Effects of dietary vitamin D3 administration on innate immune parameters of seabream (Sparus aurata L.)

The present study assesses the in vivo effect of vitamin D₃ or cholecalciferol on some innate immune parameters of the gilthead seabream (Sparus aurata L.). Cholecalciferol was orally administered to seabream specimens in a commercial pellet food supplemented with 0 (control); 3750; 18,750 or 37,500 U kg^?1 and fish were sampled after 1, 2 and 4 weeks of treatment. Serum and head– kidney leucocytes were obtained and humoral (peroxidase and complement activity) and cellular (leucocyte peroxidase content, phagocytic, respiratory burst and natural cytotoxic activities) innate immune parameters were measured. Diet supplementation with 37,500 U kg^?1 cholecalciferol for 2 or 4 weeks resulted in a significant increase in phagocytic ability or serum peroxidase content, respectively, whereas the 3750 and 18,750 U kg^?1 supplemented diets led to significant increases in the phagocytic capacity of leucocytes at week 2 compared with the values found in control fish. Natural cytotoxic activity was increased in leucocytes from fish fed for 1 week with 3750 U kg^?1 cholecalciferol. No significant differences were observed in complement activity or in respiratory burst activity in the assayed conditions. These results suggested that dietary vitamin D₃ administration has an effect on the innate immune parameters of gilthead seabream. The immunostimulant effect was greater on the cellular innate immune parameters assayed, suggesting that similar receptors to those present in mammals are involved in the action of this vitamin in the fish immune system.     

A comparative assessment of support vector regression,artificial neural networks,and random forests for predicting and mapping soil organic carbon stocks across an Afromontane landscape

Soil organic carbon (SOC) is a key indicator of ecosystem health, with a great potential to affect climate change. This study aimed to develop, evaluate, and compare the performance of support vector regression (SVR), artificial neural network (ANN), and random forest (RF) models in predicting and mapping SOC stocks in the Eastern Mau Forest Reserve, Kenya. Auxiliary data, including soil sampling, climatic, topographic, and remotely-sensed data were used for model calibration. The calibrated models were applied to create prediction maps of SOC stocks that were validated using independent testing data. The results showed that the models overestimated SOC stocks. Random forest model with a mean error (ME) of −6.5 Mg C ha⁻¹ had the highest tendency for overestimation, while SVR model with an ME of −4.4 Mg C ha⁻¹ had the lowest tendency. Support vector regression model also had the lowest root mean squared error (RMSE) and the highest R² values (14.9 Mg C ha⁻¹ and 0.6, respectively); hence, it was the best method to predict SOC stocks. Artificial neural network predictions followed closely with RMSE, ME, and R² values of 15.5, −4.7, and 0.6, respectively. The three prediction maps broadly depicted similar spatial patterns of SOC stocks, with an increasing gradient of SOC stocks from east to west. The highest stocks were on the forest-dominated western and north-western parts, while the lowest stocks were on the cropland-dominated eastern part. The most important variable for explaining the observed spatial patterns of SOC stocks was total nitrogen concentration. Based on the close performance of SVR and ANN models, we proposed that both models should be calibrated, and then the best result applied for spatial prediction of target soil properties in other contexts.     

Evaluation of different commercial feeds on grow-out silver black porgy,Sparidentex hasta (Valenciennes), for optimum growth performance,fillet quality,and cost of production

The objective of the study was to find a cost-effective feed from three commercial feeds, namely, Arasco (Saudi Arabia), Skretting (Turkey), and Biomar (Greece) for commercially producing silver black porgy (sobaity bream), Sparidentex hasta in Kuwait. For confidentiality, these feeds were randomly given code names, diets 1, 2, and 3, which were known only to the investigating staffs. The trash fish (diet 4) was used as the control. The experiment was conducted for 28 wk with grow-out sobaity bream (210.0 ± 0.51 g) using a flow-through system consisting of twelve 1-m³ tanks. There were three replicates for each treatment. Fish were fed two times daily at satiation level. The results showed that fish fed diet 2 resulted in significantly (P > 0.05) better growth performance, feed utilization, and higher fillet eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content compared to other diets. A comparison of fillet quality of cultured and wild sobaity bream showed no significant (P > 0.05) difference between sensory attributes, except that of ‘flavor’ in cooked fillets of wild sobaity bream. A simple economic analysis showed that the cost per kilogram of fish production was significantly (P > 0.05) the lowest in diet 2 (USD4.13), followed by diet 1 (USD5.70), diet 4 (USD6.33), and diet 3 (USD6.92). Thus, based on growth performance, feed utilization, cost of production, and nutritional quality of fillet, it is concluded that diet 2 may be recommended for commercial culture of sobaity bream in Kuwait. However, future research should focus on how to improve fillet quality of the cultured fish at par with wild fish by manipulating the feed formulation.     

Development and application of an ecological classification tool for fish in lakes in Ireland

A classification tool suitable for establishing the ecological status of lakes based on fish population parameters has been developed for the Republic of Ireland and Northern Ireland (EU Water Framework Directive Ecoregion 17). A lake typology relevant to fish populations in lakes from Ecoregion 17 was produced as part of the ecological classification tool development. Four lake types were determined based on fish metrics and abiotic variables from 43 “reference” lakes. The specific lake fish typology categorised lakes into low (≤67 CaCO₃ mg L⁻¹) or high (>67 CaCO₃ mg L⁻¹) alkalinity, and shallow (≤17 m) or deep (>17 m) maximum depth. The fish in lakes classification tool (FIL2) follows a novel multimetric predictive approach, assigning ecological status to a lake using two independent methods. FIL2 qualitatively defines a lake's ecological status based on fish metrics using discriminant classification rules and, using a generalised linear model, quantitatively derives an Ecological Quality Ratio (EQR, 0 < EQR < 1), along with associated confidence intervals. It is recommended that both methods are used to validate output and cross-check and highlight potential misclassification.     

Distribution characteristics and factors influencing the ecosystem in western Hubei

Western Hubei is the most concentrated area of forest resources in Hubei Province, and the knowledge of the distribution characteristics of ecosystem carbon density is important to understand the regional characteristics of carbon density and its mechanism of formation. Carbon density and factors influencing different layers in the ecosystem were studied by using field data. The average carbon density of ecosystems in western Hubei was 159.05 t/hm²; the carbon density of different forest types in descending order was Abies fargesii forests (362.25 t/hm²), mixed broadleaf-conifer forests (154.13 t/hm²), broad-leaved forests (146.09 t/hm²), and coniferous forests (135.76 t/hm²), and ecosystem carbon density increased with increasing age. The carbon density of the arborous layer, shrub layer, and soil layer of A. fargesii forests was significant higher than that of the other forests (P < 0.05), indicating the carbon storage per unit area of A. fargesii forests, which grow at higher elevations, was the greatest. The carbon density in arborous layers of broad-leaved forests, mixed broadleaf-conifer forests, and coniferous forests was 39.29 t/hm², 48.99 t/hm², and 48.39 t/hm², respectively. Those of the soil layer were 102.96 t/hm², 100.97 t/hm², and 82.37 t/hm², respectively, and there were no significant differences among them. Among the three forest types, carbon density in the litter layer was greater than that of the shrub layer, which indicated the litter layer plays an important role in carbon storage. The carbon density of mixed broadleaf-conifer forests was greatest, excluding A. fargesii forests, in medium (58.71 t/hm²) and mature forests (79.66 t/hm²). Thus, the carbon sink of mixed broadleaf-conifer forests had more potential than the others at the medium and mature forest stage. The soil layer carbon density in different forests constituted 60.67—70.48% of the entire ecosystem, and was 1.70—2.62 times greater than that of the arborous layer. There are many factors influencing ecosystem carbon density, which result from the interaction of environmental and topographical factors. The main explanatory variables of carbon density of the region were altitude, precipitation, and canopy density. The vegetation and soil layer carbon density increased as altitude increased, and the rate of change for every vertical 100 m was 1.3 t/hm² and 1.9 t/hm², respectively (P < 0.05). Although the annual average precipitation only affected the carbon density of the vegetation, it increased to 4 t/hm² (P < 0.01) when average precipitation was >100 mm.     

Texture analysis in liver of common carp (Cyprinus carpio) sub-chronically exposed to perfluorooctanoic acid

An operator-neutral, objective method was implemented to comparatively assess liver pathology in 30 specimens of common carp (Cyprinus carpio): 20 after experimental flow-through exposure to two perfluorooctanoic acid (PFOA) dosages (10 fish exposed to 200 ng l⁻¹ and 10 fish exposed to 2 mg l⁻¹) for 56 days and 10 unexposed (negative control). The method relies on texture analysis as a complementary approach to traditional histopathology and chemical dosage analysis performed previously on the same experimental material. Texture features data were analyzed by means of Redundancy Analysis (RDA), Linear Discriminant Analysis (LDA) and Canonical Variates Analysis (CVA). LDA resulted in the correct classification of 80% of cases (24 out of 30 cases) with a sensitivity of 83.3% and a specificity of 83.3. In particular, four male samples from the low dosage group (200 ng l⁻¹) were misclassified as unexposed fish and two female samples from the unexposed group were misclassified as low dosage exposed. Nevertheless, PFOA liver chemical dosage analysis results were the same both in unexposed and in low dosage group fish, all below the limit of detection. No sample from the high dosage group (2 mg l⁻¹) has ever been misclassified. Interestingly, texture features correlated with the PFOA concentrations detected in the liver of each sampled fish. In the present study the technique of texture analysis was combined with techniques of multivariate exploratory data analysis (RDA, LDA/CVA). This approach resulted in a robust, sufficiently sensitive and specific means to study PFOA-induced liver pathology. The new method can discriminate between unexposed and two PFOA exposed groups with better confidence and in a more affordable way, compared to chemical quantification of liver PFOA. The texture features correlated well with liver PFOA concentrations and objectively quantified degenerative liver morphology. In conclusion the overall approach may be a suitable candidate as a reliable and broad-ranging method for biomarker analysis of exposure and effect.     

Remote estimation of canopy height and aboveground biomass of maize using high-resolution stereo images from a low-cost unmanned aerial vehicle system

Canopy height (H_canopy) and aboveground biomass (AGB) of crops are two basic agro-ecological indicators that can provide important indications on the growth, light use efficiency, and carbon stocks in agro-ecosystems. In this study, hundreds of stereo images with very high resolution were collected to estimate H_canopy and AGB of maize using a low-cost unmanned aerial vehicle (UAV) system. Millions of point clouds that are related to the structure from motion (SfM) were produced from the UAV stereo images through a photogrammetric workflow. Metrics that are commonly used in airborne laser scanning (ALS) were calculated from the SfM point clouds and were tested in the estimation of maize parameters for the first time. In addition, the commonly used spectral vegetation indices calculated from the UAV orthorectified image were also tested. Estimation models were established based on the UAV variables and field measurements with cross validation, during which the performance of the UAV variables was quantified. Finally, the following results were achieved: (1) the spatial patterns of maize H_canopy and AGB were predicted by a multiple stepwise linear (SWL) regression model (R² = 0.88, rRMSE = 6.40%) and a random forest regression (RF) model (R² = 0.78, rRMSE = 16.66%), respectively. (2) The UAV-estimated maize parameters were proved to be comparable to the field measurements with a mean error (ME) of 0.11 m for H_canopy, and 0.05 kg/m² for AGB. (3) The SfM point metrics, especially the mean point height (H_mean) greatly contributed to the estimation model of maize H_canopy and AGB, which can be promising indicators in the detection of maize biophysical parameters. To conclude, the variations in spectral and structural attributes for maize canopy should be simultaneously considered when only simple RGB images are available for estimating maize AGB. This study provides some suggestions on how to make full use of the low-cost and high-resolution UAV stereo images in precision agro-ecological applications and management.     

Diversity and spatial clustering of shade trees affect cacao yield and pathogen pressure in Costa Rican agroforests

The importance of the spatial organisation of individuals in explaining species coexistence within a community is widely recognised. However, few analyses of spatial structure have been performed on tropical agroforests.The main objective of this study was to highlight the links between spatial organisation of shade trees on the one hand, and shade tree species richness and cacao yield on the other, using data from 29 cacao agroforests in Costa Rica.A method of spatial statistics, Ripley's K-function, was used to analyse the spatial organisation of shade and cacao trees in the study plots. For each stand, the X and Y coordinates of ≥2.5-m-tall trees were recorded. In each plot we also assessed shade tree species richness and cacao yield (with total number of pods = number of pods damaged by frosty pod rot + number of healthy pods).Three types of stands were identified: the first was characterised by significant clustering of shade trees, the highest shade tree species richness (S = 6), and the highest number of damaged pods (139 pods ha^?1 year^?1). The second type was characterised by random spatial organisation of shade trees. The third type showed a trend towards regular organisation. Species richness of shade trees did not differ significantly between the last two types (S = 4 for both), nor did the number of damaged pods (56 pods ha^?1 year^?1 and 67 pods ha^?1 year^?1 respectively).Although the trends were not statistically significant for all the variables in our data set, the clustered spatial structure appears to favour a synergy between environmental (tree species richness), and provisioning (cacao production) services.     

Managing road corridors to limit fire hazard. A simulation approach in southern France

Road corridors are sources of fire ignition and fire spread in French Mediterranean areas, but little is known about the flammability of vegetation and the probability of fire ignition and spread to neighbouring forests. This study simulated fire propagation in road corridors with the help of a cellular automata (CA). We assessed the relative importance of vegetation type, fuel treatment and the spatial patterning of vegetation on the probability of fire spreading to forests. The cellular automaton simulator was implemented with different types of corridors (30 m × 40 m), on the basis of an extensive field survey of vegetation. We used data from laboratory flammability experiments to determine the probability of ignition and propagation for each of the 20 cm × 20 cm cells of the CA. The probability of a fire reaching the neighbouring forest (P_FR) indicated that certain types of road corridors represent a very high risk owing to a combination of highly flammable vegetation and high spatial connectivity. The lowest P_FR values correspond to corridors with a decreasing vegetation flammability gradient in the vicinity of the forest. A several meter-wide embankment with low-flammable and/or managed vegetation can substantially reduce P_FR. These results suggest that firewise landscaping and local vegetation management can reduce fire risk in road corridors. Each corridor type should be subjected to specific vegetation management to account for flammability, growth pattern and lifetime.     

Leaf non-structural carbohydrates regulated by plant functional groups and climate: Evidences from a tropical to cold-temperate forest transect

Non-structural carbohydrates (NSCs), e.g., glucose and starch, play important roles in metabolic processes of plants and represent important functional traits in plant's adaptation to external environment. To explore the variations in leaf NSCs among species and communities at a large scale and their influencing factors, we investigated the contents of leaf NSCs among 890 plant species in nine typical forests along the north–south transect of eastern China. The results showed that the contents of leaf soluble sugars, starch, and NSCs (sugars + starch) were highly variable among different plant species on the site scale, and their mean values for the 890 plant species were 45.7 mg g⁻¹, 47.5 mg g⁻¹, and 93.2 mg g⁻¹, respectively. All three metrics varied markedly across plant functional groups in the order of trees < shrubs < herbs. Weak latitudinal patterns of leaf soluble sugars, starch, and NSCs were observed from tropical to cold-temperate forests at the levels of species and plant functional groups. The contents of leaf soluble sugars, starch, and NSCs decreased with increasing temperature and precipitation which supports the growth limitation hypothesis at a large scale. In trees, leaf soluble sugars, starch, and NSCs increased with increasing photosynthetic active radiation (PAR); and were positively correlated with specific leaf area (SLA). The spatial patterns of leaf NSCs in forests along the north–south transect of eastern China and their relationships with temperature, precipitation, PAR, and SLA illustrate an important adaptation of plant communities to environmental changes at the continental scale.     

Post-fire dynamics of woody vegetation in seasonally flooded forests (impucas) in the Cerrado-Amazonian Forest transition zone

Fire disturbance alters the structural complexity of forests, above-ground biomass stocks and patterns of growth, recruitment and mortality that determine temporal dynamics of communities. These changes may also alter forest species composition, richness, and diversity. We compared changes in plant recruitment, mortality, and turnover time over three years between burned and unburned sites of two seasonally flooded natural forest patches in a predominantly savanna landscape (regionally called ‘impucas’) in order to determine how fire alters forest dynamics and species composition. Within each impuca, 50 permanent plots (20 m × 10 m) were established and all individuals ≥5 cm diameter at breast height (DBH) identified and measured in two censuses, the first in 2007 and the second in 2010. Unplanned fires burned 30 plots in impuca 1 and 35 in impuca 2 after the first census, which enabled thereafter the comparison between burned and unburned sites. The highest mortality (8.0 and 24.3% year⁻¹ for impuca 1 and 2) and turnover time (69 and 121.5 years) were observed in the burned sites, compared to 3.7 and 5.2% year⁻¹ (mortality), and 28.4 and 40.9 years (turnover), respectively, for the unburned sites. Although these seasonally flooded impuca forests are embedded in a fire-adapted savanna landscape, the impucas vegetation appears to be sensitive to fire, with burned areas having higher mortality and turnover than unburned areas. This indicates that these forest islands are potentially at risk if regional fire frequency increases.     

Effects of dwarf bamboo (Fargesia denudata) density on biomass, carbon and nutrient distribution pattern

Dense dwarf bamboo population is a structurally and functionally important component in many subalpine forest systems. To characterize the effects of stem density on biomass, carbon and majority nutrients (N, P, K, Ca and Mg) distribution pattern, three dwarf bamboo (Fargesia denudata) populations with different stem densities (Dh with 220 ± 11 stems m^?2, Dm with 140 ± 7 stems m^?2, and Dl with 80 ± 4 stems m^?2, respectively) were selected beneath a bamboo-fir (Picea purpurea) forest in Wanglang National Nature Reserve, Sichuan, China. Leaf, branch, rhizome, root and total biomass of dwarf bamboo increased with the increase of stem density, while carbon and nutrient concentrations in bamboo components decreased. Percentages of below-ground biomass and element stocks to total biomass and stocks decreased with the increase of stem density, whereas above-ground biomass and element stocks exhibited the opposite tendency. Moreover, more above-ground biomass and elements were allocated to higher part in the higher density population. In addition, percentages of culm biomass, above-ground biomass and element stocks below 100 cm culm height (H₁₀₀) increased with the increase of stem density, while percentages of branch and leaf biomass below H₁₀₀ decreased. Pearson’s correlation analyses revealed that root biomass, above-ground biomass, below-ground biomass and total biomass significantly correlated to leaf biomass in H_100?200 and total leaf biomass within high density population, while they significantly correlated to leaf biomass in H_50?150 within low density population. The results suggested that dwarf bamboo performed an efficient adaptive strategy to favor limited resources by altering biomass, carbon and nutrients distribution pattern in the dense population.     

Spatial pattern model of herbaceous plant mass at species level

Individual plant species distribute according to their own spatial pattern in a community. In this study, we proposed an index for measuring the spatial heterogeneity in mass (dry weight) of individual plant species. First, we showed that the frequency distributions for mass of individual plant species per quadrat in a plant community are expressed using the gamma distribution with two parameters of λ (mean) and p. The parameter p is a measure indicating the level of spatial heterogeneity of plant mass as follows: (1) when p = 1, the plant mass per quadrat has a random pattern; (2) when p > 1, the plant mass has a spatial pattern with a lower heterogeneity than would be expected in the random pattern; and (3) when p < 1, the plant mass has a spatial pattern with a higher heterogeneity than would be expected in the random pattern. The p value for a given species can easily be calculated by the following equation if we use the moment method: (mean plant mass among quadrats)² / (variance of plant mass among quadrats). The scatter diagram of (λ, p) for individual plant species, exhibits the spatial characteristics of each species in the community. We illustrated two examples of the (λ, p) diagram from data for individual species composing actual communities in a semi-natural grassland and a weedy grassland. Frequency distributions for the plant mass of individual species per quadrat followed the gamma distribution, and indi vidual species exhibited an inherent level of spatial heterogeneity.     

Characterization of the toxicity of Cochlodinium polykrikoides isolates from Northeast US estuaries to finfish and shellfish

Harmful algal blooms caused by Cochlodinium polykrikoides are annual occurrences in coastal systems around the world. In New York (NY), USA, estuaries, bloom densities range from 10³ to 10⁵ mL^?1 with higher densities (≥10⁴ cells mL^?1) being acutely toxic to multiple fish and shellfish species. Here, we report on the toxicity of C. polykrikoides strains recently isolated from New York and Massachusetts (USA) estuaries to juvenile fish (Cyprinodon variegates) and bay scallops (Argopecten irradians), as well as on potential mechanisms of toxicity. Cultures of C. polykrikoides exhibited dramatically more potent ichthyotoxicity than raw bloom water with 100% fish mortality occurring within ～1 h at densities as low as 3.3 × 10² cells mL^?1. More potent toxicity in culture was also observed in bioassays using juvenile bay scallops, which experienced 100% mortality during 3 days exposure to cultures at cell densities an order of magnitude lower than raw bloom water (～3 × 10³ cells mL^?1). The toxic activity per C. polykrikoides cell was dependent on the growth stages of cultures with early exponential growth cultures being more potent than cultures in late-exponential or stationary phases. The ichthyotoxicity of cultures was also dependent on both cell density and fish size, as a hyperbolic relationship between the death time of fish and the ratio of algal cell density to length of fish was found (～10³ cells mL^?1 cm^?1 yielded 100% fish mortality in 24 h). Simultaneous exposure of fish to C. polykrikoides and a second algal species (Rhodomonas salina or Prorocentrum minimum) increased survival time of fish, and decreased the fish mortality suggesting additional cellular biomass mitigated the ichthyotoxicity. Frozen and thawed-, sonicated-, or heat-killed-, C. polykrikoides cultures did not cause fish mortality. In contrast, cell-free culture medium connected to an active culture through a 5 μm nylon membrane caused complete mortality in fish, although the time required to kill fish was significantly longer than direct exposure to the whole culture. These results indicate that ichthyotoxicity of C. polykrikoides isolates is dependent on viability of cells and that direct physical contact between fish and cells is not required to cause mortality. The ability of the enzymes peroxidase and catalase to significantly reduce the toxicity of live cultures and the inability of hydrogen peroxide to mimic the ichthyotoxicity of C. polykrikoides isolates suggests that the toxicity could be caused by non-hydrogen peroxide, highly reactive, labile toxins such as ROS-like chemicals.     

Spatial requirements of jaguars and pumas in Southern Mexico

Understanding how large felids use space is essential for the design of conservation plans that are required for their survival. Jaguars (Panthera onca) and pumas (Puma concolor) are the largest felids in the Neotropics, and they are sympatric throughout the entire range of the jaguar. However, there is very little information about the spatial requirements of these two species in the tropical rainforests of Central America. Using satellite GPS collars, we compared the spatial ecology of jaguars and pumas in a tropical rainforest in southern Mexico. We found that jaguars had home ranges that were 2–6 times larger than those of pumas. The mean annual home range was 181.4 ± 4.0 km² for female jaguars and 431.6 ± 152.6 km² for males. Annual home range for the only female puma tracked was 34.3 km², and 72.0 ± 85.2 km² for males. Jaguars and pumas with overlapping home ranges showed little overlap of core areas and avoided using the same sites at the same time, which suggested that territoriality and avoidance were in play. Further evidence of avoidance was derived from our observation that pumas exhibited greater movement during the lightest periods of the day and jaguars moved most during the darkest. This temporal separation probably facilitates coexistence. Our data suggest that habitat destruction and fragmentation has more severe effects on jaguars than on pumas. According to our estimates, patches of at least 180 km² of primary forest are required to meet the annual spatial requirements of female jaguars. Thus, to conserve jaguars in this region, large tracts of primary forest should be preserved. Importantly, this population of jaguars depends on the adequate preservation of connectivity between natural reserves in Mexico and Guatemala.     

Locomotion at –1.0°C: burst swimming performance of five species of Antarctic fish

We investigated the burst swimming performance of five species of Antarctic fish at −1.0°C. The species studied belonged to the suborder, Notothenioidei, and from the families, Nototheniidae and Bathydraconidae. Swimming performance of the fish was assessed over the initial 300 ms of a startle response using surgically attached miniature accelerometers. Escape responses in all fish consisted of a C-type fast start; consisting of an initial pronounced bending of the body into a C-shape, followed by one or more complete tail-beats and an un-powered glide. We found significant differences in the swimming performance of the five species of fish examined, with average maximum swimming velocities (U_max) ranging from 0.91 to 1.39 m s⁻¹ and maximum accelerations (A_max) ranging from 10.6 to 15.6 m s⁻². The cryopelagic species, Pagothenia borchgrevinki, produced the fastest escape response, reaching a U_max and A_max of 1.39 m s⁻¹ and 15.6 m s⁻², respectively. We also compared the body shapes of each fish species with their measures of maximum burst performance. The dragonfish, Gymnodraco acuticeps, from the family Bathdraconidae, did not conform to the pattern observed for the other four fish species belonging to the family Nototheniidae. However, we found a negative relationship between buoyancy of the fish species and burst swimming performance.     

Variation in stable isotope (δO and δC) signatures in the sagittal otolith carbonate of king threadfin, Polydactylus macrochir across northern Australia reveals multifaceted stock structure

Otoliths of king threadfin, Polydactylus macrochir were collected from 2007 to 2009 at nine locations across northern Australia representing most of their distributional range and areas where fisheries are active. Measurement of the stable isotope ratios of δ¹⁸O and δ¹³C in the sagittal otolith carbonate from assemblages of P. macrochir revealed location-specific signatures and indicated that adult fish sampled from representative sites across their range were significantly different. The significant differences in the isotopic signatures of P. macrochir demonstrated that population subdivision is evident and there is unlikely to be substantial movement of fish among these distinct adult assemblages. The stable isotopic signatures for the fish from the different locations were persistent through time, and therefore it could be concluded that they comprise separate stocks for many of the purposes of fisheries management. The spatial separation of these populations indicates a complex stock structure across northern Australia with stocks of P. macrochir associated with large coastal beaches and embayments on a fine spatial scale. These results indicate that in order to achieve optimal fisheries management, the current spatial management arrangements need to be reviewed, particularly the potential for localised depletion of stocks on small spatial scales. This study has provided further evidence that measurement of the stable isotopes ratios in teleost sagittal otolith carbonate can be a valuable tool in the delineation of fishable stocks or fishery management units of adult fish and that widely distributed fish can nonetheless show strong localised population structure.     

Neighbourhood analysis as an indicator of spatial requirements of broiler chickens

The appropriate stocking density for broiler chickens is a much discussed topic in animal welfare. To determine at which stocking density the level of crowding becomes aversive to 4–6-week-old broiler chickens, spatial distribution and behaviour of groups stocked at 8, 19, 29, 40, 45, 51, 61 or 72 birds per 3.3 m² were analysed. Spatial distribution was evaluated using three different indices: inter-individual distances, nearest neighbour distances and Dirichlet polygon areas. The assumption was that broilers would increase the distance to their pen mates if high densities (i.e., close proximity to pen mates) were experienced as aversive, whereas they would decrease this distance if close proximity was experienced positively. Increased distances to pen mates would lead to increased nearest neighbour distances and a more homogeneous distribution (i.e., lower variation of inter-individual distances and of Dirichlet-polygon size) than expected by chance. The distribution expected by chance was determined from both a random distribution and a ‘resource-corrected’ random distribution (which incorporated environmental influences on spatial distribution but excluded social ones).Behavioural observations showed that at higher stocking densities more sitting bouts (P = 0.003) and adjustments of the sitting and lying posture (P < 0.001) occurred. It was also found that nearest neighbour distance varied according to behaviour (P = 0.001). Birds that were eating/drinking were further apart from their nearest neighbour than birds that were foraging, preening, adjusting their sitting or lying posture or showing “other” behaviour.The results from all three methods of spatial analysis suggested that broilers in groups ≥19 birds per 3.3 m² (ultimately equivalent to 15 kg/m²) started to experience the proximity of conspecifics as aversive at some point during the last 3 weeks of rearing. However, nearest neighbour distance analysis showed evidence of aversiveness earlier in life than the other methods of analyzing spatial distribution (variation in inter-individual distance and polygon size), suggesting that nearest neighbour distance is the more sensitive indicator of space requirements.When uneven use of the different areas within the pen was reflected in the expected distribution (i.e., for comparisons to the resource-corrected random distribution) different results were obtained than when such measures were omitted (i.e., for comparisons to the random distribution). As such, this study emphasises the importance of accounting for environmental influences on distribution within a pen.