Date: 28 Oct 1997
From: Bunmi Jimi <bunmij@hotmail.com>
To: aqua-l@killick.ifmt.nf.ca
QUESTION:
I am working on the captive maturation of Penaeus merguiensis using
live diets, adult Artemia, squid and a polychaetous annelid (Diopatra
sp.).
The problem is that while the shrimps were able to mature and spawn, the eggs were not viable (failed to hatch).
Could anyone out there offer any suggestions for the failure of
the eggs to hatch?
Olubunmi Akinfolajimi
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COMMENTS 1:
Date: 28 Oct 1997
From: Ronaldo Cavalli <Ronaldo.Cavalli@UGent.be>
To: AQUA-L@killick.ifmt.nf.ca
There is a lot of possibilities, but the first thing that comes to my mind is that your females didn't mate. Since P. merguiensis is a closed
thelycum species, you can easily find it out by checking the thelycum. It should present a whitish color, which characterizes the presence of the spermatophore. Lack of mating may be due to several factors, such as unfavorable female-male ratio, noise/stress (specially during mating hours), small tank size, etc...
Ronaldo O. Cavalli
Laboratory of Aquaculture & Artemia Reference Center
University of Gent
Rozier 44
9000 Gent Belgium
Phone: + 32 9 264.3754 E-mail: Ronaldo.Cavalli@UGent.be
Fax: + 32 9 264.4193
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COMMENTS 2:
Date: 28 Oct 1997
From: Bunmi Jimi <bunmij@hotmail.com>
To: aqua-l@killick.ifmt.nf.ca
The ratio of male to female is 1.3:1 (more males than females) and
I 'm using four 10-ton tanks. Actually, I did observe spermatophore
presence in some of the females (not all though).
I feed each tank with a separate diet i.e. I am using single item diet
for each tank. Could this have had any effect on the viability of the
eggs, especially as I ablated the shrimps (both unilaterally and
bilaterally)?
Olubunmi
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COMMENTS 3:
Date: 29 Oct 1997
From: Ronaldo Cavalli <Ronaldo.Cavalli@UGent.be>
To: AQUA-L <AQUA-L@killick.ifmt.nf.ca>
It would be interesting to know which are the food items you are
using. It is well documented that some fatty acids (FA) play an important role on the hatching of penaeid eggs (we also have data showing the same trend in Macrobrachium rosenbergii), but my guess is that the effect of FA would be just to decrease a bit the percent hatch. I think that if you observed no hatching at all, this is probably related to mating itself.
What is your tank diameter? Since it is a 10-ton tank, it probably
has at least 3 meters. Am I correct? Penaeids need a certain "run
distance" for their mating ritual. If this is not provided, mating will
hardly occur.
As I mentioned before, environmental stress, specially noise caused by pumps or humans, also affect mating. This is specially true if
any daily routine, such as feeding, siphoning and/or cleaning of the
tanks, are done during peak mating hours (usually between 18 to 24 h, if you don't use an inverse photoperiod). This should be carefully considered, because you will find no biological explanation to your problem.
Consider also the source of your animals. Are they wild-caught?
If so, in the open sea or from a shallow bay? Are they pond-reared? Under which conditions? For how long? How big are they?
Did you notice any difference between the percentage hatch of
unilaterally and bilaterally ablated females? This might be the source of your problem. Why did you ablate females bilaterally? I think you will observe a high mortality among bilaterally ablated females. When you ablate, you cause several physiological changes which cause a severe stress in the animal. Though an increase on the reproductive activity is observed, most of these changes are not directly related to reproduction and will certainly affect your females.
Above all, keep in mind that there might not be just one cause to
the problem, but maybe a sum of causes. Try to improve all the possible sources of "problems" you might find.
Ronaldo O. Cavalli
Laboratory of Aquaculture & Artemia Reference Center
University of Gent
Rozier 44
9000 Gent Belgium
Phone: + 32 9 264.3754 E-mail: Ronaldo.Cavalli@UGent.be
Fax: + 32 9 264.4193
***************
COMMENTS 4:
Date: 29 Oct 1997
From: dfegan@t-rex.hatyai.inet.co.th
To: AQUA-L <AQUA-L@killick.ifmt.nf.ca>
Ronaldo & Jimi,
In closed thelycum species, ovarian development doesn't take place unless mating has occurred. If you got eggs, they did mate, so I would look elsewhere for the answer. In open thelycum species, on the other hand, mating takes place after ovarian maturation so the explanation given by Ronaldo may be valid. I'm afraid I can't remember offhand if P. merguiensis is open or closed thelycum, so I can't say if Ronaldo simply got the two mixed up.
Daniel Fegan
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COMMENTS 5:
Date: 4 Nov 1997
From: Ronaldo Cavalli <Ronaldo.Cavalli@UGent.be>
To: AQUA-L@killick.ifmt.nf.ca
Dear Daniel & aquafriends,
It was really good to have your comments on this issue. I had to
take a look back in some papers to be able to send you this reply. I was doing the great mistake of taking things for granted.
Back to that issue... Though I have no experience with merguiensis, it is a closed thelycum species. For closed thelycum penaeids, some papers report that a lack of mating results in the spawning of unfertilized gametes. Whether this is really due to the lack of mating, bad sperm quality, or any other factor is to be discussed.
It might be that gonadal development is triggered/stimulated by male contact/copulation, though sperm transfer doesn't actually take place... For penaeids, the only study I was able to trace back was that of Peeters & Diter (1994) in which they demonstrated that impregnated (and non-ablated) P. indicus females spawned more frequently than non-impregnated females. This means that gonadal development of intact females is indeed influenced by impregnation. However, it also shows that for non-impregnated females gonadal development occurred, but at a smaller rate than for impregnated females.
Another interesting conclusion drawn from the same study was that
when females were ablated, the "impregnation effect" disappears, i.e.,
non-mated females spawned with the same frequency as mated ones. It seems that the effects of ablation and impregnation are similar on maturation and spawning.
Ronaldo O. Cavalli
Laboratory of Aquaculture & Artemia Reference Center
University of Gent
Rozier 44
9000 Gent Belgium
Phone: + 32 9 264.3754 E-mail: Ronaldo.Cavalli@UGent.be
Fax: + 32 9 264.4193
***************
COMMENTS 6:
Date: 4 Nov 1997
From: Craig Browdy <browdycl@musc.edu>
To: AQUA-L@killick.ifmt.nf.ca
In my experience, open and closed theycum penaeids continue to spawn regardless of the presence or absence of spermatophores. This is particularly true following unilateral eyestalk ablation.
In response to Olubunmi Akinfolajimi's original query, low fertilization and hatch are likely a result of a combination of factors and I have suggested that he go back to basics and do a complete review of his systems. Factors such as tank size, lighting, noise, water quality, broodstock age and health, feed quality, etc. all can affect mating success or spawn quality in one way or another often synergistically.
Craig L. Browdy
Waddell Mariculture Center
POB 809
Bluffton, SC 29910 USA
Phone: 803-837-3795
FAX: 803-837-3487
Email: browdycl@musc.edu