In Vitro Degradation of Poly(caprolactone)/nHA Composites

The degradation behavior and mechanical properties of polycaprolactone/nanohydroxyapatite composite scaffolds are studied in phosphate buffered solution (PBS), at 37 degrees C, over 16 weeks. Under scanning electron microscopy (SEM), it was observed that the longer the porous scaffolds remained in the PBS, the more significant the thickening of the pore walls of the scaffold morphology was. A decrease in the compressive properties, such as the modulus and the strength of the PCL/nHA composite scaffolds, was observed as the degradation experiment progressed. Samples with high nHA concentrations degraded more significantly in comparison to those with a lower content. Pure PCL retained its mechanical properties comparatively well in the study over the period of degradation. After the twelfth week, the results obtained by GPC analysis indicated a significant reduction in their molecular weight. The addition of nHA particles to the scaffolds accelerated the weight loss of the composites and increased their capacity to absorb water during the initial degradation process. The addition of these particles also affected the degradation behavior of the composite scaffolds, although they were not effective at compensating the decrease in pH prompted by the degradation products of the PCL.

Degeneration of postovulatory follicles in the Iberian sardine Sardina pilchardus: structural changes and factors affecting resorption

Inaccuracy in the aging of postovulatory follicles (POFs) and in estimating the effect of temperature on the resorption rate of POFs may introduce bias in the determination of the daily spawning age classes with the daily egg production method (DEPM). To explore the above two bias problems with f ield-collected European pilchard (Sardina pilchardus, known regionally as the Iberian sardine), a method was developed in which the time elapsed from spawning (POF age) was estimated from the size of POFs (i.e., from the cross-sectional area in histological sections). The potential effect of the preservative type and embedding material on POF size and the effect of ambient water temperature on POF resorption rate are taken into account with this method. A highly significant loglinear relationship was found between POF area and age; POF area shrank by approximately 50% per day. POFs were also shown to shrink faster at higher temperatures (approximately 3% per degree), but this temperature effect is unlikely to be an important source of bias in the assignment of females to daily spawning classes. The embedding material was also shown to influence the size of POFs, the latter being significantly larger in resin than in paraffin sections. In conclusion, the size of POFs provides an indirect, reliable estimation of the time elapsed from spawning and may thus be used to test both the validity of POF staging criteria for identifying daily classes of spawners and the effect of other factors (such as temperature and laboratory processing) in applications of the DEPM to S. pilchardus and other fish species.

Simple broodstock management to control indirect selection and inbreeding: Indian carp example

Following a survey of the important traits of Indian carp broodstock at some southern Indian hatcheries, it was found that the broodstock selection was size selective, exerting strong, negative selection of prematuration growth rate and positive selection on age at first maturation. This meant that the hatchery bred inadvertently slower growing and later maturing individuals. Details are given of approaches to avoid such negative selection and minimize inbreeding.

Magnetoelectric metallic glass/polymer laminated composites: from fabrication to applications

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Indirect validation of the age-reading method for Pacific cod (Gadus macrocephalus) using otoliths from marked and recaptured fish

Two examples of indirect validation are described for age-reading methods of Pacific cod (Gadus macrocephalus). Aging criteria that exclude faint translucent zones (checks) in counts of annuli and criteria that include faint zones were both tested. Otoliths from marked and recaptured fish were used to back-calculate the length of each fish at the time of its release by using measurements of the area of annuli. Estimated fish size at time of release and actual observed fish size were similar, supporting the assumption that translucent zones are laid down on an annual basis. A second method for validating reading criteria used otolith age and von Bertalanffy parameters, estimated from the tagging data, to predict how much each fish grew in length after tagging. We found that otolith aging criteria applied to otoliths from tagged and recovered Pacific cod predicted quite accurately the growth increments that we observed in these specimens. These results provide further evidence that the current aging criteria are not underestimating the age of the fish and support our current interpretation of checks (i.e., as subannual marks). We expect these indirect validations to advance age determination for Pacific cod, which in turn would enhance development of stock assessment methods based on age structure for this species in the eastern Bering Sea.