summer of 1985–1987 off southwestern Nova Scotia, Canada. Larvae originating from pelagic eggs (four species within Gadidae and Pleuronectidae) constituted one group, which were uniformly distributed over the sampling area with densities not correlated with bathymetry, although nearly all spawning occurs on the shallow western cap of Browns Bank, 100 km offshore. Larvae from demersal eggs (five species within Pholidae, Stichaeidae, Cottidae, Agonidae) constituted the second group, which dominated the shallow-water environments both inshore and on Browns Bank. Lower patchiness indices were evident amongst larvae from pelagic eggs in small and large sampling-gear collections (average 3.4 and 3.1, respectively) compared to fish hatching from demersal eggs (average 5.1 and 4.6). Fine-scale nearshore surveys over a 5 wk period in 1987 also showed that larvae of demersal eggs had a less variable distribution along an inshoreoffshore transect. Larvae from demersal eggs appear spatially persistent through the release of well-developed larvae from non-drifting eggs. These conclusions are consistent with other studies over a range of spatial scales in temperate and tropical environments, demonstrating that single-species models of larval dispersal are inadequate to account for the distributional patterns of larval fish in general.     

Sensory brain areas in three families of deep-sea fish (slickheads, eels and grenadiers): comparison of mesopelagic and demersal species

The sensory brain areas of a sample of <100 deep-sea fish species were studied, and the relative volumes of the olfactory bulb, optic tectum, octavolateral area and gustatory area were determined. In the absence of direct observations on the behaviour of this ichthyofauna these data allow deductions to be made about the kinds of sensory modalities used preferentially in the deep-sea environment. Here, members of three families are compared that have representatives living on or near the sea floor (“demersal”) and in the open water between 200 and 1.000 m (mesopelagic). The findings indicate that both regions present fish with rich and diverse sensory environments. While vision emerges as the dominant sense of the mesopelagic realm, olfaction seems more important on or near the bottom of the sea. However, other sensory modalities supplement these senses in species-specific patterns. Considerations of the phyletic relationships indicate different degrees of pervasiveness. Whilst in slickheads the dominance of vision appears to be a family-related trait, a similar relationship is not found in either eels or grenadiers. By contrast, the common trait in these two families seems to be the greater adaptability to the environment. Published online: 21 August 2002     

Muscle structure and differentiation in pelagic and demersal stages of the Antarctic teleost Notothenia neglecta

The distribution and fine structure of muscle-fibre types has been determined for the pelagic fingerling and demersal adult stages of the antarctic teleost Notothenia neglecta Nybelin, collected from Signy Island, Antarctica, between January and February 1984. In both stages, the pectoral fin adductor muscle (m.ad.p) is largely composed of slow fibres which contain abundant mitochondria (34 to 36%). During development, the ratio of capillaries to fibres increases less than does fibre diameter, so that capillary density is significantly lower in the m.ad.p of adults (498 mm^-2) than fingerlings (1 727 mm^-2). The secondary metamorphosis from a pelagic to a demersal mode of life is associated with the disappearance of subcutaneous lipid sacs and major changes in the distribution and structure of muscle fibres in the myotomes. The trunk cross-section of adult fish is almost entirely composed of poorly vascularised fast-muscle fibres (100 capillaries mm^-2), which contain densely packed myofibrils (86.3%), and have few mitochondria (1.4%). Slow-muscle fibres in adults are restricted to a thin wedge adjacent to the lateral line canal. In contrast, slow fibres occur around the entire circumference of the trunk in fingerlings representing 24% of the total cross-sectional area at the post-anal level. Volume densities (%) of mitochondria, intracellular lipid and myofibrils in this tissue are respectively 37.0, 7.9, 38.6 for fingerlings and 13.1, 0, 70.3 for adults. Slow-muscle fibres in adult fish are of unusually large diameter (50 to 120 m) and have relatively low capillary densities (266 mm^-2). These morphological changes reflect a general decrease in activity and a shift from a sub-carangiform to a labriform mode of swimming following transition from the fingerling to adult stage of the life cycle. The results are briefly discussed in relation to the physiology and ecology of antarctic fish.Please address all correspondence and requests for reprints to Dr. I.A. Johnston     

Effects of periodic hypoxia on distribution of demersal fish and crustaceans

Effects of periodic hypoxia (O₂ < 2 mg l^–1) on distribution of three demersal fish species, spot (Leiostomus xanthurus), hogchoker (Trinectes maculatus) and croaker (Micropogonias undulatus), and of two crustacean species, mantis shrimp (Squilla empusa) and blue crab (Callinectes sapidus), were investigated in the lower York River, Chesapeake Bay, USA. Trawl collections were made in four depth strata (5 to 10, 10 to 14, 14 to 20 and > 20 m) during normoxia and hypoxia from 26 June to 20 October 1989. Three periods with hypoxia in the bottom water (below 10 m depth) occurred in mid-July, early August and early September, each with a duration of 6 to 14 d. The demersal fish and crustaceans studied were all affected by hypoxia, and a general migration from deeper to shallower water took place during July and August. However, when oxygen conditions improved after a hypoxic event all species, exceptS. empusa, returned to the deeper areas. The degree of vertical migration was related to levels of oxygen concentration and varied for the different species.M. undulatus was the most sensitive species to low oxygen, followed byL. xanthurus andC. sapidus. T. maculatus andS. empusa were more tolerant and survived in 14 to 25% oxygen saturation by increasing ventilation rate and, forS. empusa, by also increasing blood pigment (haemocyanin) concentration. Periodic hypoxia driven by the spring-neap tidal cycle may represent a natural phenomenon with which the fishes and crustaceans are in a delicate balance. Areas experiencing periodic short-lived hypoxia may be good nursery grounds for fisheries species, and there is no indication that the habitat value in the study area of lower York River is lessened. However, if eutrophication lengthens the time of hypoxia or brings the system closer to anoxia the system may change and become characteristically stressed. The migratory and physiological responses of these species to hypoxia are good indicators of the severity of oxygen stress and could be used as part of an early warning monitoring system for changes in environmental quality.Contribution of the Virginia Institute of Marine Science     

Theoretical analysis of the weight-length relationship in fish juveniles

The weight-length relationship in fish juveniles was investigated theoretically, to assess the significance of the allometric factor and the validity of the condition factor; these biological factors often remain undetermined, because most fishery studies have been conducted for commercial-sized and/or adult populations. The exponent b (allometric factor) seemed to be the main parameter, performing a key role in the equation W=aL ^b , where W=weight, a is a constant and L=length. The parameters a (condition factor) and K (ponderal index; K=10³ W/L ³) were judged to be less important in comparative studies, since these parameters were closely correlated with b. It is recommended that the assumed theoretical value of b=3 not be used in applied ichthyological surveys, since this value was rarely obtained in the studies, and since a much wider range is usually seen. These analyses led to a new working hypothesis — not yet verified — which opens a new approach to understanding the biological significance of the allometric factor. This approach involves the fractal theory (where b may be considered as a fractal dimension equivalent) linked to the theory of saltatory ontogeny [where b is a threshold characteristic in the (early) life history of fishes].     

Phosphorus metabolism and water uptake during final maturation of ovaries of teleosts with pelagic and demersal eggs

An earlier study showed large changes in ovarian phosphoprotein, a characteristic component of vertebrate yolk, during post-vitellogenic meiotic maturation (ripening) of ovaries of teleosts with pelagic eggs. Here, the study of four phosphorus-containing ovarian fractions is extended to other teleost families with pelagic eggs and to species with demersal eggs. Fishes were caught in the sea and lakes of western Scotland between 1982 and 1984. In the codGadus morhua, spratSprattus sprattus, dragonetCallionymus lyra, Norway poutTrisopterus esmarkii, saithePollachius virens, lingMolva molva and flounderPlatichthys flesus, all of which spawn pelagic eggs, the massive water influx during ripening which renders the eggs buoyant was accompanied by large changes in yolk phosphoprotein which were apparent as decrease or disappearance of protein phosphorus as conventionally determined. During ripening of the demersal eggs of the herringClupea harengus, both the water uptake and the decrease in protein phosphorus were less pronounced. In the three-spined sticklebackGasterosteus aculeatus, sea sticklebackSpinachia spinachia, sand gobyPomatoschistus minutus and perchPerca fluviatilis, little or no changes in water content or protein phosphorus both usually increased in species with pronounced water uptake and decreased in species with little or no water uptake. Lipid phosphorus showed little change in all species examined except herring, in which it increased. It is concluded that the characteristic changes in phosphoprotein and other phosphorus-containing fractions are most pronounced in species with pelagic eggs exhibiting massive water uptake on ripening, but are found to a lesser extent in species with demersal eggs in which considerable water uptake accompanies ripening.     

Rapid changes in growth,condition, size and age of small pelagic fish in the Mediterranean

Since 2007, the ecosystem of the Gulf of Lions has shifted to a different regime, characterised by a low anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) biomass and a remarkably high sprat (Sprattus sprattus) biomass. Surprisingly, the abundance and recruitment of anchovy and sardine remained high. To understand which processes (bottom-up or top-down control, etc.) could have caused this shift, we studied the changes in body condition, growth and size and age of anchovy, sardine and sprat over 1984–1985 and 1992–2012, using data from scientific surveys. The annual age structure of anchovy and sardine was estimated using Bayesian mixture models based on size frequency data with priors on the age–length relationship derived from independent otolith readings. The results indicated periods during which anchovy and sardine were in an average (1992–2004), good (2005–2007) or poor (2008–2012) overall state of condition. For sardine, the shift towards smaller fish observed during these past 4 years was explained by a combination of slower growth and the disappearance of older individuals (ages 2+). Despite the increase in biomass of sprat since 2008, indications were found that sprat was also smaller than in the past. As growth and condition decreased and overexploitation has not been documented or suspected for those three species in this area, we propose that the current decline in sardine and anchovy biomass could be due to qualitative and/or quantitative modifications in the planktonic production (i.e. a bottom-up control) or mass mortalities of adults due to an epidemic disease.     

Benthic and pelagic fish biomass of the upper continental slope off eastern Tasmania

Benthic and pelagic fishes were sampled east of Maria Island, Tasmania, at two-monthly intervals from April 1984 to June 1985, from the surface to the bottom (500 m depth), using commercial-sized trawls. Biomass was calculated by the area swept/volume filtered method and divided by estimated catchability coefficients so that catches from the two sampling gears could be combined. Of the 54 families caught, three (Myctophidae, Squalidae, Sternoptychidae) contributed 25% of the 115 species. Most benthic and dispersed species were caught regularly, whereas most pelagic species occurred only occasionally and in low numbers, although a core group was always present. Total fish biomass was high (range=77 to 532 g m^-2; x= 390 g m^-2), due almost entirely to the myctophid Lampanyctodes hectoris (over 90% of the biomass). Benthic biomass was relatively low and stable, but derived from many species. Pelagic biomass was high, fluctuated widely and was composed of a few species. Biomass was highest in summer: Maurolicus muelleri increased by a factor of 200, Diaphus danae by 50, and L. hectoris, Macruronus novaezelandiae and Lepidorhynchus denticulatus by almost 10. Peaks in biomass may correlate with the interactions of the subtropical convergence and the East Australian Current and the resultant marked seasonal cycle in water temperature, nutrients and primary productivity.With an appendix by T.J. Kenchington, CSIRO Division of Fisheries, Hobart, Tasmania 7001, Australia     

Reconstructing the movements of free-ranging demersal fish in the North Sea: a data-matching and simulation method

Demersal fish cannot be readily tracked using data loggers that provide satellite-based or light-based geolocation. Moreover, fish that are highly mobile within the water column cannot readily be located with other methods, such as the tidal location method (TLM). As an alternative, we describe a process that provides estimates of geographic location by simulating movement paths through geographic locations that match temperature and depth data recorded by data loggers. Depths and temperatures recorded by data loggers were compared with a North Sea temperature and depth database to identify all locations with matching data. A movement rate filter was then applied to eliminate spurious locations and simulations of possible movement paths through the remaining positions were used to generate estimates of the likelihood of a particular location having been occupied. The performance of the technique was assessed by reconstructing movement paths of artificial migrations and by using depth and temperature data collected at known locations in the North Sea. Estimates of the positional accuracy and error were comparable to the North Sea TLM. Reconstructions of the migrations of cod tagged and released in the North Sea were successfully achieved with the method. This method has application in defining the movements and migrations of commercial species in any sea area where databases of commonly measured environmental variables are available.     

Spatial and temporal changes in the demersal fish community of the Ria de Arosa (NW Spain)

The demersal fish community was sampled seasonally in three habitats (beach, raft and middle) of the inner, middle, and outer Ria de Arosa (NW Spain). A total of 73 species of demersal fish, dominated by the family Gobiidae, were found. There were no important seasonal changes in abundance, with similarity values always higher than 60% between samples from two different sampling periods. Raft stations in the ria show the highest values of abundance all year, containing almost 1 individual m^-2 in winter. The highest diversity indices were those from beach areas (2.11 to 2.27) and the lowest ones those from middle areas (1.13 to 1.86). Similarity indices and factorial analysis revealed three major groupings of species and samples, related to water depth and nature of the bottom.     

Biodiversity and species–environment relationships of the demersal fish assemblage at the Great Meteor Seamount (subtropical NE Atlantic), sampled by different trawls

Quantitative data collected with different bottom trawls at the Great Meteor Seamount (subtropical NE Atlantic, 30°N; 28.5°W) in 1967, 1970 and 1998 are compared. Bootstrap estimates of total catch per unit effort increased from 6.96 and 10.8 ind. m^-1 h^-1 in 1967 and 1970, respectively, to 583.98 ind. m^-1 h^-1 in 1998. Gear effects and an effect of gear over time accounted for 47.1% and 20% of species variability. Further significant factors were time of day and habitat, while season was not significant. A total of 43 species was collected. Including supplementary species information, a grand total of 46 species was found associated with the Great Meteor Seamount. Diversity was higher in 1967 and 1970 (Shannon's diversity: H'=2.5 and 1.6) than in 1998 (H'=0.9). Species-environment relationships are discussed in terms of a sound-scattering layer-interception hypothesis, i.e. utilisation of prey from a diurnally moving sound-scattering layer for the bentho-pelagic community. This is probably augmented by concentration effects in a circular current around the seamount (Taylor-column). Long-term changes are discussed with respect to a decrease in biodiversity due to considerable increases in Macroramphosus scolopax and Capros aper. In 1998, the increase of abundance of Trachurus picturatus and the respective decreases for genuine benthic species were likely to have been caused by a change of gear.     

Changes in species composition of demersal fish fauna of Southeast Gulf of Carpentaria,Australia, after 20 years of fishing

The changes in a tropical demersal fish community in the southeast Gulf of Carpentaria, Australia, were examined by comparing the results of a survey undertaken in 1964 before the area was fished, with two surveys in 1985 and 1986 after 20 yr of commercial trawl fishing. The numerical abundance of 52 of the 82 fish taxa had not changed significantly, but that of 18 had decreased while 12 had increased. One taxon (Paramonacanthus spp.) had decreased by more than 500 times and another (Saurida micropectoralis) had increased substantially in abundance. The changes occurred throughout the area surveyed, but the largest changes were offshore. In the pre-trawling community most taxa were caught mainly during the night, while in the post-trawling community most were caught in the same numbers during day and night. In 10 of the 30 taxa that changed in abundance, changes were within a family and could not be explained. For the remaining 20, the changes could be related to their position in the water column: benthic taxa decreased and bentho-pelagic taxa increased. The changes were assessed in relation to fishing effort, and changes in the mud content of the substrate in the study area. Although the changes did not correlate with the fishing effort among three zones in the study area, it is suggested that fishing effort and discarding of the by-catch caused the change in 18 taxa. The magnitude of the decreases of some species might be related to changes in the sediment or possibly other long-term environmental change. There was also a change in the diel behaviour in the fish community that perhaps may be related to the effects of fishing on a tropical multispecies fish community.     

Food resource partitioning in a Mediterranean demersal fish assemblage: the effect of body size and niche width

We investigated the effects of body size, feeding strategy and depth distribution on the trophic resource partitioning among the 26 dominant fish consumers in a fish assemblage on the central Mediterranean shelf-break. The fish assemblage was structured in two major trophic guilds: epibenthic and zooplanktonic feeders, according to the position of each predator along the benthos–plankton gradient. Within each main guild, the species were segregated along a prey-size or fish-size gradient into five further guilds. Fish size and prey size were strongly correlated, indicating that the prey-size niche can be well explained by predator size. Fish consumers showed a significant negative correlation between the similarity in prey type and the similarity in depth distribution; most species with similar trophic preferences segregated along the depth dimension. The only predators overlapping in both food and depth preferences were those with a more specialist trophic behavior. These results suggest that fish body size and depth preferences are the two main niche dimensions, explaining a large part of the coexistence between the Mediterranean shelf-break fish consumers.     

Spatio-temporal structure of pelagic larval and juvenile fish assemblages in coastal areas of New Caledonia,southwest Pacific

This study aims at describing the diversity and composition of larval and juvenile fish assemblages in coastal areas of New Caledonia, southwest Pacific, and identifying the environmental factors that influence the seasonal and spatial patterns of these assemblages. A total of 97 taxa belonging to 7 orders and 26 familis were captured in three bays near Nouméa by light trapping every month between January 2002 and June 2003. The assemblages were dominated by Clupeiform larvae and juveniles (96.4% of total abundance) and followed by Perciform larvae (3%). The number of taxa per sample varied from less than five in July–August to more than ten in October–November and abundances followed the same seasonal pattern. Analyses of similarity showed significant differences in the assemblages caught in the three bays and analyses of contribution to the dissimilarity revealed that these differences were due to the most abundant families. The constant part of the relationship between environmental variables and the composition of assemblages was assessed by the partial triadic analysis STATICO, a statistical approach that takes into account the strong seasonality of the data. Rainfall, wind direction and thermal stratification of the water column were found to play a major role in the structure of the assemblages, although tidal amplitude and wind speed became important when Clupeidae and Engraulididae were excluded from the analyses. The richness, relative abundances and seasonal variations of the assemblages caught in three bays under study are close to what has been observed elsewhere in the tropics. This study shows the efficiency of the STATICO analysis for identifying the environmental factors that have a permanent effect on assemblages and sorting them out from those which act temporally or on specific locations. The high abundances and diversity of coral-reef fish larvae observed in coastal zones of New Caledonia suggest that further studies are needed to fully explore the role of the coastal zones of New Caledonia as nurseries.     

Distribution,abundance, and substrate preferences of demersal reef zooplankton at Lizard Island Lagoon,Great Barrier Reef

Demersal zooplankton, those plankton which hide within reef sediments during the day but emerge to swim freely over the reef at night, were sampled quantitatively using emergence traps planced over the substrate at Lizard Island Lagoon, Great Barrier Reef. Densities of zooplankton emerging at night from 6 substrate types (fine, medium, and coarse sand, rubble, living coral and reef rock) and from 5 reef zones (seaward face, reef flat, lagoon, back reef, and sand flat) were determined. A large population of nocturnal plankton including cumaceans, mysids, ostracods, shrimp, isopods, amphipods, crustacean larvae, polychaetes, foraminiferans and copepods are resident members of the reef community at Lizard Island. The mean density of plankton emerging throughout the reef was 2510±388 (standard error) zooplankton/m² of substrate. Biomass averaged 66.2±5.4 mg ash-free dry weight/m² of substrate. Demersal zooplankton exhibited significant preferences for substrate types and reef zones. The highest mean density of zooplankton emerged from coral (11,264±1952 zooplankton/m²) while the lowest emerged from reef rock (840±106 zooplankton/m²). The density of demersal plankton was six times greater on the face than in any other zone, averaging 7900±1501 zooplankton/m². Copepods dominated samples collected over living coral and rubble while foraminiferans, ostracods and decapod larvae were most abundant from sand. Plankton collected with nets at night correlated only qualitatively with plankton collected in emergence traps from the same location. Although abundant, demersal plankton were not numerous enough to meet the metabolic needs of all corals at Lizard Island Lagoon. Demersal plankton appear especially adapted to avoid fish predation. The predator-avoidance strategies of demersal plankton and maintenance of position on the reef are discussed. Our results indicate that much of the zooplankton over coral reefs actually lives on the reef itself and that previous studies using standard net sampling techniques have greatly underestimated plankton abundance over coral reefs.     

Comparative studies on the metabolism of shallow-water and deep-sea marine fishes. IV. Patterns of aerobic metabolism in the mesopelagic deep-sea fangtooth fish Anoplogaster cornuta

Measurements have been made of oxygen consumption rates O₂ of 10 specimens of the mesopelagic deep-sea fangtooth fish Anoplogaster cornuta. Determinations were made at 1 atm pressure, at temperatures of 3°, 7°, and 10°C, at dissolved oxygen concentrations ranging from near saturation to zero, with the fish swimming at low, controlled speeds. Weight-specific O₂ were uniformly low. They showed Q₁₀'s of 2.5 and 1.3, respectively, in the temperature ranges 3° to 7°C, and 7° to 10°C, at dissolved oxygen concentrations above 2 ml (standard temperature and presusure, STP)/1. Measurable O₂ continued in these fish at dissolved oxygen concentrations down to the lowest levels detectable with our instruments. At 7°C the average critical oxygen tension (P _c ) for the entire group was near 35 mm Hg. However, there is a statistically significant positive slope to the regression line relating O₂ to P _c for individual fish. The physiological and ecological significance of these results is discussed, particularly with reference to thermal effects and to the basis for survival by A. cornuta in the oxygen minimum layers of the eastern Pacific Ocean.     

Lethal effects of elevated pH and ammonia on juveniles of neotropical fish Colosoma macropomum (Pisces, Caracidae)

Ammonia is the main nitrogenous waste material excreted by gills, then is oxided first to nitrite and then to nitrate. The proportion of ionized-un-ionized ammonia depends on pH and temperature, when this variables increase in a solution containing ammonia the equation goes to left, so the proportion of NH3 increases and the solution becomes more toxic. The purpose of this study was to investigate the acute lethal effects of elevated pH and ammonia on tambaqui juveniles. With a constant ammonia concentration of 5.0 mg/l NH3, there was no mortality a pH of 6.0 (control) and 7.0; but was of 10-20% a pH of 8.0 and 100% at 9.0. The lethal effects of elevated pH and un-ionized ammonia should be recognized as a potential factor contributing to the variable success of tambaqui production ponds, but this species is highly resistant in comparison with other freshwater fish.     

Influence of salinity and temperature on the oxygen consumption in young juveniles of the Indian prawn Penaeus indicus

Routine oxygen consumption of very young juveniles (0.1 g) of Penaeus indicus H. Milne Edwards was significantly influenced by ambient temperature and weight of the animal, but not by ambient salinity, when tested at salinities (7, 21, and 35) to which they had been long-term (over 10 days) acclimated. Standard oxygen consumption of young juvenile prawns (1 to 3 g), subjected to step-wise changes in ambient salinity, from sea water to low salinity waters (2 to 6), and measured after short-term (24 h) salinity acclimation at each step, was lowest at salinities where prawns such as those tested occur naturally (10 to 15). The metabolic rates do not appear to have a direct relation to the osmotic gradient, even when the influence of interfering activity is eliminated. It appears that factors other than osmotic gradient will have to be sought in order to explain the metabolic patterns of P. indicus in relation to salinity.     

Oxygen uptake in relation to group size in the juveniles of a climbing perch, Anabas testudineus (Bloch)

The present work reports oxygen uptake in relation to group size in the juveniles (body weight: 0.70 to 1.30 g) of a climbing perch, Anabas testudineus (Bloch). The experiments were conducted at 21.5 +/- 1.0 degrees C using a cylindrical glass respirometer having continuous water flow system. With an increase in the number of fish at an interval of 5 from 5 to 40 in each fourth subsequent experiment, the weight specific aquatic oxygen uptake of a fish decreased from 0.192 +/- 0.030 to 0.800 +/- 0.006 ml O2 x g(-1)x(h(-1). When compared with a controlled fish, there was a reduction of 27.80% in the oxygen uptake in a group of 5 but 58.39% in a group of 40. A negative and significant correlation (r = 0.8411, p < 0.01) was calculated between oxygen uptake and group size of fishes. The investigation showed that probably due to shoaling behaviour, the aquatic oxygen uptake in the juveniles of A. testudineus always remained high in controlled fish or a fish in isolation than when they were in a group.