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Analysis of maximum depth of occurrence of 11 952 marine fish species shows a global decrease in species number ( N) with depth ( x; m): log10 N = −0·000422 x + 3·610000 ( r2 = 0·948). The rate of decrease is close to global estimates for change in pelagic and benthic biomass with depth (−0·000430), indicating that species richness of fishes may be limited by food energy availability in the deep sea. The slopes for the Classes Myxini (−0·000488) and Actinopterygii (−0·000413) follow this trend but Chondrichthyes decrease more rapidly (−0·000731) implying deficiency in ability to colonize the deep sea. Maximum depths attained are 2743, 4156 and 8370 m for Myxini, Chondrichthyes and Actinopterygii, respectively. Endemic species occur in abundance at 7-7800 m depth in hadal trenches but appear to be absent from the deepest parts of the oceans, >9000 m deep. There have been six global oceanic anoxic events ( OAE) since the origin of the major fish taxa in the Devonian c. 400 million years ago ( mya). Colonization of the deep sea has taken place largely since the most recent OAE in the Cretaceous 94 mya when the Atlantic Ocean opened up. Patterns of global oceanic circulation oxygenating the deep ocean basins became established coinciding with a period of teleost diversification and appearance of the Acanthopterygii. Within the Actinopterygii, there is a trend for greater invasion of the deep sea by the lower taxa in accordance with the Andriashev paradigm. Here, 31 deep-sea families of Actinopterygii were identified with mean maximum depth >1000 m and with >10 species. Those with most of their constituent species living shallower than 1000 m are proposed as invasive, with extinctions in the deep being continuously balanced by export of species from shallow seas. Specialized families with most species deeper than 1000 m are termed deep-sea endemics in this study; these appear to persist in the deep by virtue of global distribution enabling recovery from regional extinctions. Deep-sea invasive families such as Ophidiidae and Liparidae make the greatest contribution to fish fauna at depths >6000 m. [ABSTRACT FROM AUTHOR]

A time series from 1977-1989 and 2000-2002 of scientific trawl surveys in the Porcupine Seabight and adjacent abyssal plain of the NE Atlantic was analysed to assess changes in demersal fish biomass and length frequency. These two periods coincide with the onset of the commercial deep-water fishery in the late 1970s and the onset of the regulation of the fishery in the early 2000's, which allowed us to investigate changes in the relationship between total demersal fish biomass and depth between the pre- and post commercial fishing periods, as well as changes in the biomass (kg km-2) depth distribution and length frequency distribution of the most dominant fish species. Our results show a decline in total demersal fish biomass of 36% within the depth range of the commercial fishery (<1500m).Whilst there were significant declines in target (e.g. Coryphaenoides rupestris decreased by 57%) and non-target (e.g. C. guentheri and Antimora rostrata) species, not all species declined significantly. Changes in the overall length-frequency distribution were detected for 5 out of the 8 dominant species occupying depth ranges both within and outside the maximum depth for commercial trawling. This suggests that whilst there is evidence for likely fishery impacts on the biomass distribution of the demersal fish population as a whole, species-specific impacts are highly variable. It is clear that changes in population structure can extend beyond the depth at which fishing takes place, highlighting the importance for also considering the indirect effects on deep-sea fish populations. [ABSTRACT FROM AUTHOR]

A time series from 1977-1989 and 2000-2002 of scientific trawl surveys in the Porcupine Seabight and adjacent Abyssal Plain of the NE Atlantic was analysed to assess changes in demersal fish biomass and length frequency. These two periods coincide with the on-set of the commercial deep-water fishery in the late 1970s and the on-set of the regulation of the fishery in the early 2000's and allowed us to investigate changes in the relationship between total demersal fish biomass and depth between the pre- and post commercial fishing periods, changes in the biomass (kg km² ) depth distribution and length frequency distribution of the most dominant fish species. Our results show a decline in total demersal fish biomass of 36% within the depth range of the commercial fishery (<1500m). Whilst there were significant declines in target (e.g. Coryphaenoides rupestris decreased by 57%) and non-target (e.g. Coryphaenoides guentheri and Antimora rostrata) species, not all species declined significantly. Changes in the overall length-frequency distribution were detected for 2 species (Coryphaenoides armatus, Synaphobranchus kaupii ), but only at depths greater than 1800m (outside the maximum depth for commercial trawling). This suggests that whilst there is evidence for likely fisheries impacts on the biomass distribution of the demersal fish population as a whole, species-specific impacts are highly variable. It is clear that changes in population structure can extend beyond the depth at which fishing takes place, highlighting the importance for also considering the indirect effects on deep-sea fish populations. [ABSTRACT FROM AUTHOR]

study on the feeding ecology of juvenile cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus during the pelagic to demersal transition was carried out on fishes sampled throughout their settlement season at a local nursery ground in the north-western North Sea, off the Scottish east coast. A comprehensive quantitative taxonomic analysis of the diets, as described in the paper, showed the emergence of distinctive feeding niches, minimizing the potential for competition between species and size categories. The diet of the juveniles changed with fish size, water depth, time of year and distance offshore. Small G. morhua were present in the study area earlier in the season, settled further inshore and ate a higher proportion of pelagic prey (copepods) and as size increased they moved into deeper waters and targeted larger, more benthic prey. As M. aeglefinus grew larger and moved into deeper waters, a diet of largely copepods, amphipods, pelagic Ammodytes spp., cyprids and pelagic gastropods evolved to one dominated predominantly by fishes and benthic invertebrates. In the case of M. merlangus, widespread ages and sizes throughout the sampling season, a consequence of their more protracted spawning season, resulted in dietary changes which were more likely to be influenced by seasonal changes in the prey field, in addition to developmental (size) changes, than the diets of the other two species. [ABSTRACT FROM AUTHOR]

scavenging interaction between the arrow tooth eel Synaphobranchus kaupii and the Portuguese dogfish Centroscymnus coelolepis, both ubiquitous components of fish assemblages at bathyal depths, was observed. Using a baited camera between 1297 and 2453 m in the eastern Atlantic Ocean continental slope, it was shown that despite consistently rapid arrival times of S. kaupii (<5 min), their feeding bouts (indicated by acute peak in numbers) did not take place until shortly after C. coelolepis arrived and removed the exterior surface of the bait (skipjack tuna Katsuwonus pelamis carcass). Change in the numbers of S. kaupii was hence dependent on the arrival of a more powerful scavenger throughout the study site, and at the deeper stations where the population of C. coelolepis declined, S. kaupii was observed to be present but waited for >2 h before feeding, thus contradicting conventional scavenging assumptions in the presence of a food fall. [ABSTRACT FROM AUTHOR]

A baited imaging lander was deployed six times in the Nazaré Canyon at depths from 909 to 4361 m during August 2005 to investigate the demersal scavenging fishes. Species observed and lander-derived abundance estimates were similar to previous data from the Porcupine Seabight and abyssal plain, north-east Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Natural bioluminescence (that not mechanically stimulated by human intervention) produced by organisms on the seafloor of the northeast Atlantic ocean between 970 and 4,800 m depth was examined using an image intensifying (ISIT) camera mounted on an autonomous lander system. In the absence of bait little or no luminescence was observed but with bait present there was a significant inverse relationship with depth, Log10 (1 + number of events h−1) = 1.7627–0.3235 depth (km) ( r 2 = 0.8158, P < 0.001) indicating an average of 2.6 events h−1 at 4 km and 28 h−1 at 1 km. But in an area at ca . 1 km depth near carbonate and coral mounds the mean was 133 events h−1, much higher than predicted. In this bioluminescent hot spot 52–483 events h−1 were observed including moving luminescent targets and release of patches of luminescent material into the water around the bait so that on occasions the whole area around the bait was illuminated persisting on a time scale of minutes. At abyssal depths, luminescence was much less than reported at similar depths in the tropical NE Atlantic off Cape Verde. The sources of luminescence could not be determined but in the most active areas were associated with presence of eels Synaphobranchus kaupii which although themselves not luminescent may have stimulated luminescence from prey organisms such as ostracods ( Vargula norvegica). [ABSTRACT FROM AUTHOR]

Measurements of routine swimming speed, “tail-flip” escape responses, and oxygen consumptions were made of the deep-sea shrimpAcanthephyra eximiausing autonomous landers in the Rhodos Basin at depths of up to 4,400 m and temperatures of 13-14.5°C. Routine swimming speeds at 4,200 m averaged 0.18 m s-1 or 3.09 body lengths s-1, approximately double those of functionally similar oceanic scavengers. During escape responses peak accelerations of 23 m s-2 or 630.6 body lengths s-2 were recorded, with animals reaching speeds of 1.61 m s-1 or 34.8 body lengths s-2. When compared to shallow-water decapods at similar temperatures these values are low for a lightly calcified shrimp such asA. eximiadespite a maximum muscle mass specific power output of 90.0 W kg-1. A preliminary oxygen consumption measurement indicated similar rates to those of oceanic crustacean scavengers and shallower-living Mediterranean crustaceans once size and temperature had been taken into account. These animals appear to have high routine swimming speeds but low burst muscle performances. This suite of traits can be accounted for by high competition for limited resources in the eastern Mediterranean, but low selective pressure for burst swimming due to reductions in predator pressure. [ABSTRACT FROM AUTHOR]

Analysis of video recordings of swimming in abyssal grenadiers Coryphaenoides spp. revealed site differences in tail-beat frequencies. At the highly oligotrophic deep central North Pacific (CNP; 5800 m depth) station fishes had significantly lower tail-beat frequencies (0·73 ± 0·02 Hz, mean ± S.E.) than fishes of similar size at the shallower 'Station F' (Sta. F; 4400m depth) beneath the more productive waters of the California Current Upwelling (1·06 ± 0·04 Hz). These behavioural differences may be evidence for the proposed physiological adaptations of Coryphaenoides armatus and Coryphaenoides yaquinae, to different depths and food supply levels. At CNP, smaller fishes (38·9 cm mean L[sub T]) were present in autumn than in summer (59·4cm L[sub T]) suggesting large-scale migrations across the abyssal ocean floor despite the observed slow swimming speeds. [ABSTRACT FROM AUTHOR]

During January 2000 a baited video camera system was deployed fifteen times at depths of 719–1518 m around the Subantarctic island of South Georgia. Four species of lithodid (Anomura: Lithodidae) crab (Paralomis formosa, P. spinosissima, Lithodes sp., and Neolithodes diomedeae) were attracted to the baits of which Paralomis formosa was the most abundant. Using arrival rate at baits, predictions of odour plume size, and observations of walking speed the abundance of the stone crab, Paralomis formosa, was estimated. Numbers of crabs increased rapidly following bait emplacement, with total numbers observed in the 4.9 m2 field of view exceeding 50 within 200 minutes on three occasions. Current speed was used to predict the area of the odour plume, and by integrating the area to account for scavenger speed the effective area of the odour plume was obtained. The density of crabs, estimated from the increase in crab numbers per unit area of odour plume, averaged 8313 individuals km−2 (range 1100–25 600). Density was not significantly correlated with depth, temperature, or current speed and variability was attributed to substrate form. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

The evolution of chordate glutamic acid decarboxylase (GAD; EC 4.1.1.15), a key enzyme in the central nervous system synthesizing the neurotransmitter gamma-amino-butyric acid (GABA) from glutamate, was studied. Prior to this study, molecular data of GAD had been restricted to mammals, which express two distinct forms, GAD65 and GAD67. These are the products of separate genes and probably are derived from a common ancestral GAD following gene duplication at some point during vertebrate evolution. To enable a comprehensive phylogenetic analysis, molecular information of GAD forms in other vertebrate classes was essential. By reverse transcriptase-polymerase chain reaction (RT-PCR), partial nucleotide sequences of GAD were cloned from brains of zebra finch (Taeniopygia guttata), turtle (Trachemys scripta), goldfish (Carassius auratus), zebrafish (Danio rerio), and armoured grenadier (Coryphaenoides (Nematonurus) armatus, a deep-sea fish), and from the cerebral ganglion plus neural gland of Ciona intestinalis, a protochordate. Whereas GAD65 and GAD67 homologs were expressed in birds, reptiles, and fish, only a single GAD cDNA with equal similarities to both vertebrate GAD forms was found in the protochordate. This indicates that the duplication of the vertebrate GAD gene occurred between 400 and 560 million years ago. For both GAD65 and GAD67, the generated phylogenetic tree followed the general tree topology for the major vertebrate classes. In turtle, an alternative spliced form of GAD65, putatively encoding a truncated, nonactive GAD, was found. Furthermore, a third GAD form, which is equally divergent from both GAD65 and GAD67, is expressed in C. (N.) armatus. This third form might have originated from an ancient genome duplication specific to modern ray-finned fishes. [ABSTRACT FROM PUBLISHER]

Carotenoid pigment composition of sea lice (Lepeophtheirus salmonis) was compared in samples taken from wild salmon (Salmo salar L.) from the river North Esk and salmon fed on an artificial diet in a fish farm. Pigment was also extracted from sea lice egg strings. Two pigment peaks could be identified in the chromatograms (HPLC) — astaxanthin, normally considered characteristic of wild salmon, and canthaxanthin, the pigment fed to farm fish. The ratio of canthaxanthin-like pigment to astaxanthin (C:A ratio) was 45:1 in farm lice and 8:1 in wild lice. Carotenoid content therefore could potentially be used as a tracer of origin of sea lice in epidemiological investigations. Considerable variability of pigment concentrations in both farm and wild lice may make interpretation difficult. [ABSTRACT FROM PUBLISHER]

Abstract – Movements of adult Atlantic salmon were tracked through a series of four fish passes and an impoundment on the River Conon system, Northern Scotland. Proportions of fish passing individual obstructions ranged from 63 to 100%. The cumulative effect was that only 4 of the 54 tagged fish reached the spawning areas. The fish were delayed for 1–41 days at a pool-and-overfall ladder and 1–52 days at a Borland fish lift. The fish swam through a 10 km long reservoir at 0.21–1.16 km·h[sup -1] . A total of 13 fish negotiated a 2.5 km long, 3 m diameter diversion tunnel through a mountain to their home river. High levels of electromyogram (EMG) activity were recorded during ascent of a pool-and-overfall fish ladder, indicating that high energy demanding burst swimming was required. [ABSTRACT FROM AUTHOR]