Otolith and somatic growth rates in Atlantic salmon parr, Salmo salar L: evidence against coupling

It is often assumed that otolith growth is in some way dependent on somatic growth (i.e. that the two processes are coupled). We examined the relationships between sagitta radius and fork length in 0+ Atlantic salmon parr that would subsequently smolt aged 1 + (UMG fish) or 2+ (LMG fish). Repeated measurements of fork lengths of individually marked parr, taken over a 211-day period from first feeding, were compared to sagitta radii on the same measuring dates (obtained by analysis of daily increments). The results showed that there was a linear relationship between fork length and otolith radius in UMG parr. However, this was not true for LMG parr. These fish enter a state of natural anorexia in their first autumn (despite excess food), but their otoliths continued to grow at the same rate despite the virtual cessation of somatic growth; they had therefore developed disproportionately large otoliths by the end of the study period. The relative growth rates of soma and otoliths first changed in LMG fish in late July/early August; this is the most precise estimate yet obtained of the timing of divergence in the developmental pathways of UMG and LMG parr. The rate of sagitta accretion was consistently lower in LMG parr, possibly indicating a lower metabolic rate in these fish. The results are discussed in relation to previous theories of the relationship between otolith and somatic growth.     

Cleanability in relation to bacterial retention on unused and abraded domestic sink materials

The relative cleanability of stainless steel, enamelled steel, mineral resin and polycarbonate domestic sink materials was assessed by comparing the number of organisms remaining on surfaces after cleaning. In unused condition all materials, other than one enamelled steel, were equally cleanable. Stainless steel, abraded artificially or impact damaged to a similar degree as stainless steel subjected to domestic wear, retained approximately one log order less bacteria after cleaning than the other materials subjected to the same treatments. Little difference in cleanability was recorded between the abraded surfaces of the other materials although enamelled steel surfaces were less cleanable than mineral resin or polycarbonate after impact damage, because of the greater susceptibility of enamelled steel to damage by this treatment. When cleaning time was extended beyond 10 s for the abraded and impact damaged materials, their cleanability was not enhanced as compared with stainless steel. Changes in surface finish after abrasion were assessed by surface roughness measurement and scanning electron microscopy. Surfaces with poor cleanability before and after abrasion were characterized by pitting, crevices or jags. These surfaces are likely to retain more bacteria because of increased numbers of attachment sites, a larger bacterial/material surface contact area and topographical areas in which applied cleaning shear forces are reduced. Materials that resist surface changes, e.g. stainless steel, will remain more hygienic when subjected to natural wear than materials which become more readily damaged.     

Feeding motivation and response to predation risk in Atlantic salmon parr adopting different life history strategies

Feeding intensity was measured before (baseline level) and after (disturbed level) brief exposure to a potential predator in groups of 0+ Atlantic salmon, Salmo salar. parr destined to follow either a fast-growth, early-smolting life history (upper modal group or UMG fish) or a slow-growth, late-smolting life history (lower modal group or LMG fish). Feeding intensity decreased following exposure to the predator. While the absolute decrease in feeding intensity is constant regardless of baseline level, the proportionate decrease is negatively related to pre-presentation feeding intensity. Parr that are strongly motivated to feed thus maintain a higher food intake and incur greater risks when foraging in the presence of a predator. No differences in baseline or disturbed feeding intensity of UMG and LMG parr were found up to September of their first year. Previous work has shown that baseline feeding intensities decrease in LMG fish after September but increase in UMG fish. In the present study, these differences were reflected in greater disturbed feeding intensities in UMG fish, but fish destined to follow different life history patterns do not differ in risk-taking, once these differences in baseline feeding motivation have been taken into account.     

Physiological effects of Na2SO4 and NaCl on callus cultures of Brassica campestris (Chinese cabbage)

Hypocotyl-derived callus cultures of Brassica campestris L. ssp. pekinensis cv. Kim-jung (Chinese cabbage) were grown on Murashige and Skoog medium containing no additional salt, NaCl or Na₂SO₄. Na₂SO₄ was more than twice as inhibitory in comparison to the same concentration of NaCl when growth and fresh:dry weight ratios of established callus were measured. Levels of protein, starch, sucrose and α-amino nitrogen were not significantly altered in salt-grown callus. Concentrations of reducing sugars and chlorophyll were 2–3 times greater in callus grown on either salt. Proline concentration increased 15–20 fold on the highest levels of salt. Final concentrations (reached in 20–24 days) were closely correlated to the initial Na⁺ concentration of the medium, regardless of salt type. The osmotic potential in callus transferred to NaCl or Na₂SO₄ reached a maximum negative value after 16 days. For both salts, subsequent increases were correlated to increases in fresh:dry weight and growth. On both salts, turgor remained relatively constant (0. 6–0.75 MPa). Changes in Na⁺, K⁺, Mg²⁺ and Ca²⁺ content were correlated to initial Na⁺ concentration in the medium, not salt type. Accumulation of Na⁺ was accompanied by loss of K⁺ and Mg²⁺. Six to seven times less sulfate was measured in callus grown on Na₂SO₄ than chloride in callus grown on similar concentrations of NaCl.     

Nucleotide sequence of diatom plasmids: identification of open reading frames with similarity to site-specific recombinases

We have determined the nucleotide sequence of two small circular DNA plasmids, pCf1 and pCf2 [22], from the marine diatom Cylindrotheca fusiformis. pCf1 is 4273 bp, and pCf2 is 4079 bp in size. In each plasmid, all of the major open reading frames (ORFs) are encoded on the same DNA strand. Two ORFs are similar, comparing the two plasmids. ORF218 (pCf1) and ORF217 (pCf2) share 80% amino acid identity and ORF482 (pCf1) and ORF484 (pCf2) share 54% amino acid identity. ORF218/217 shows significant similarity (28–31% amino acid identity) to the Tn3 class of resolvases. Resolvases are most commonly found in bacterial transposons. However, two other features found in the Tn3 class of transposon are missing in the plasmids; an ORF encoding a transposase and terminal inverted repeat sequences. This, and data mapping the portions of the plasmids that hybridize to genomic chloroplast DNA, suggest that the plasmids do not contain active transposons. By analogy with the R46 plasmid from Enterobacter [5, 6], another potential role for the resolvases encoded by pCf1 and pCf2 is the conversion of multimeric forms of the plasmid to monomers. The similarity of ORF218/217 to resolvases documents the first identification of a potential coding function in an algal plasmid.     

Reactivity of medium-chain acyl-CoA dehydrogenase toward molecular oxygen

The free two-electron-reduced form of medium-chain acyl-CoA dehydrogenase is reoxidized by 120 microM molecular oxygen (50 mM phosphate buffer, pH 7.6, 2 degrees C) with a half-time of approximately 7 s. Reoxidation yields hydrogen peroxide as a major product with only traces of the superoxide anion. In contrast, enzyme reduced with octanoyl-CoA is extremely slowly reoxidized oxygen, and so a series of 14 different substrate analogues have been tested to assess the structural factors responsible for this effect. Complexes with redox-inactive ligands such as 3-thia- and 2-azaoctanoyl-CoA lead to an approximately 3000-fold slowing of the rate of reoxidation of the free dihydroflavin form of the enzyme. Comparable ligands lacking the thioester carbonyl function are much less effective with rates some 1.3-4-fold slower than the free enzyme. The strong suppression of oxygen reactivity observed with certain ligands is probably not simply a steric effect but may reflect desolvation of the active site and consequent destabilization of the superoxide anion intermediate formed during reoxidation of the flavin. The profound differences in oxygen reactivity between acyl-CoA dehydrogenase and acyl-CoA oxidase and the unusual stability of certain flavoprotein semiquinones in air are discussed in terms of these thermodynamic and kinetic arguments.     

Behavioural responses of benthic and pelagic Arctic charr to substratum heterogeneity

Responses to environmental heterogeneity were studied in laboratory-reared offspring of two morphs of Arctic charr Salvelinus alpinus from Loch Rannoch, Scotland, one occupying the pelagic zone and feeding predominantly on zooplankton and the other being benthic in habit and feeding mainly on macroinvertebrates. When housed in groups in tanks with a black-and white striped base, benthic charr demonstrated a clear preference for dark areas, whereas pelagic fish positioned themselves at random with respect to substratum colour. In general, pelagic charr were much less aggressive than benthic charr. In pelagic fish, neither spacing nor aggression was affected by the visual heterogeneity of the substrate. In contrast, benthic charr swam closer together and fought more when housed over a uniform as opposed to a non-uniform substratum. The results are discussed in the context of habitat-specific visual requirements and of an interaction between visual complexity and territoriality previously described for Atlantic salmon Salmo salar .     

Effect of seasonal placement ofCotesia melanoscela (Hym.: Braconidae) on its potential for effective augmentative release againstLymantria dispar (Lep.: Lymantriidae)

Cohorts ofCotesia melanoscela (Ratzeburg) (Hymenoptera: Braconidae) cocoons were exposed in the field at three Maryland locations to attack by natural enemies for two week periods, then were held in an outdoor insectary untilC. melanoscela adult or hyperparasitoid emergence. The timing of placement of theC. melanoscela cocoons in the field had a profound effect on the number ofC. melanoscela that survived and emerged as adults in synchrony with the field occurence of susceptible early-instarLymantria dispar (L.) larvae. The proportion of emerged adults available during susceptible host stages ranged from 1–92%, depending on dates of release. November or December placements ofC. melanoscela cocoons were most effective with 74–92 % emergence of adults during peak periods of susceptible host stages. Spring placements were least effective. The causes of ineffective placement, which varied with location and with date, were program (handling) loss, non-emergence, attack by hyperparasitoids, predation, andC. melanoscela adult emergence at times when appropriateL. dispar life stages would not be present. We concluded that November/December releases avoided natural enemies and promoted appropriate diapause and post-diapause development that enhanced survival and synchrony of adult emergence with host stage susceptibility.     

Influence of different luminols on the characteristics of the chemiluminescence reaction in human neutrophils

In search for a luminol with very high output of light, 20 different luminol samples were tested for their ability to enhance the chemiluminescence reaction in phorbol myristate acetate activated human neutrophils. We found that the majority of luminols tested (17 samples) gave almost the same light output from neutrophils, and that the major part of the activity was from an intracellular origin. Owing to the fact that three isoluminol samples were unable to monitor respiratory burst activity taking place intracellularly, a very low level of chemiluminescence was obtained with these samples. Their light output was, however, greatly increased when horseradish peroxidase or myeloperoxidase was added, showing that the light-generating reaction with isoluminol as well as with luminol is peroxidase-dependent. The fact that isoluminol could also use myeloperoxidase as amplifying peroxidase, suggests that the lack of measurable intracellular activity in the presence of isoluminol is somehow related to a limited or restricted diffusion of the molecule to intracellular sites. The isoluminol system constitutes a sensitive system for measuring release of oxygen metabolites from phagocytic cells.     

Daily feeding rhythms in Atlantic salmon II: size-related variation in feeding patterns of post-smolts under constant environmental conditions

Previous studies of feeding rhythms in post-smolt Atlantic salmon Salmo salar have produced variable results. Therefore, the present study was performed to clarify the source of these differences and to examine size-related variation in daily feeding patterns. A small group of hatchery reared post-smolts was kept in an indoor seawater tank under conditions of constant photoperiod and light intensity, and negligible diurnal variation in water temperature. Feeding responses were monitored by video camera throughout the day. The resultant feeding pattern for the population mirrored an earlier study, with the highest levels of feeding activity in the early morning and late evening. Differences between this and other studies may be due to variation in climate, season or life-history stage. Daily feeding patterns were size-dependent. The largest fish fed at a relatively constant level through the day, medium-sized fish fed in a pattern similar to that described above for the population and small fish fed most at first and last light. These differences were due probably to the effect of competitive interactions upon fish of different sizes.