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Size Matters in Spermatophore Production
A Discussion from the Shrimp List
Glen Bieber (email@example.com): Much has been written about the minimum breeding size for male Penaeus monodon. With so much domestication work being done, what are the minimum size, length and weight for males to produce mature spermatophores?
I am working with P. monodon broodstock in Tanzania, East Africa. We are growing animals for the purpose of domestication, but in the meanwhile, we continue to fish for wild broodstock. I have referred to publications from years ago, Motoh (1981) and Primavera (1988), that say both pond raised and wild males need to weigh at least 40 grams to produce mature sperm.
Alain Michel (firstname.lastname@example.org): If you look at the different strains of P. monodon around the world, you will discover that the size differences from Fiji, the eastern end of monodon’s range, and Madagascar, the western end of its range, are extremely large. The strain from Fiji has males half the size of females of the same age. In this strain, after several generations in captivity, some males as small as 20 grams produced fertile spermatophores. This was probably caused by the fact that we were selecting for the fastest growing shrimp and for the ones that reached sexual maturation the earliest. We observed the same thing in New Caledonia with P. stylirostris. After more than 30 generations in captivity, males matured at 40 grams, while wild strains don’t mature until they reach 70 grams.
Nelson Gerundo (email@example.com): Glen, you forget to mention that Primavera (1988), citing Motoh (1981), wrote that P. monodon reached sexual maturity in ponds at a carapace length of 31 millimeters, compared to wild males that reached sexual maturity at 37 mm. Here’s the reference: http://repository.seafdec.org.ph/bitstream/handle/10862/865/biol.monodon_p037-057.pdf?sequence=1
Also, here is a link to more recent work by Teikwa and Mgaya (2003) on the abundance and reproductive biology of P. monodon and P. indicus from the coastal waters of Tanzania. They mentioned sexual maturity in giant tiger shrimp at a carapace length 35 mm for males and 43 mm for females: http://www.oceandocs.org/bitstream/1834/960/1/WIOJ22117.pdf
For those who might not be familiar with carapace length, it is measured anteriorly from the fifth spine of the rostrum in P. vannamei and from the third and the fourth rostral spine in P. monodon (or at about the base of the eyestalk in both) going backward to the posterior margin of the carapace. Here is a link to this reference: http://fsf.fra.affrc.go.jp/chow/paper/PvannameiGrowth.pdf
To measure shrimp carapace length, it is ideal to use a plastic or stainless steel caliper like the one shown in the second picture in the following link: http://scientistsatsea.blogspot.com/2011_03_01_archive.html.
Chandran Ravi (firstname.lastname@example.org): Glen, for P. monodon, fertilization is more effective when the males are 70 to 75 grams.
Nelson Gerundo (email@example.com): Chandran Ravi, although weight is more exacting, carapace length is probably easier for fieldwork because only a caliper is required. You just hold the animal down and measure it. Scales are more cumbersome and, if you’re working with live animals, you can’t hold the animal down, and it will probably jump all over the place.
Glen, according to the Queensland Department of Primary Industries and Fisheries (2006), as cited by Nguyen Duy Hoa (2009), wild P. monodon mature at an age of 5-12 months at a body weight of 35 to 50 grams for males and 68 to 75 grams for females. In one of his breeding experiments, Nguyen Duy Hoa found that the use of older and heavier males resulted in a slightly higher hatching success. Like Chandran Ravi (above), Nguyen Duy Hoa reported using males weighing 70-80 grams, as shown on Table 7, Page 112 in the following link: http://www.phdportal.ugent.be/partners/ugent/2009-12-04-nguyen_duy_hoa/popup/FullThesis.pdf
Glen, Shi-Gui-Jiang (et al., 2009) reported that the minimum P. monodon carapace length for sexual maturation was between 3.1 and 3.2 millimeters, with a minimum body length between 11.1 and 11.5 millimeters and a minimum body weight between 19.9 and 24.2 grams. Here’s the link to this reference: http://www.sciencedirect.com/science/article/pii/S0044848609002993.
Following is a link to the latest work done by Gay Marsden, Neil Richardson, Peter Mather and Wayne Knibb (2013) in Australia on the reproductive behavioral differences between wild-caught and pond-reared P. monodon broodstock. Note that in this study, Gay Marsden (et al.) wrote: “Further, all-male P. monodon used in the current study were above 70 grams, which was shown by Jiang (et al., 2009) to be the average minimum weight for males to possess viable sperm, signifying sexual maturity.” Page 9, Lines 344-346: http://eprints.qut.edu.au/59872/1/
Jim Wyban (firstname.lastname@example.org): In my 15-year breeding program with specific pathogen free P. monodon, we found that males below 40 grams will not mate. While artificial insemination with P. monodon is possible, I don’t think it’s advised as a commercial breeding strategy. Generation by generation, we saw dramatic improvement in captive mating behavior in all our domesticated shrimp stocks (vannamei, stylirostris, monodon and japonicus).
David Currie (email@example.com): I can't find the reference (maybe it was the British Museum), but I think the standard method for carapace measurement of shrimp is from the post-orbital margin (the front edge of the concave curving bit behind the eye) to the rear of the carapace in the midline. It can only really be measured accurately using a caliper. Measuring from the rostral teeth may be less accurate, given some variability in the relative positions of the rostral teeth and some difficulty in deciding precisely where to line up with one of them.
Glen Bieber (firstname.lastname@example.org): Everyone, I really appreciate the above information on artificial insemination and fertility of males. I have found that artificial insemination is much easier with P. vannamei than it is with P. monodon, especially when it comes to the removal of the spermatophore.
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