Seaweed extracts as a natural control against the monogenean ectoparasite,Neobenedenia sp., infecting farmed barramundi (Lates calcarifer)

Aqueous extracts from common tropical seaweeds were evaluated for their effect on the life cycle of the commercially important ectoparasite, Neobenedenia sp. (Platyhelminthes: Monogenea), through the survival of attached adult parasites, period of embryonic development, hatching success and oncomiracidia (larvae) infection success. There was no significant effect of any extract on the survival of adult parasites attached to fish hosts or infection success by oncomiracidia. However, the extracts of two seaweeds, Ulva sp. and Asparagopsis taxiformis, delayed embryonic development and inhibited egg hatching. The extract of A. taxiformis was most effective, inhibiting embryonic development of Neobenedenia sp. and reducing hatching success to 3% compared with 99% for the seawater control. Furthermore, of the 3% of eggs that hatched, time to first and last hatch was delayed (days 14 and 18) compared with the seawater control (days 5 and 7). Asparagopsis taxiformis shows the most potential for development as a natural treatment to manage monogenean infections in intensive aquaculture with the greatest impact at the embryo stage.     

Hybridization of biotinylated oligo(dT) for Eukaryotic mRNA quantitation

Quantitation of mRNA content in samples of total cellular RNA is required for the analysis of Northern blot hybridization to estimate the relative level of specific gene expression. Commonly used methods based on UV absorbance and dye staining measure only total RNA, and mRNA normalization by probing for mRNA levels of housekeeping genes, such as β-actin and glyceraldehyde-3-phosphate dehydrogenase, assumes a constant level of their expression, which, in fact, may vary as a function of cell proliferation and differentiation. We describe here a nonradioactive, slot-blotting method for quantifying eukaryotic mRNA levels using a biotinylated oligo(dT) probe, which hybridizes directly to the 3′-polyadenylated sequence of eukaryotic mRNAs. The method provides a more accurate estimation of mRNA content in total RNA samples and should be applicable for quantitative Northern analysis.     

Comparative production and nutritional value of “sea grapes” — the tropical green seaweeds Caulerpa lentillifera and C. racemosa

“Sea grapes” is a collective term for the edible varieties of the green seaweed genus Caulerpa. Here we conduct comparative analyses of the biomass productivities and biochemical properties of C. lentillifera and C. racemosa from tropical Australia. Commercial-scale production was evaluated using 1 m² culture units with high stocking densities (>5 kg m^?2). Productivity of C. lentillifera in a 6-week period yielded, on average, 2 kg week^?1, whereas C. racemosa yielded <0.5 kg week^?1. Morphometric comparisons of the harvestable biomass revealed that C. lentillifera had a higher proportion of fronds (edible portions) to horizontal runners (stolons) and a higher density of fronds per unit area. C. racemosa fronds, however, were significantly longer. The nutritional value of C. racemosa was higher than C. lentillifera for both polyunsaturated fatty acids (10.6 vs. 5.3 mg g^?1 DW) and pigments (9.4 vs. 4.2 mg g^?1 DW). The content of eicosapentaenoic acid (EPA) and β-carotene decreased with increasing frond size in both species. Trace element contents also varied substantially between the species, including higher levels of zinc, magnesium and strontium in C. lentillifera, and higher levels of selenium in C. racemosa. Some less desirable elements were higher in C. lentillifera, including arsenic (1 vs. 0.1 ppm) and cadmium, whereas others were higher in C. racemosa, including lead, copper and vanadium. Overall C. lentillifera has a high biomass production potential in monoculture and distinct nutritional properties that warrant a focus on its commercialisation as a new aquaculture product in tropical Australia and in Southeast Asia more broadly.