Dennis Meadows, one of the original authors of Limits to Growth, thinks it is far too late to achieve sustainable development, as that term is commonly understood. The Limits to Growth, one of the first scholarly works to recognize that the world was approaching its sustainable limits, turns 40 this year. Speaking at a joint [...]

Publication year: 2012
Source: Aquaculture, Available online 4 February 2012

Eli D. Aflalo, Raju V.S.N. Dandu, Naidu A. Bommi, Johny T. Verghese, Thampi Y.C. Samraj, ...

Sex reversal technology, realized through androgenic gland (AG) manipulation, was recently introduced as a process for production of all-male producing broodstock. This technology exploits however, a relatively small number of sex-reversed broodstock. Thus, both genetic improvement via a breeding program and prevention of inbreeding are needed to ensure the sustainability of such technology. Three wild strains of prawns originating from geographically (though not necessarily genetically) isolated locations in India [Gujarat (G), Kerala (K) and West Bengal (WB)] were assessed for their suitability as breeders for all-male production. In addition, their potential for a selective breeding program was evaluated. A comparative evaluation of early sex segregation, sex reversal, growth performance, and population structure in the three selected strains was performed. Among the purebred strains, after eight months of grow out in earthen ponds, growth performance of the WB strain was the best (59.39 ± 1.08 g), while that of G was the poorest (26.50 ± 0.94 g). Strain-additive genetic effects for body weight at harvest were highest for the WB strain (+ 45.9%) and lowest for the G strain (− 28.3%). Body masses of WB × K and WB × G crosses were 14.2% and 8.8% above the mean mass of the purebred strains, respectively, while that of the K × G cross was 23% below this value. In most crosses, males reached heavier mean body weights than did females with higher frequencies of the large male morphotypes being seen in the WB purebred strain and its respective crosses. Reciprocal effects for body mass ranged from 4% to 14.9% below the mean of the purebred strains. These negative signs mean that in the two crosses involving the WB strain, growth performance is higher when this stain was used as the sire strain. Similarly, the growth performance of the K × G cross was higher when the former was used as the sire strain. Average heterosis effect for body weight was minor (− 0.51 ± 0.73) and did not differ significantly from zero. The high correlation between strain additive effects (the major source of variation in growth) and total performance for body weight (r = 0.927) indicate the existence of valuable genetic variation that could be exploited in a selective breeding program. For all-male production, males from the three strains were segregated at early post-larval stages and microsurgical AG removal was performed. In all the strains, similar low levels of complete sex reversal into functional neo-females (genetic males) were realized (0.17% − 0.34%). These produced relatively small numbers of neo-female to be crossed with normal males to produce the desired all-male population, but raise the possibility that such a process could result in a genetic bottleneck. Thus, a genetic improvement scheme for each strain integrated with periodical crosses of the resulting neo-females from one strain with males from another strain is suggested to avoid inbreeding.

Highlights

â–º Culturing all-male prawns presents one of the most promising avenues for increasing yield and income. â–º Three Indian geographically isolated strains of prawns were assessed for their suitability for all-male culture. â–º After eight months of grow out in earthen ponds, growth performance of the West Bengal strain was the best. â–º Androgenic glad ablated Juvenile males from the three strains transformed into functional neo-females. â–º Neo-females from one strain crossed with selected males from another strain suggested for future monosex culture.

Publication year: 2012
Source: Aquaculture, Available online 3 March 2012

Shyamalie D. Senadheera, Giovanni M. Turchini, Thanongsak Thanuthong, David S. Francis

The complete and successful replacement of fish oil in aquafeed without compromising fillet omega-3 long chain polyunsaturated fatty acid (n-3 LC-PUFA) concentrations has yet to be achieved. As means of overcoming this issue, the potential ofin vivon-3 LC-PUFA biosynthesis in cultured fish has been widely investigated and may permit the future economical and sustainable development of aquaculture. Two of the key enzymes involved in this process include the fatty acid Δ-6 and Δ-5 desaturases, where, in the terminal protein of each complex, iron is present in the active di-iron centres. To the best of authors’ knowledge, no investigations have thus far been attempted to elucidate the potential roles of dietary iron on the fatty acid metabolism of cultured fish. In this study, graded inclusions of dietary iron were tested in rainbow trout fed vegetable oil based diets. This study generated preliminary evidence suggesting that dietary iron concentration can have a positive effect on LC-PUFA biosynthesis in fish and data are herein reported. In particular, dietary iron level was shown to affect the final n-3 LC-PUFA content of fish tissues and also to modulate the activity of fatty acid desaturase enzymes. This activity was insufficient to compensate for a diet lacking in LC-PUFA but does highlight potential strategies to maximise this activity in cultured fish fed fish oil free diets.

Highlights

â–º Iron plays an important role in the active centres of fatty acid desaturase enzymes. â–º Is dietary iron affecting LC-PUFA biosynthesis in fish fed fish oil free diets? â–º Dietary iron level affected the final n-3 LC-PUFA content of fish tissues. â–º Preliminary evidences that iron modulates the activity of desaturases were reported. â–º This increased activity was insufficient to compensate for diets lacking in LC-PUFA.

Publication year: 2012
Source: Carbohydrate Research, Available online 3 March 2012

Gregory L. Côté