Date: 27 August 1998
To: AQUA-L@killick.ifmt.nf.ca
QUESTION:
Normally, the Chinese freshwater crab Eriocheir sinensis mature in the second year. However, with the development of crab farming, most of the crabs mature in the first year. The matured crabs only have a body weight of 30-50 grams, which is much less than the market weight. Some scientists in China indicate that the reasons are higher temperature, good feeds, higher density, etc. We want to know what are the real or main reasons of precocious ovarian maturation of crab? And how to prevent this phenomenon? Any information and literatures are very much appreciated.
Liu Fengqi
Dept. of Biology
Nankai University
Tianjin 300071
China
Tel/Fax: +86-22-2369-1856
<fengqi@mail.zlnet.com.cn>
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COMMENTS 1:
I have nothing to share about crabs, but there is an analagous early maturation phenomenon in crayfish that can be reduced by increased feed and decreased density (Romaire et al., 1979. Growth and survival of stunted red swamp crayfish (Procambarus clarkii) in a feeding-stocking density experiments in Pools. Fresh Water Crayfish 4: 331-336).
Stunting is also seen in the other crayfish (Hunter and Lindqvist, 1986. A stunted crayfish (Astacus astacus) population in central Finland. Freshwater Crayfish 6: 156-165), and may occur when larger crayfish apparently inhibit subordinates growth. It is related to poor water quality (Curtis and Jones, 1995. Overview of red crayfish (Cherax quadricarinatus, farming practices in northern Australia. Freshwater Crayfish 10: 456-468).
There is some evidence that there is a minimum number of molts to maturity in P. clarkii. If they mature at the minimum number of molts they are stunted, conversely, if they molt more than the minimum number of times they are larger and more marketable. Aquaculturists are managing crayfish farms to produce larger crayfish by manipulating population density and food.
I suspect that the early molt to maturity in crayfish is an adaptation that increases the chance of reproduction in an environment that is subject to rapid change. Perhaps your crabs are maturing early because of poor water quality, a high population density (social inhibition?) or sub-optimal feeding.
Dave O'Neill, doneill@dundalk.cc.md.us
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COMMENTS 2:
Penaeid shrimp have a growth inhibiting hormone in the eye stalks. Researchers have reported growth enhancement by removal of one or more eye stalks. Perhaps penaeids could serve as a model for the
Chinese crab in this regard. For more info, you might contact:
Dr. Don Lightner
email: aquapath@ccit.arizona.edu
As you're probably already aware, extrinsic factors affecting reproduction include photoperiodicity, temperature, current, presence of the opposite sex, etc. In some fishes, the tide and stage of the moon are factors.
Kent Hauck, agmain.khauck@state.ut.us
Fish Pathologist