Sediment preferences and size-specific distribution of young-of-the-year Pacific halibut in an Alaska nursery

A combination of laboratory experiments and field surveys was used to test the hypotheses that responses to sediments change with fish size and that sediment grain-size is the predominant environmental factor affecting small-scale distribution in young-of-the-year (yoy) Pacific halibut Hippoglossus stenolepis . Laboratory tests showed that the smallest fish (31–40 mm L _T) chose fine sediments (muddy and fine sands), fish 51–70 mm had high selectivity (primarily medium sand), and the largest fish (80–150 mm) were not selective although they avoided the largest grain-sizes (pebbles and granules). Sediment preferences were correlated with size-dependent burial capabilities. Beam trawl collections were made over a 6 year period in Kachemak Bay, Alaska, to examine the distribution of yoy Pacific halibut (14–120 mm L _T) using small size classes (e.g. 10 mm intervals). Canonical correlation analysis showed that the per cent of sand in the sediment was a highly significant variable for all but one size and date combination. Catch per unit of effort (CPUE) for newly settled fish (<30 mm L _T) was highest on very fine sand, fish 41–80 mm were most abundant on fine sand, and the largest yoy fish (81–120 mm) were abundant over a range of sediments from fine sand to mud. Except for the smallest fish, Pacific halibut in the field were associated with sediments somewhat finer than predicted from the laboratory experiments; however, virtually all were captured where they could bury easily. The ability of flatfish to bury and shelter in sediment is related to fish size; consequently, habitat associations shift rapidly during the first year of life. Habitat models for yoy flatfishes should consider size-dependent shifts in capabilities and preferences.     

Isolation and characterization of cDNA clones for RNA species induced by substituted benzenesulfonamides in corn

A search of compounds capable of inducing specific gene expression in plants without affecting growth and development led to the examination of changes in the pattern of gene expression in corn after treatment with substituted benzenesulfonamide herbicide safeners. Following hydroponic treatment of corn with the safener N-(aminocarbonyl)-2-chlorobenzenesulfonamide (2-CBSU), the specific induction of new translatable mRNA species was observed. Replicate copies of a cDNA library made using RNA from 2-CBSU-treated corn roots were differentially screened with cDNA probes made from either the same mRNA fraction used for library construction or mRNA isolated from roots treated with 2-chlorobenzenesulfonamide (2-CBSA), an inactive analog of the safener. Colonies showing hybridization only with the probe made using mRNA from 2-CBSU-treated roots were further characterized to assess the specificity of the induction and decay of the corresponding induced RNA species. RNA blot analyses showed two clones, designated In2-1 and In2-2, contained plasmids that hybridized to RNAs that were induced from an undetectable background in corn roots within 30 minutes after treatment with 2-CBSU. Leaf and meristem tissues showed similar inductions of the In2-1 and In2-2 RNA species after a delay of several hours. In addition, both RNA species were induced in corn by foliar application of 2-CBSU. In contrast, neither RNA species was induced following stress treatments of plants. These results indicate a substituted benzenesulfonamide safener might be used with the promoters from the In2-1 and In2-2 genes to develop a new inducible gene expression system for plants.     

Determination of the P/2e- stoichiometries at the individual coupling sites in mitochondrial oxidative phosphorylation. Evidence for maximum values of 1.0, 0.5, and 1.0 at sites 1, 2, and 3

P/2e- stoichiometries in six assay systems spanning different portions of the respiratory chain were estimated by direct determinations of Pi uptake in suspensions of bovine heart mitochondria containing a hexokinase trap. The electron donors were malate + pyruvate, succinate, and ascorbate + N,N,N',N'-tetramethyl-p-phenylenediamine, and the electron acceptors were ferricyanide (Site 1, Site 2, and Sites 1 + 2) and O2 (Sites 1 + 2 + 3, Sites 2 + 3, and Site 3). A major objective was to find conditions in which the six systems yield results in sufficiently good agreement to allow confidence as to their reliability. This objective was achieved, and maximum values of 1.1, 0.5, and 1.0 were observed in the Sites 1, 2, and 3 systems, respectively. This required that the energy-conserving reactions be relatively nonlimiting and that the P/2e- ratios be estimated from the slopes of plots of respiration rate versus phosphorylation rate obtained by inhibiting oxidative phosphorylation with respiratory chain inhibitors. The latter requirement allows avoidance of the effect of an apparent endogenous uncoupler and is based on the observation (Tsou, C. S., and Van Dam, K. (1969) Biochim. Biophys. Acta 172, 174-176) that uncoupling agents at low concentrations decrease the rate of phosphorylation nearly as much in absolute amount at low rates of respiration as at high rates. The maximum P/2e- stoichiometry at Site 1 is considered to be 1.0, and the value observed in the Site 1 system is suggested to be higher as a result of H+ ejection at the transhydrogenase level. Respiratory control due to carboxyatractyloside inhibition was examined and found to differ greatly among the systems. It is pointed out that this observation is not consistent with the lack of complete control being due primarily to ion cycling and that, in view of this, the relatively meager control at Site 3 is not consistent with O2 being reduced on the matrix side of the coupling membrane.     

Acute toxicity effects of ibuprofen on behaviour and haematological parameters of African catfish Clarias gariepinus (Burchell, 1822)

Indiscriminate discharge of pharmaceutical waste into the aquatic ecosystem may pose serious health challenges to aquatic biota. The effect of acute exposure to ibuprofen was evaluated using changes in behaviour and haematological parameters under static bio-assay method in Clarias gariepinus. Test specimens were exposed to acute concentrations of ibuprofen (0.28, 0.33, 0.38, 0.43 and 0.48 mg l^?1) for 24, 48, 72 and 96 h durations respectively. Behavioural and phenotypic changes were observed in surviving fish. There were significant (p < 0.05) concentration and duration-dependent increases in erythrocyte (RBC), haemoglobin (Hb), pack cell volume (PCV) and leukocytes (WBC) in treated fish compared to the control. Insignificant decreases (p > 0.05) in mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were observed in treated fish compared to the control. Ibuprofen elicited dose and duration- dependent decrease in neutrophil counts with the decreases being significant (p < 0.05) in the higher doses of 0.43 and 0.48 mg l^?1. Ibuprofen did not elicit any significant changes in monocytes, basophils and eosinophils. Changes observed in this study showed that ibuprofen negatively affected the health of the fish and we recommend that discharge of ibuprofen into the aquatic environment should be monitored and controlled.     

Hunger and light level alter response to bait by Pacific halibut: laboratory analysis of detection, location and attack

Laboratory experiments with Pacific halibut Hippoglossus stenolepis revealed that hunger level had a significant effect on the first detection of bait, the number of baits located and attacked, the time required to locate and attack baits and handling times. In all cases, feeding motivation and efficiency increased with hunger. Light level influenced general locomotory activity and location and attacks on baits, but not detection or handling times. The effect of light was interactive with fish hunger level. Hungry fish could locate and consume baits in all light levels, ranging from daylight conditions to near darkness (10⁻⁸ µmoles photons m⁻² s⁻¹), but location, attack and handling times were all significantly elevated in low light conditions, and attack rates were significantly reduced. In the dark, only 50% of the baits were located and only 17% were attacked. Performance metrics were relatively similar among three higher light treatments (10⁻⁵, 10⁻³ and 10⁻¹ µmoles photons m⁻² s⁻¹) where bait location and attack were more efficient. Active space and effective area associated with baited fishing gear will vary because hunger and light levels affect variation in bait detection, locomotion and feeding behaviour. Consequently, fishing activity and stock assessments that depend upon bait may be compromised by spatial and temporal variation in prey abundance, time of day, season, depth and other environmental variables that influence feeding motivation and efficiency.     

Changes in large herbivore populations across large areas of Tanzania

We collated aerial census data collected during the late 1980s to early 2000s for large herbivore populations in eight large census zones in Tanzania. Of the ungulate populations that showed significant changes in densities at the start versus end of this decade, most declined; very few populations increased significantly. Thomson's gazelle, Grant's gazelle, hartebeest, reedbuck, roan antelope, sable antelope, warthog and zebra, for example, declined in over 50% of the zones where they were surveyed. Interestingly, small‐bodied species fared particularly poorly in many census zones, whereas elephant and giraffe generally fared well across the country. Most populations of all herbivores declined in some portions of the country (e.g. Burigi‐Biharamulo, Katavi, Greater Ruaha and Tarangire census zones). These surveys suggest that, even in a country renowned for its protected areas and conservation commitment, some large herbivore populations need more conservation attention in order to remain stable.     

ADENINE NUCLEOTIDE-INDUCED CONTRACTION OF THE INNER MITOCHONDRIAL MEMBRANE : II. Effect of Bongkrekic Acid

In bovine heart mitochondria bongkrekic acid at concentrations as low as about 4 nmol/mg protein (a) completely inhibits phosphorylation of exogenous adenosine diphosphate (ADP) and dephosphorylation of exogenous adenosine triphosphate (ATP), (b) completely reverses atractyloside inhibition of inner membrane contraction induced by exogenous adenine nucleotides, and (c) decreases the amount of adenine nucleotide required to elicit maximal exogenous adenine nucleotide-induced inner membrane contraction to a level which appears to correspond closely with the concentration of contractile, exogenous adenine nucleotide binding sites Bongkrekic acid at concentrations greater than 4 nmol/mg protein induces inner membrane contraction which seems to depend on the presence of endogenous ADP and/or ATP. The findings appear to be consistent with the interpretations (a) that the inner mitochondrial membrane contains two types of contractile, adenine nucleotide binding sites, (b) that the two sites differ markedly with regard to adenine nucleotide affinity, (c) that the high affinity site is identical with the adenine nucleotide exchange carrier, (d) that the low affinity site is accessible exclusively to endogenous adenine nucleotides and is largely unoccupied in the absence of bongkrekic acid, and (e) that bongkrekic acid increases the affinity of both sites in proportion to the amount of the antibiotic bound to the inner membrane.