Community structure and feeding ecology of mesopelagic fishes in the slope waters of King-George Island (South Shetland Islands, Antarctica)

The role of mesopelagic fishes in the Southern Ocean ecosystem and more particular their trophic effect on the standing stock of mesozooplankton is at present poorly understood. To get a deeper insight in the Antarctic mid-water ecosystem the mesopelagic fish community of the King George Island slope (South Shetland Islands) was sampled with a pelagic trawl in 1996. The community structure was analysed and the feeding ecology was studied of the five most abundant species. A total of 18 mesopelagic fish species in 10 families was identified. Of these, the Myctophidae was the most important family by species number (9 species), individual number (98.5% of all individuals)and fish wet weight (87.3% of the total weight). The assemblage was numerically dominated by four myctophids (Electrona antarctica, Gymnoscopelus braueri, Gymnoscopelus nicholsi,Protomyctophum bolini) and one gempilyd (Paradiplospinus gracilis). Multivariate statisticalanalysis of the mesopelagic fish data reveals two major groups of stations according to the sampleddepth: a shallow group of stations (295â450 m depth) and a deeper group of stations (440â825 mdepth). The change in relative abundance of mesopelagic fish species at 440â450 m coincides withthe presence of warmer and denser Circumpolar Deep Water at and below these depths. Deeperstations were characterized by a higher density and increased diversity of mesopelagic fish species.The community patterns identified correlated well with the vertical depth distribution of the mostabundant species. Dietary analysis reveals that myctophids are mostly zooplanktivorous, while thegempilyd P. gracilis is classified as a piscivorous predator. The small P. bolini feed mainly oncopepods of the species Metridia gerlachei, while the most important prey item of the largermyctophids E. antarctica, G. braueri, and G. nicholsi were various species of euphausiids.Investigation of feeding chronology showed that G. nicholsi and P. bolini were feeding day andnight. Daily ration estimates for myctophid species ranged from 0.28% to 3.3% of dry body weight(0.5â5.94% of wet body weight). Krill (Euphausia superba) were the most important food of E.antarctica and G. nicholsi, accounting for 53.1% and 58.3% of the total food weight, respectively.The annual removal from the krill stock by both species was estimated to amount to 11.1â26.7% inthe South Shetland Islands region. This estimate emphasizes the important role of mesopelagic fish inthe Antarctic ecosystem as a prevalent consumer of krill

Feeding Ecology of early stages of mesopelagic fishes in the Equatorial and tropical Atlantic

We analysed the trophic ecology of the early ontogenetic stages of six mesopelagic fish species (Bathylagoides argyrogaster, Argyropelecus sladeni, Sternoptyx diaphana, Diaphus vanhoeffeni, Hygophum macrochir, and Myctophum affine), which have different morphologies, vertical distributions, and taxonomic affiliations. The larvae and transforming stages of the sternoptychids fed both during the day and at night. However, larvae of the other species fed during the day, as they apparently rely on light for prey capture. The transforming stages of myctophids showed a similar daylight feeding pattern to their larvae, but in D. vanhoeffeni both day and night feeding was evident, thereby indicating the progressive change toward the adult nocturnal feeding pattern. The number of prey and their maximum sizes were linked to predator gut morphology and gape size. Although the maximum prey size increased with predator development, postflexion larvae and transforming stages also preyed on small items, so that the trophic niche breath did not show evidence of specialization. In all the species, copepods dominated the larval diet, but the transforming stages were characterized by increasing diet diversity. Despite the poor development of these early stages, Chesson’s selectivity index calculated for larvae and transforming stages showed positive selection for particular prey

Trophic position of lanternfishes (Pisces: Myctophidae) of the tropical and equatorial Atlantic estimated using stable isotopes.

Lanternfishes (Myctophidae) constitute the most important component of the daily vertically migrating mesopelagic fish community. This research addresses the estimation of the trophic position and diet of myctophids using stable isotope analyses. Fishes were collected across the central Atlantic, from a very productive zone influenced by the Mauritanian upwelling to the western oligotrophic equatorial waters. The survey also encompassed a zone of low oxygen concentration in the mesopelagic layers. Determinations of d13C and d15N values were made on the 20 most frequent and abundant myctophids, from small-sized species (e.g. Notolychnus valdivae) to larger ones (e.g. Myctophum punctatum). Isotope analyses on the seston and several plankton groups were also performed to assess the influence of zonal differences in trophic position (TP) calculations, and to use as food sources in diet estimations. Myctophids displayed a narrow range of trophic positions, being greater than 2 and less than 4, except for N. valdiviae (TP ¼ 1.7). Comparisons of diets estimated through an isotopic mixing model differentiated the smallest species, with a strong seston signature (Diogenichthys atlanticus and N. valdiviae), from the Diaphus species of medium sizes, (D. brachycephalus, D. holti, and D. rafinesquii), which feed on prey of higher TP values

A gene expression study of normal and damaged cartilage in anteromedial gonarthrosis, a phenotype of osteoarthritis

Objective: To identify osteoarthritis (OA) relevant genes and pathways in damaged and undamaged cartilage isolated from the knees of patients with anteromedial gonarthrosis (AMG) - a specific form of knee OA. Design: Cartilage was obtained from nine patients undergoing unicompartmental knee replacement (UKR) for AMG. AMG provides a spatial representation of OA progression; showing a reproducible and histologically validated pattern of cartilage destruction such that damaged and undamaged cartilage from within the same knee can be consistently isolated and examined. Gene expression was analysed by microarray and validated using real-time PCR. Results: Damaged and undamaged cartilage showed distinct gene expression profiles. 754 genes showed significant up- or down-regulation (non-False discovery rate (FDR)