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Ablating Broodstock

A Discussion from the Shrimp List

 

  Eyestalk ablation (cutting off one eyestalk) is a technique for hormonally inducing ovarian maturation in shrimp.  It reduces the concentration of gonadal-inhibiting hormone that is secreted from the X-organ-sinus gland complex in the eyestalk and has the effect of stimulation ovarian maturation...George Chamberlain from The Shrimp Book.  

 

Jeff Prochaska (jeffepro@hotmail.com): I would like to know if anybody has tried ablating male Penaeus vannamei broodstock to induce mating?

 

Occassionally, you see a batch of males that doesn’t seem interested in mating, even when they appear mature and have no visible signs of spermatophore melanization or other health problems.  Sometimes these males are held for a longer period, and their female counterparts are mated with an older batch of males, or males and females from different batches or sources are simply swapped to induces mating behavior.  This is, of course, not ideal for production because you may not always have an older batch, or multiple batches to swap around.

 

The question of male ablation has come up over the years, but I’ve never heard of anybody actually doing it to get them to mate, and I’ve never had the opportunity to attempt it myself.  I have been laughed at when I ask the question, but it seems like a reasonable question to me.

 

Does anybody know from experience if ablation has any reproductive or other effects on males?

 

John Birkett (jbirkett42@yahoo.com): While marking males with hand-made eye-number tags, we accidentally severed or badly damaged the eyestalks of many males.  Successful matings from broodstock batches that include those males were not as good as batches that had males with undamaged eyestalks, even after the damages eyestalks had healed.

 

Josh Wilkenfeld (josh.wilkenfeld@gmail.com): Texas A&M did studies on male eyestalk ablation back in the early 1980s.  Look for articles by Joanna Trujillo and Bill Bray.  If I remember correctly, male eyestalk ablation did nothing to improve mating results.

 

Matthew Briggs (koygung101@yahoo.co.uk): Hi Jeff, for me the biggest problem in the maturation facility is the males.  With the normal ratio of one male for every female, I find that the males are usually unable to keep up with the females that have been ablated, so, especially towards the end of the maturation cycle (from 3 months onwards), there are a lot of females maturing and ready for mating and not enough males to do the job.

 

This is compounded by the fact that the males do not mature as quickly as females.  The best age for mating males is ten months and older, while females are ready for action at seven to eight months.

 

Males tend to last longer with fewer mortalities during the maturation cycle than females, but this does not compensate for their unwillingness to mate.  At the end of the cycle, when you start with a one-to-one male to female ratio, there is still a shortage of males and hence a lot of unmated and wasted females.

 

The reason for this is that you have artificially changed the maturation cycle of the females by ablating them.  They have no choice but to mature and spawn, while the males are on a natural maturation schedule, hanging out with their mates, not ready to get down to the business of chasing after females.

 

If you have the luxury of being able to stagger the batches, using older males with younger females, or buying extra males (difficult when most SPF animals are sold as pairs), then this problem can be alleviated.  This, however, is normally not the case.

 

I have read papers saying that ablation is unsuccessful for males, but there is also some work on methyl farnesoate which seems to contradict that finding.  There is even some research on injecting testosterone into the males, which did seem to work.  Check these studies [Editor: if these links don’t work, try copying and pasting them into your web browser and hitting return]:

 

Effect of Methyltestosterone and 17α-Hydroxyprogesterone on Spermatogenesis in the Black Tiger Shrimp, Penaeus Monodon Fab.

 

Effect of 17α-Methyltestosterone and 17α-Hydroxyprogesterone on the Quality of White Shrimp Penaeus vannamei Spermatophores

 

Because of this problem with the males, I did some research and came up with a product called “Spermaxx”, which I sell through Vannamei 101.  It’s a blend of plant extracts, minerals and vitamins known to increase, appetite sperm production and vigor.  It can be top dressed onto maturation diets.  This could help you out in lieu of more invasive techniques.

 

Anil Ghanekar (anilghanekar@yahoo.com): Great idea Matt—a Viagra-like aphrodisiac for male shrimp.  Why not develop a similar product for female shrimp, and we could do away with ablation.

 

How difficult would it be for broodstock suppliers to deliver older males or younger females?

 

Matthew Briggs (koygung101@yahoo.co.uk): Hi Anil, 17α-methyltestosterone injection of females has been shown to induce ovarian development.  However, I’m not recommending that because, as a “by-product” of selecting for growth and/or resistance, the process of domestication and selection has made it a lot easier to get females to mature and spawn without ablation, so spawning without ablation is possible, but not quite ready for full commercialization because we still want the most naups out of our females stocks that we can get and that, so far, is still achieved by ablation.

 

If, however, someone were to deliberately select for maturation without ablation, then I am 100% sure we could get there really quickly through selection alone.

 

Jeff Prochaska (jeffepro@hotmail.com): Thanks for all the comments.  Sounds like ablation isn’t the solution to the slower maturation process in male shrimp.  I agree that the magic age for male broodstock does appear to be about ten months for best performance.

 

The topic of determining the key factors for reproductive readiness (age, size, or both) and the impact of genetic selection for growth and other traits generation after generation would probably be a good line of research.  Vannamei breeding programs are operated in locations with a range of environments and temperatures that might impact growth and reproductive development of broodstock.  In warmer climates, do the broodstock grow faster and mature at an earlier age, or are they just larger at maturity?

 

If ten months is the best age for male broodstock, then they and especially the females of the same age may be too large to handle transport well.  Reducing growth rate, or staggering batches of broodstock to pair older males with younger females might be the answer.

 

Could we reduce the growth rate during broodstock growout?  Reducing the feeding rate might work, but that could potentially lead to under nourishment.  Lowering the temperature might work as well, but that could be expensive or impractical.

 

It would be interesting to look more closely at the potential for genetic improvement of reproductive traits in shrimp.  Studies have reported low to moderate heritability for some reproductive traits, implying the potential for improvement.  But, I don’t recall reading any reports of shrimp breeding programs successfully selecting for improved reproductive performance.  Perhaps we could potentially do away with ablation through genetic selection.  But, I imagine it would take a long time as breeders must focus on gains for traits of higher economic value (growth and disease resistance) and just hope to maintain reproductive performance.

 

If shrimp breeding programs utilized unablated females and natural mating, instead of artificial insemination, it might help to slowly improve reproductive performance.  It would require larger breeding populations to produce the required number of mature females, but that wouldn’t impact the rest of the program or trait selection, and it would be good for public relations.

 

Andy Watkins (andywathpc@gmail.com): Hi all, this is a very interesting discussion, and I would like to add a little information from my experience.

 

In a moment of true desperation when encountering males that were not interested in mating, we ablated them.  The reaction was not what we had hoped for; they simply sat on the bottom of the tank licking their wounds and decided that the abuse they had been put through was too much.  The last thing they wanted to do was mate.  I won’t do that again!

 

Regarding the reproductive age of the males, our experiences are very different from yours.  Our magic coming of age for the males is 140 days (about four and a half months).  As a rule we only keep our breeders until they reach 220 days (a little over seven months) when we consider them too old to be effective reproducers.  At ten months, they’re too large to transport effectively.  So we don’t keep our animals more than eight months.  Perhaps the difference is due to the fact that we have been actively selecting for reproductive performance for many years.  Our males at 300 days (10 months) would be overweight, senile and probably not be interested in chasing after females.

 

 Leonardo Tiro (lbtirojr@yahoo.com): Jeff and Matt, further to the discussion of not ablating female broodstock.  I would like to share my experience of producing nauplii from unablated females.  Early this year, I produced nauplii from 500 unablated females and an equal number of males, both from Global Gen, our broodstock facility.

 

Unablated females with ovarian stages between II to IV were selected and placed in the male tanks.  It is very interesting to note that males only mated with stage IV females.  Females at stages II and III rarely mated.  Although the mating rate was lower (average seven to eight percent a night) than for batches of ablated females, the nauplii from the unablated females were of a higher quality (active, highly pigmented and larger in size).  This test, which took five months, showed that it was commercially viable to produce nauplii from unablated females with very low daily mortality.

 

The postlarvae produced from the nauplii of unabalated females were quite uniform at PL-9, but the most significant result was their pond performance.  When harvested from an intensive farm using biofloc technology, they were surprisingly uniform in size, with an average weight of 20 grams after 70 days of growout.  Most of my PL market is with intensive farms, and I rarely received complaints about size variation at harvest from PLs produced from unablated females.

 

Matt, vannamei domestication and breeding has been done for over 15 years, and I believe it’s time to get back to the basics with broodstock.  We can produce nauplii commercially without ablation!  We might need to have a higher number of broodstock, like more than 500 females to produce 10-12 million naups a day.

 

There are other factors that have to be considered such as the right moist diets for broodstock.  Once the right mix or combination of diets has been developed, productivity from unablated females should be comparable to that of ablated females.  It is only a matter of time until low cost artificial moist diets for broodstock are developed.  When that happens, I hope the diets are better and cheaper.

 

Jeff, in some batches we can keep broodstock ablated at seven months in reproductive mode for up to five months with no affects on nauplii quality, but this is not true for all batches.

 

Daniel Gruenberg (seagardenfoods@mac.com): Leonardo, great work! I’m curious. It has been shown that certain dietary modifications have an effect on vitellogenesis and final maturation.

 

For example, diets containing high amounts of EPA (eicosapentaenoic acid) in a tank of UV treated water induce maturation in P. monodon, and vitamins like E and 5-HT (5-hydroxytryptamine) have been shown to significantly affect maturation in penaeids.  We ablate to reduce the serum levels of VIH (vitellogenin inhibiting hormone).  It appears the control of maturation is controlled by the balance of VIH and VSH (vitellogenin stimulating hormone).  Ablation tips the balance, or rather “forces” the balance in favor of VSH.  Since, in my opinion, this is a “hack” and since I serve a small niche market where consumers are concerned about the best possible animal welfare, I wonder if by adding some of the known examples of maturation induction other than ablation if you could further increase breeding performance in terms of fecundity and egg quality with less stress on the breeders.

 

 

Jeff Prochaska (jeffepro@hotmail.com): First, I want to make it clear that I’m speaking as an individual and not as a representative of a company or broodstock supplier.

 

My questions/comments are from experiences that I’ve had over the last ten years, or so, working with various populations of vannamei.  These experiences are primarily from breeding programs (not commercial maturation) utilizing artificial insemination (when individual parents weights and ages are known).

 

Artificial insemination (AI) with ten-month-old males resulted in more successful or larger spawns/hatches than with younger males.  This was very obvious when we reviewed our data to figure out why sometimes artificial insemination seemed easy and at other times difficult.  The spermatophores from older males were visibly larger, yielding a greater volume of sperm, which made AI easier (when using the sperm extraction method).  This may or may not be related to natural mating behavior, or to the actual quality of the sperm.  It could very well be true that these older individuals provided good sperm for AI, but they may not have been as eager to mate naturally as a younger males.  I just assumed that this meant the same would hold true in commercial maturation with natural mating.

 

I have not used AI for many years now, and don’t know if my previous observations would still hold true, or for which populations.  I assume, in general, shrimp populations haven’t changed that drastically regarding reproductive traits in a matter of four or five years, unless these reproductive traits have a higher heritability than I thought.  But, growth traits have increased significantly.

 

Andy, it’s encouraging to hear your report of success in selecting for and improving age at maturity.  It implies that performance of some reproductive traits could decrease if no selection pressure is placed on them, which is an important point.  I imagine there will be more attention and data in this regard as breeding programs mature.  When we have decades of well-documented breeding data, it will be interesting to look back and see (if it’s shared) what was significant.

 

It does sound like I have a pretty definitive answer regarding male ablation, without having to subjugate any shrimp to unnecessary anguish to satisfy my curiosity.  So, those shrimp say thanks.

 

Pamindangan Farm's Bocuan Orapopo (pamindangan@gmail.com): Does feeding polychaete worms improve the quality of the sperm/eggs of broodstock?

 

Bauman Hank (hank_bauman55@yahoo.com): Pamindangan Farms, with my limited knowledge of maturation (six years with vannamei) polychaetes are the magic feed.  They really make a difference.  I’ve been told by feed manufactures that some of the newer feeds work as well, but I’ve not tried them to date.

 

Pamindangan Farm's Bocuan Orapopo (pamindangan@gmail.com): Interesting points Hank, I threw that idea out there because polychaetes are what work in Indonesian hatcheries.  If you successfully combine the magical power of bloodworms and Spermaxx, we may be able to create shrimp orgies.

 

Matthew Briggs (koygung101@yahoo.co.uk): Thanks for your input Leonardo; your experience is always appreciated.

 

I agree that unablated females mature and spawn, but, as you say, they are not as productive as ablated spawners.  At most commercial hatcheries, this is a problem because SPF broodstock are a major expense.  The tendency is to try to get the most out of them as possible.  When your hatchery has its own broodstock supply company, it’s not much of an issue.

 

In Ecuador, back in the 1990s, when we were still using wild females, only four to five percent of our females spawned per night.  After a few generations of domestication and selection (not directly for spawning efficiency, but indirectly), the percentage rose to 10%, then to 15% or even 20% a night with animals from certain regions (notably Panama).

 

I find Leonardo’s comments on better nauplii quality and lower mortality from unablated females interesting.  That makes a difference and should be something breeding programs should strive for in the future.  From Andy’s post, it looks like he’s already there, so it must be doable.

 

Regarding Pamindangan Farm's point on polychaetes, in general, I would say that the more live polychaetes you feed the better your spawning results.  In China, for example, I recently saw broodstock being fed at 40% body weight per day on a diet of live polychaetes and good-quality, cold water (California) squid.  Those broodstock produced an average 400,000 nauplii per spawn for five months for total of seven million naups per broodstock pair over their active lifetimes.

 

In Ecuador, in the 1990s, we used to use local frozen polychaetes and productivity was never more than 120,000 to 150,000 naups per female, while in Thailand, increasing rates of feeding live polychaetes was correlated with increasing productivity up to 200,000 to 350,000 naups per female (after selection of good naups), so polychaetes clearly made a big difference.

 

I do not think that the polychaetes are as important for males as they are for females, but they still help.

 

Regarding alternatives to fresh feeds, I do believe we still have a ways to go.  None of the currently available diets are a complete replacement, but I do think that by adding a few bells and whistles to basic dry/moist broodstock diets (like vitamins, minerals, pigments, attractants and other supplements), we can provide better nutrition to the broodstock and get better naup quality.

 

One major problem has been the acceptance of dry diets.  This can be improved by making the diets by hand on site.  I find that adding an attractant like taurine helps.  Partially drying and freezing home-made diets helps produce a moist pellet that is much more accepted by the broodstock.  This way we can get the broodstock to eat 3-5% body weight per day, which does make a difference, especially to pigmentation and size of the ovary and hence naup quality.

 

John Birkett (jbirkett42@yahoo.com): Matt, because high mortalities of around 0.5% a day, Ecuador has always used a high rotation of animals in maturation.  The production of naups per female is about 120,000 a day.  A constant since we first noticed it ten years ago is that our unablated females from our microsatellite selections show two to three percent higher deformities (to my surprise) and six to eight percent lower mating rates than animals not selected by microsatellites.  We still keep unablated females because of their lower mortality rates and because of the high cost of female broodstock.

 

Selecting animals that come from ponds has resulted in:

 

• An increase in matings per day from 6% to 8% up to 16% to 20% per day.

• Early sexual maturation, probably from selecting big shrimp and feeding
them goodies from 15 grams on.

• An increase in growth.

• An increase in feed consumption from 18% to 20% to almost 30% of
body weight per day.

• A decrease in handling stress and the stress of being near humans.

• A decrease in nauplii deformity.

 

Leonardo Tiro (lbtirojr@yahoo.com): Daniel, thank you for your ideas.  I am sure feed companies are looking at these inputs to modify their maturation diets.  Most of the maturation diets, however, are very expensive.  Why not produce a modified moist maturation diet on site.  I am sure there are experts on this list that can provide some insights on how best to improve the diets.

 

Sources: 1. The Shrimp List (a mailing list for shrimp farmers).  Subject: Ablation of Male Broodstock.  June 25–29, 2013. 2. Bob Rosenberry, Shrimp News International, July 20, 2013

 

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