Effects of dietary astaxanthin source and light manipulation on the skin colour of Australian snapper Pagrus auratus (Bloch & Schneider, 1801)

Two experiments were conducted with Australian snapper Pagrus auratus (Bloch and Schneider, 1801). The first was aimed at determining the dietary level of astaxanthin that improved skin redness (CIE a^*values) of farm‐reared snapper. Farmed snapper (ca. 600 g) fed a commercial diet without carotenoids were moved to indoor tanks and fed the same diet supplemented with 0, 36 or 72 mg astaxanthin kg^?1 (unesterified form as Carophyll Pink?) for nine weeks. Skin redness (CIE a^* values) continued to decrease over time in fish fed the diet without astaxanthin. Snapper fed the diet containing 72 mg astaxanthin kg^?1 were significantly more red than fish fed the diet with 36 mg astaxanthin kg^?1 three weeks after feeding, but skin redness was similar in both groups of fish after 6 and 9 weeks. The second experiment was designed to investigate the interactive effects of dietary astaxanthin source (unesterified form as Carophyll Pink? or esterified form as NatuRose?; 60 mg astaxanthin kg^?1) and degree of shading (0%, 50% and 95% shading from incident radiation) on skin colour (CIE L^*a^*b^*) and skin and fillet astaxanthin content of farmed snapper (ca. 800 g) held in 1 m³ floating cages. After 116 days, there were no significant interactions between dietary treatment and degree of shading for L^*, a^* or b^* skin colour values or the concentration of astaxanthin in the skin. Negligible amounts of astaxanthin were recovered from fillet samples. The addition of shade covers significantly increased skin lightness (L^*), possibly by reducing the effect of melanism in the skin, but there was no difference between the lightness of fish held under either 50% or 95% shade cover (P>0.05).     

Investigation of the nutritional requirements of Australian snapper Pagrus auratus (Bloch & Schneider, 1801): effects of digestible energy content on utilization of digestible protein

This study used a curvilinear model to investigate the effects of different digestible energy (DE) levels on the digestible protein (DP) requirements of juvenile snapper Pagrus auratus. For each DE level (15, 18 or 21 MJ kg⁻¹), DP content was increased from about 210–560 g kg⁻¹ in seven evenly spaced increments by formulating a summit diet (highest DP content) and a diluent diet (lowest DP content) at the desired DE level and combining the summit and diluent diets in various ratios to achieve the desired DP content. This ensured the DE level remained relatively stable. Each of the 21 dietary treatments was fed to three replicate groups of snapper twice daily to apparent satiation for 57 days. At the completion of the trial, fish were weighed and killed for chemical analysis. Results indicated that the rapid growth of snapper weighing 30–90 g was highly dependent on the ratio of DP to DE and that optimum protein deposition did not occur until snapper were offered feeds with at least 350 g DPkg⁻¹, irrespective of DE level. According to the fitted models, diets formulated for snapper reared at temperatures from 20–25°C should contain approximately 23 g DP MJ DE⁻¹ to promote optimal weight gain and protein deposition. Based on the feeding regime used in this study, this could be achieved with practical diets containing a DP:DE ratio of 460:20, 420:18 or 350:15.     

The use of repellents to reduce predation of tree seed by wood mice (<Emphasis Type="Italic">Apodemus sylvaticus</Emphasis> L.) and grey squirrels (<Emphasis Type="Italic">Sciurus carolinensis</Emphasis> Gmelin)

The loss of tree seed through predation by granivores can be a major cause of regeneration failure in direct seeding systems. Five repellents that were of low toxicity or derived from foodstuffs were investigated for their ability to deter feeding by wood mice (Apodemus sylvaticus L.) and grey squirrels (Sciurus carolinensis Gmelin). In experiments in controlled conditions, when given the option of feeding on unlimited amounts of untreated wheat (Triticum aestivum L.), or wheat treated with aluminium ammonium sulphate, sulphonated fish oil, denatonium benzoate, ziram or capsaicin, all the repellents tested initially deterred feeding, although in one experiment mice showed some habituation to the repellents after 4 weeks. Capsaicin was the most effective treatment, and aluminium ammonium sulphate the least effective, possibly because it did not stick to the wheat grains. When ash (Fraxinus excelsior L.) seed were treated with combinations of aluminium ammonium sulphate, sulphonated fish oil or denatonium benzoate, compared to the freely available untreated seed, mice were deterred by any treatment containing aluminium ammonium sulphate, with effectiveness again declining after 4 weeks. When a mixture of broadleaved tree species were sown on farmland, coating seed with aluminium ammonium sulphate or sulphonated fish oil had no effect on seedling emergence. Capsaicin derived from chilli peppers (Capsicum sp.) showed the greatest potential as a repellent in our work, but no repellent product containing this active ingredient is currently approved for plant protection uses in the United Kingdom. Given its relatively low cost, the use of aluminium ammonium sulphate, a non-toxic repellent based on an approved food additive, which is available formulated as a registered plant protection product in the United Kingdom, may be worth considering for direct sowings where predation pressure from mice is predicted to be particularly high, or where tree species with very palatable seed are being used, to complement other predation mitigation strategies.     

Restocking with broadleaved species during the conversion of Tsuga heterophylla plantations to native woodland using natural regeneration

The removal of conifers planted during the twentieth century on sites that had been woodland for many centuries, with the intention of restoring native broadleaved species, is an important aim of forestry policy in Great Britain. Current guidance generally advocates gradual removal of plantation trees using continuous cover silviculture and restocking by natural regeneration, but methods are largely untested. This study investigated natural regeneration of trees and shrubs at sites where western hemlock had been established either pure or in mixture with native broadleaved species. Western hemlock had been cleared from 70% of the sites. There were c. 10?C300 stems ha^?1 providing canopy cover of 10?C90%; the predominant broadleaved canopy trees were ash, beech, birch and oak. The ground flora of all sites was species poor; bramble was the predominant vegetation type overall, but grasses, rushes and shrubs were relatively more abundant on open sites. A total of 15 native tree species were regenerating, birch was most common and at most sites there were few valuable broadleaved timber species. Although combined numbers of seedlings and saplings varied from 200 to 20,000 ha^?1, large areas of most sites had few regenerating trees and <10% of their area was becoming restocked with timber species. Relationships between seedling numbers and site characteristics were complex and varied with species, but there was a consistent positive relationship between the presence of nearby parent trees and the frequency and abundance of seedlings. The results indicate that the current reliance on natural regeneration may be unwise especially for those broadleaved species such as oak and beech which are valued for their timber.     

Does water-stress lead to formation of traumatic tissue and tracheid collapse in poorly lignified Pinus radiata?

Copper deficiency and stem deformation have been linked to poor lignification in Pinus radiata and in non-woody species. Tracheid collapse in zones of poorly lignified woody tissue from deformed Pinus radiata has also been reported. This paper reports an experiment to investigate whether tracheid collapse in poorly lignified wood from Cu-deficient plants can be caused by water-stress.

Seedlings from two families of P. radiata were grown in a peat/sand mix and subjected to stages of water-stress after symptoms of stem and branch deformation had become apparent. The final stage of water-stress was sufficient to kill the seedlings.

Woody tissue was poorly lignified, and seedlings had very low concentrations of copper in foliage (1.1 μg g⁻¹). However, collapsed tracheids were not evident in poorly lignified wood after water-stress had been applied. The results indicated that previously reported tracheid collapse in deformed and poorly lignified stems of P. radiata was not caused by water-stress.

There were significant differences in stem deformation between the two seedling families.     

A rapid and simple method of detection of <Emphasis Type="Italic">Blepharisma japonicum</Emphasis> using PCR and immobilisation on FTA paper

Background  

The rapid expansion in the availability of genome and DNA sequence information has opened up new possibilities for the development of methods for detecting free-living protozoa in environmental samples. The protozoan Blepharisma japonicum was used to investigate a rapid and simple detection system based on polymerase chain reaction amplification (PCR) from organisms immobilised on FTA paper.