Assimilation of dietary free amino acids,peptides and protein in post-larval Atlantic halibut (<Emphasis Type="Italic">Hippoglossus</Emphasis><Emphasis Type="Italic">hippoglossus</Emphasis>)

With the aim of improving the formulation of diets for early stages of marine fish, post-larval Hippoglossus hippoglossus (56 days after first feeding; 23 mg dry weight) were tube-fed liquid diets of radiolabelled L-(¹⁴C) free amino acids (FAA diet), peptides (PEPT diet) and protein (PROT diet), in order to compare the kinetics of transfer from gut into the liver and carcass. The test diets were prepared using equal concentrations of amino acids (AA) and fed as a single pulse (0.3 µl, 2.2 µg AA). The PROT diet consisted of methylated-¹⁴C-labelled (mainly lysine) bovine serum albumin (BSA), the PEPT diet was the PROT diet digested with trypsin and the FAA diet consisted of an amino acid mixture based on BSA composition with added ¹⁴C-lysine. The common labelling with ¹⁴C-lysine permitted a comparison of the three diets. Based on dissection and distribution of the tracer in each compartment, the FAA diet was almost completely absorbed 1 h after the tube-feeding; PEPT and PROT diets required more time before they were processed by the digestive tract. The FAA diet was absorbed about eight times as fast as protein and about six times as fast as peptides from the gut. A low retention of label in the liver for all diets at all sampling times suggests that the liver does not store the AA at these absorption rates. The FAA diet had a higher assimilation efficiency (about 90%) than the PEPT diet (about 12%) and PROT diet (about 32%). FAAs, thus, appear to be superior to protein and peptides as a dietary source of amino acids in post-larval Atlantic halibut.     

Effect of deuterium-depleted water on reproduction of rainbow trout

During the artificial reproduction of salmonides, the fecundity can be increased either by improving the viability of spermatozoa, or by extending the time period during which a roe micropile remains open, thus allowing its fecundation. Practically, this can be achieved by the use of some fertilising techniques suitable for fish species. Here, we show that the reproduction of rainbow trout in a 1:1 solution of deuterium-depleted water and distilled water led to a significant increase in survival of roes during their embryonic development. Moreover, the addition of glucose and fructose into the deuterium-depleted fertilising solutions led to a further increase in roe survival during embryonic development. The increase in survival is mainly explained by an increase in the motility of spermatozoa.     

To what extent does upright sessile epifauna affect benthic biodiversity and community composition?

Small-scale habitat complexity, including that caused by biological structures, is an important factor in structuring benthic communities and also sometimes in increasing biodiversity. The aim of this study was to determine if hydroid colonies have an effect on the composition of benthic communities in the Irish Sea, and if so, which components of the fauna are affected. Forty-six seabed core samples were taken by divers from two sites off Port Erin, Isle of Man, Irish Sea. Half of these were centred on hydroid colonies, half were not. All taxa retained by a 63-m sieve from the cores were identified and counted. Community composition and diversity were compared between hydroid and non-hydroid cores using multivariate and univariate methods. Benthic communities were significantly different between the two sample groups. This was almost entirely due to the presence of sessile and mobile epifaunal taxa in the hydroid cores. The tube-building amphipod, Ericthonius punctatus, was particularly abundant attached to the hydroid stems. Infauna was not significantly different between the two groups. Upright sessile epifauna may play a particularly important role in the Irish Sea as a settlement substrate for juvenile scallops (Pecten maximus and Aequipecten opercularis), which are an important fishery resource in this area. The 11-year closure of an area to dredging has not only enhanced scallop stocks but has had the added benefit of enhancing habitat complexity and biodiversity.Communicated by J.P. Thorpe, Port Erin     

The highly specialised gut of Fritillariidae (Appendicularia: Tunicata)

The morphology and some functions of the gut of Fritillaria pellucida and Fritillaria formica (Fritillaridae) were investigated by light and electron microscopy, and also by means of histochemical and immunohistochemical techniques. Fritillarids, very important for their abundance and ecological impact in marine ecosystems, have a very simplified gut: a straight oesophagus connects the pharynx to the digestive nucleus, composed of globular stomach and rectum, connected dorsally through a very short proximal intestine. The latter is characterised by a few (two to four) extremely specialised cells, completely filled with mitochondria associated tightly with membrane infoldings showing strong ATP-ase activity, and probably involved in the osmoregulation of internal body fluids. The gut is formed of an extremely low number of cells, which, although poorly diversified, are very large in the stomach and rectum. Food transfer along the gut depends on and is regulated by well-developed cardiac and pyloric valves, and signs of general digestive and absorptive activity are recognisable all along the brush border of the main tracts. The macroscopic organisation and cytological characters of the gut in fritillarids are completely different from those of the oikopleurids. In particular, fritillarids lack specialised cells for endocytosis and intracellular digestion, like those described in the genus Oikopleura. The general simplification and specialisation observed in Fritillaria gut may account for their elevated growth rate and abundant diffusion in all oceans.     

Changes in otolith microstructure and microchemistry during larval development of the European conger eel (<Emphasis Type="Italic">Conger conger</Emphasis>)

Otolith microstructure and chemical composition (Sr:Ca ratios) of the European conger eel (Conger conger) were examined during the larval developmental stages by scanning electron microscopy and wavelength dispersive spectrometer. Back-calculated hatching dates from the otolith microstructure of the developing leptocephali indicate a protracted spawning season from December to June. The early age of our developing specimens captured south of the Azores Islands suggests that the conger eel has another spawning area closer to Azores than the Mediterranean. Otolith increment width, which was relatively constant and narrow in the developing leptocephalus stage, increased sharply at age 170-250 days. Sr:Ca ratios in the otolith, which increased during the developing leptocephalus stage, showed a rapid drop coinciding with the increase in increment width. These coincidental changes were regarded as the onset of metamorphosis for this species. A close linear relationship between the age at metamorphosis and otolith growth rate indicates that the faster-growing larvae metamorphose earlier, suggesting that somatic growth should play an important role in the timing of metamorphosis. As shown in earlier work, the existence of an otolith marginal zone with unclear rings during metamorphosis prevents an accurate estimate of the larval stage duration of this species.     

Sorption of the natural endocrine disruptors,oestrone and 17 beta-oestradiol in the aquatic environment

Adsorption of hydrophobic contaminants at the particle/water interface is one of the key processes controlling their fate in the aquatic environment. The sorption of the natural female hormones oestrone and 17-oestradiol has been studied under simulated riverine conditions. Both the kinetics and the effects of varying fundamental environmental parameters (e.g. sediment properties) on the thermodynamic equilibrium partition coefficient (K _p) have been studied in continuous and batch sorption experiments, respectively. Results showed that the sorption of oestrone and 17-oestradiol by sediment was relatively slow, reaching equilibrium in 50 days. In addition, relatively small adsorption of both oestrone and 17-oestradiol onto the sediment was observed, with K _p values between 200 and 250 mL g^–1. The comparable K _p values of the two compounds reflect their structural similarity. It can be concluded that the two endocrine disruptors, oestrone and 17-oestradiol remain primarily in association with the aqueous phase.     

Transport of Pollutant in Open Channel with Short Waves

This study examines the effect of short period water waves on the longitudinal mixing of pollutants in open channel flow. These waves create orbital motions and therefore increase the magnitude of the dispersion coefficient. Experiments are conducted for non-wavy and wavy flow. The values of the longitudinal dispersion coefficients are determined by applying the method of least squares to the measured solute concentrations at various time intervals. For non-wavy flow, the measured values of longitudinal dispersion coefficient match closely with those computed from the empirical equation given by Seo [1]. For wavy flow, a new factor called the wave parameter (a/TU _*, a=wave amplitude, T=wave period, U _*=shear velocity) is found important and a nonlinear multiple regression analysis is used to derive a new expression for the wave induced longitudinal dispersion coefficient (WILDC). An uncertainty analysis is conducted as per IS Code 5168 and the confidence interval is determined. Linear water wave theory is applied to modify the existing expression of the longitudinal dispersion coefficient of Seo [1] by including the effect of short waves. A mathematical model for WILDC is then developed. Comparative study between wavy and non-wavy flow cases has been conducted. The results clearly show an increase in the magnitude of longitudinal dispersion coefficient in the presence of waves.     

Latitudinal and bathymetric trends in body size of the deep-sea gastropod<Emphasis Type="Italic"> Troschelia berniciensis</Emphasis> (King)

Body size is a fundamental topic in ecology with important implications for community structure and biodiversity. Although there are numerous studies addressing patterns of geographic variation of body size in deep-sea benthos, results are conflicting. Thus geographic patterns of body size in deep-sea organisms remain poorly described. We analysed depth and latitudinal trends of body size in a species of gastropod, Troschelia berniciensis (King, 1846) from the eastern North Atlantic. We tested the hypotheses that (1) body size increases linearly with latitude and (2) body size increases with depth. Results partially supported the predictions. Firstly, there was a significant linear increase of body size with latitude, but this trend was weak. Secondly, body size decreased with depth. Environmental gradients that cause large-scale patterns of body-size variation in surface environments would have little effect on communities living at great depths. Latitudinal and depth clines may be produced by independent mechanisms that operate on different scales of time and space.Communicated by J.P. Thorpe, Port Erin     

Genetic structure of the scleractinian coral<Emphasis Type="Italic"> Platygyra sinensis</Emphasis> in Hong Kong

Genetic structure was studied in Platygyra sinensis from six sites in Hong Kong by allozyme electrophoresis using an isoelectric focusing gel (IEF). Seven variable loci were detected using six enzyme systems. The number of alleles per locus ranged from 3.3 to 3.6 in the six samples, and heterozygosity from 0.429 to 0.540. Genotype frequencies were generally close to Hardy–Weinberg expectations. The values of unique multilocus genotype to the number of individuals for each sample (N_G/N) and observed genotypic diversity to expected genotypic diversity (G_O/G_E) were high, indicating a high level of sexual reproduction. Variation in allele frequencies among sites was low (F_ST=0.017), as was Nei's unbiased genetic distance (D), suggesting genetic similarity among sites.Communicated by T. Ikeda, Hakodate     

Feeding strategies and diets of breeding grey-headed and wandering albatrosses at South Georgia

The foraging areas and diets of the grey-headed albatross Thalassarche chrysostoma and wandering albatross Diomedea exulans were studied in March/April 2000 at Bird Island, South Georgia, during their respective chick-rearing and brood-guard periods. Oceanographically, March/April 2000 was abnormal, with warm conditions close to South Georgia. These conditions affected albatross foraging behaviour, particularly that of grey-headed albatrosses. Both species tended to forage in different areas of the ocean, with significant differences in trip durations. Grey-headed albatrosses (n=9) foraged mainly in Antarctic waters (predominantly shelf waters of the South Shetland Islands and Antarctic Peninsula, and also in oceanic waters around South Georgia), feeding mainly on krill (Euphausia superba; 77% by mass). Foraging trips lasted 13.3 days (range: 5–26 days), far longer than the 1–3 days found in previous studies. Only one grey-headed albatross was associated with the APF (Antarctic Polar Front), a reported foraging area in recent studies. Wandering albatrosses (n=9) foraged in Antarctic (South Georgia Shelf) and Antarctic Polar Frontal Zone (APFZ) waters, with trips of 1–4 days trip duration (usual for this species), feeding on fish (46% by mass) and cephalopods (32%). One bird was associated with the APF, and two birds foraged on the shelf/shelf break over the Patagonian shelf. These findings suggest that sea surface temperature anomalies, produced by movement of the APF closer to South Georgia or by eddies, may have had an effect on the foraging strategy of grey-headed albatrosses that year (the main prey of grey-headed albatrosses in previous studies, the ommastrephid Martialia hyadesi, is known to be associated with the APF). Also, when both albatross breeding periods overlap, their foraging areas were complementary, which reflected the prey taken.