Texas A&M findings could lead to improved breeding conditions
It is well known that in man, as well as other mammals, the temperature of the scrotal sac is normally maintained a few degrees below mean body temperature. This phenomenon maintains the integrity of sperm, for sustained elevated temperature in testes reduces sperm count and increases the percentage of abnormal sperm.
Interestingly, a study recently conducted at the Texas Agricultural Experiment Station, Shrimp Mariculture Project of the Texas A&M University System in Port Aransas, Texas, USA showed that temperature also affects the sperm quality of Pacific white shrimp (Litopenaeus vannamei), the most commercially important shrimp species in the Americas.
Groups of male broodstock with a mean weight of 47.9 grams were exposed to water temperatures of 26, 29 and 32 degrees-C for 42 days. The experiment was conducted under controlled laboratory conditions, meeting high standards for water quality. The sperm quality of the shrimp, as determined by sperm count and percentage of abnormal sperm, was evaluated at initiation and termination of the experiment.
Animals held at 26 degrees-C showed a more than twofold increase in sperm counts with respect to the initial value, while the sperm quality of shrimp kept at the higher temperatures was deeply affected, rendering the animals sterile. Sperm collected from these organisms consisted mainly of pieces of disrupted sperm cells, resulting in dramatically decreased sperm counts (Fig. 1).
As a result of the extensive deterioration of sperm, the percentages of abnormal sperm increased to very high values for these organisms. In fact, all or almost all sperm were abnormal. In contrast, the percentage of abnormal sperm from shrimp maintained at 26 degrees-C remained almost constant (Fig. 2).
The marked sensitivity to deterioration of sperm quality at high water temperature by L. vannamei shown in this study can contribute to an improvement of breeding conditions for this species. Also, the results have direct relevance for rearing sub-adult male shrimp for reproduction purposes, especially for maintenance of male-only populations.
The temperature-sensitive nature of sperm has been reported for other shrimp species like L. setiferus and L. stylirostris, as well as a number of mammals. Perhaps the specific mechanisms for heat-induced deterioration of male fertility in these varied animals are similar. This is an area that deserves further research.
(Editor’s Note: This article was originally published in the December 2002 print edition of the Global Aquaculture Advocate.)
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