MATURATION WITHOUT ABLATION
From : Lorenzo Juarez Ljuarez@seafarmsgroup.com
Sent: 15 January 2003
I was wondering if we could have the group's ideas on
what are the promising avenues for obtaining commercial vannamei maturation
without the need for eyestalk ablation. Some possibilities would be:
selective breeding, special feeds, manipulation of environmental conditions, hormones,
etc. If I remember correctly, a few years ago I was told that the highly
selected stocks of stylis in Venezuela did not require ablation for
commercial maturation. Can anyone comment on this? Has anyone tested
specialty feeds, temperature/photoperiod regimes, and/or hormonal
supplements with no ablation in a commercial maturation situation?
Lorenzo M. Juarez
Sea Farms International
GMSB Shrimp Hatchery
Summerland Key, FL. USA
(305) 745-3738 ext. 11.
There are (unpublished) examples of ovarian
maturation of un-ablated L. vannamei. Hatcheries involved in selective
breeding do indeed report that a substantial % of their broodstock reaches
fully mature stages "spontaneously" after some generations in
captivity, which I think is normal in any domestication process. They also
reach maturity at lower body weights than their wild counterparts. In a
breeding program, feeding and culture conditions during pond-growing and
pre-maturation will largely decide if un-ablated broodstock can mature
optimally and if they are fit for the reproductive process.
In theory, hormones should also do the trick. Methyl farnesoate, largely described by Hans Laufer, is apparently not keeping up the promises. Endocrinology is as complicated as the word itself, and we can only hope for a major break-through by one of the few researchers addressing this topic (the identification of the major reproductive hormones, the production of these hormones at industry scale, the delivery to the broodstock animals, ...).
At the time I was doing research at CENAIM in Ecuador, we compared the reproductive performance of pond-reared Venezuelian L. vannamei from an advanced breeding generation, with wild L. vannamei from the Santa Elena Peninsula. About 30% of the Venezualian broodstock was in maturity stage 1, 2 or 3 upon arrival from the ponds. We only selected immature animals to proceed and kept both groups (pond-reared and wild) on the same diets during 2 to 3 weeks. The maturity stage was the same in both groups after these two weeks (pre-ablation), and the maturation frequency was also the same in the post-ablation period. However, half of both groups was fed a regular diet, and the other half was fed a good diet, and a statistically significant effect of the diet was detected pre- and post-ablation. You have guessed it, the point I am trying to make is that broodstock nutrition is an important issue that may over-rule other factors (genetics, hormones). Additionally, the nutrition of the pond-reared animals during on-growing is also interfering: once entered in the maturation facilities, animals with a poor initial nutrition condition (body reserves) will be affected much faster by an eventual imbalanced or incomplete broodstock diet formulation. Wild animals, on the other hand, have access to a variety of marine food organisms like gastropods, bivalves, crustaceans, polychaetes and plant material, increasing the possibility that all necessary nutrients for optimal performance under maturation conditions are provided.
I could not agree more with Roeland's comments and
observations. We have a long way to go before we can achieve hormonal
reproduction in shrimp and in my experience it has been difficult to
obtain grant funding for basic research in this area. One of the big
problems is the cost of maturation research and the difficulty in
operating enough tanks in a research setting to overcome inherent
variability. Clearly the basics must be in place as a prerequisite to
maturation performance and nauplii quality. This includes nutrition as
a major factor and a wide range of physical and environmental parameters which end up making maturation more of an art than a science in many cases. The confounding part is that in my experience most of these myriad factors work synergistically such that when things go wrong it is very difficult to troubleshoot in a stepwise controlled fashion. It should be noted as well that maturation success in general and success without ablation in particular varies greatly between species.
Examples of successful commercial scale nauplii production without
ablation are few and far between although some groups contend that they have had success, particularly with stocks bred for many generations in captivity. In captive breeding programs one often selects for reproductive performance because it is obviously only the shrimp that reproduce that make it to the next generation. In breeding programs which target large numbers of families in a short period of time this selection pressure is increased. This has resulted in improved
maturation performance. However, a cautionary note should be voiced in that selection for reproductive performance even if unintentional has
the potential to either work synergistically, antagonistically or have
no effect on other traits of interest. For example there are examples
in the literature where selection for gonad weight had a negative effect
on growth and other production characteristics in fish.
Having said all of this it has been my experience that if maturation
system management and design is optimal, there is little to be gained by elimination of unilateral eyestalk ablation. There is an increasing
body of evidence suggesting that given optimal maturation conditions,
ablated females can produce high quality offspring for months with
little or no negative effects other than a small reduction in spawn
size. With improving diets this trend should be enhanced. The only
advantage that I see would be use of broodstock for more extended
periods of time. The significance of this would depend upon the
economies of broodstock procurement.
Craig L. Browdy
President - World Aquaculture Society
Marine Resources Research Institute
South Carolina Department of Natural Resources
217 Ft. Johnson Rd. (P.O. Box 12559)
Charleston, SC 29422