Decreased genetic diversity and a reduced effective population size in cultured silver-lipped pearl oysters (Pinctada maxima)

Before selection programmes for aquaculture species can commence, a fundamental knowledge of how the culture process affects genetic diversity is requisite. “South Sea” pearl production, through the culture of the silver-lipped pearl oyster, Pinctada maxima, stands to gain substantially from genetic selection. Aquaculture techniques for P. maxima have progressed vastly, to a point where the majority of current operations are based on hatchery-propagated stock; however, there has been no investigation on how the culture process is affecting the genetic diversity of this species. To address this deficiency, we investigated the genetic diversity and effective population sizes (N_e) in three wild and five hatchery-produced P. maxima populations. Using six microsatellite DNA markers, cultured populations exhibited low N_e (3.5–9.2) and reduced allelic richness (29–44%) compared with their wild progenitors. Observed heterozygosities were not affected greatly, however, an increased mean pairwise genetic relatedness was observed in all cultured populations. The practice of mass spawning was identified as a major factor in the reduction of diversity, although diversity was not necessarily maintained when a more controlled spawning approach was utilised. Pedigree reconstructions revealed genetic diversity and N_e is affected by large skews in full-sib family representations (up to 40% from a single family, in a cohort using 28 broodstock), and could be due to differential survival rates amongst communally reared families. In order to maximise future selective breeding efforts, further research should be directed towards identifying critical stages of the culture process in which genetic diversity is lost.     

Modellstudien zur Nitratauswaschung unter beweidetem Grünland

Modeling nitrate leaching from grazed pasture A method for estimating nitrate concentrations in seepage water under pastures using the model WASMOD was developed. Urin-N and dung-N input by grazing cattle was calculated as a function of stocking rate, length of grazing, and amounts of urin-N and dung-N excreted (data from literature). Urin-N was modeled as NH₄⁺-fertilizer, dung-N as fresh organic matter (C/N ratio 18.6:1). The model was tested using average stocking rates on pastures and mowing pastures inside the waterworks ‘Föhr-West’ catchment area and a long-term climate scenario (35 yr). The modeled average nitrate concentration (55.5 mg l⁻¹) agreed well with the average nitrate concentration measured in the public wells (59.5 mg l⁻¹). Model studies indicate that the nitrate concentrations in seepage water can be reduced by 40% if the cattle graze only 9 hours per day and no longer than until mid of September.     

Discrimination of haploid and diploid maize kernels via multispectral imaging

The use of doubled haploids (DHs) in maize has become ubiquitous in maize breeding programmes as it allows breeders to go from cross to evaluation in as little as 2 years. Two important aspects of the in vivo DH system used in maize are as follows: (i) the identification of haploid progeny and (ii) doubling of the haploid genome to produce fertile inbred lines. This study is focused on the first step. Currently, identification of maize haploid progeny is performed manually using the R1‐nj seed colour marker. This is a labour‐intensive and time‐consuming process; a method for automated sorting of haploids would increase the efficiency of DH line development. In this study, six inbred lines were crossed with the maternal haploid inducer ‘RWS/RWK‐76’ and a sample of seed was sorted manually for each line. Using the VideometerLab 3 system, spectral imaging techniques were applied to discriminate between haploids and hybrids. Using DNA markers to confirm the haploid/diploid state of the tested seed, for the majority of genotypes haploid identification was possible with over 50% accuracy.     

Diurnal feeding pattern and gut content of milkfish Chanos chanos (Forsskål, 1775) cultured semi‐intensively during the wet and dry season in brackish ponds in the Philippines

To improve feeding management and reduce feed cost in semi‐intensive grow‐out culture of milkfish (Chanos chanos, Forsskål 1775) in brackish ponds, the relative shares of natural food (NF) and supplemental feed (SF) ingested by the fish were microscopically quantified from their completely dissected digestive tracts sampled during 24‐h cycles in wet (June–September) and dry (December–April) seasons. Particles from rice husk, indigestible to milkfish, were used as internal markers to quantify supplemental feed. Significantly (P<0.05) more NF than SF (1.4±0.2 vs. 0.4±0.1 g kg^?0.8) and SF than NF (1.4±0.8 vs. 0.6±0.3 g kg^?0.8) were found during the first month of the wet and the first 3 months of the dry season respectively. Diurnal feeding patterns on SF were significantly higher at morning hours during the dry compared with the wet season. The feeding pattern of milkfish is likely to be affected by the different weather and pond conditions in both seasons. Developing a season‐specific pond fertilization management to enhance NF availability in semi‐intensive milkfish culture can help to improve the economical and ecological performance of milkfish culture.     

The incorporation of environmentally derived 87Sr/86Sr and Sr/Ca in early otolith formation of Chinook salmon

Effective species management often requires understanding patterns of movement and habitat use. A common approach in identifying where individuals reside relies upon chemical tracers from the environment that are incorporated into an individual's tissues. For fish, isotopes in their otoliths, specifically the portion of their otolith formed during their larval stage, have been used to identify the natal origin. Complicating this work, however, is the fact that during this life stage, there is a shift in the source of isotopes deposited onto the growing otolith from maternally to environmentally derived. The objective of this study was to identify the portion of the otolith representing this transition to environmentally derived isotopes so as to accurately investigate questions of natal origin for a threatened population of fall Chinook salmon (Oncorhynchus tshawytscha). We exposed developing larvae to four treatments that differed in terms of their water strontium isotope ratio (⁸⁷Sr/⁸⁶Sr) and used change-point analysis of otolith ⁸⁷Sr/⁸⁶Sr and strontium to calcium ratio (Sr/Ca) to identify the otolith radius corresponding to the transition to environmentally derived isotopes. Our results indicated this transition occurred, on average, at 132 μm (⁸⁷Sr/⁸⁶Sr; ±50 μm standard deviation) and 127 μm (Sr/Ca; ±29 μm) from the otolith core, which corresponded to the developmental time between hatching and exogenous feeding. A substantial proportion of our otoliths (i.e., 61%) did not show convergence between otolith and water ⁸⁷Sr/⁸⁶Sr by the end of the 113-day experiment, which was likely due to the dietary contribution of marine-based feed. Therefore, we were unable to recommend an otolith radius to target for the purposes of reconstructing natal origin apart from being beyond approximately 130 μm.     

Characterization of Durum Wheat Semolina by Means of a Rapid Shear‐Based Method

A rapid shear‐based test (the GlutoPeak test, recently proposed by Brabender) was used to investigate gluten aggregation properties of durum wheat semolina and to relate them to pasta cooking behavior. Thirty semolina samples were characterized by means of the conventional approaches used for pasta‐quality prediction (protein content, gluten index, and alveographic indices). All samples were also analyzed by the GlutoPeak test, obtaining three parameters: maximum peak torque, maximum peak time, and area under the peak. The GlutoPeak indices were significantly correlated with protein content, gluten index, and W alveographic parameter. The cooking quality of pasta obtained from the 30 semolina samples was evaluated by sensory analysis in terms of stickiness, bulkiness, firmness, and overall quality. The GlutoPeak indices were significantly correlated with the sensorial parameters. In comparison with the alveographic test, which is presently the most used rheological approach for semolina characterization, GlutoPeak analysis presents some advantages represented by a smaller amount of sample (9 g), a shorter time (less than 5 min), and the possibility that untrained analysts can carry it out. In addition, following testing with larger sample numbers, the GlutoPeak test has the potential to be used instead of the gluten index as a rapid and reliable approach for medium‐quality semolina characterization.