F. Santos, * D. Pratas, T. Baptista and A. Pombo
Marine Resources Research Group (GIRM), Polytechnic Institute of Leiria (Portugal)
*Email: 4130731@ipleiria.pt
Introduction
Sea cucumbers are presently exploited in industrialized, semi-industrialized and artisanal or small scale fisheries in more than 70 countries worldwide. They are exported regularly to Asian markets, as a fresh or processed product. Thus, sea cucumbers will be a new protein source for human consumption in the Occidental countries also (Purcell et al., 2012; González-Wangüemert et al., 2013).
However, it is necessary to develop sea cucumber aquaculture, inexistent in Portugal, to avoid over-exploitation of this resource in this country. In the Portuguese coast, there are some species with a vast potential for production, due to their nutritional value, such as Holothuria forskali and Stichopus regalis, nevertheless, it is necessary research to obtain information on the reproductive biology and life cycle (González-Wangüemert et al., 2013).
H. forskali is very resistant specie, found in intertidal, where environment conditions oscillate constantly. On the other hand, S. regalis is found in a wide depth range and it is presently consumed majority in Asia, where it is highly appreciated as a delicacy.
The study aims to evaluate sexual ratio on these two species using biopsy method, and observe the different maturity stages through macroscopic observation of gonads colour and histological observation of gametes.
Materials and Methods
Holothurian specimens were sampled in Portuguese Atlantic coast (39° 21′ 32″ N, 9° 22′ 40″ W). A number of 45 H. forskali individuals were collected by scuba diving and S. regalis were gathered by trawl method, in a total of 48 organisms. All specimens were conditioned in captivity, between October 2013 and June 2014. Ambient conditions were maintained equal to natural habitat. Temperature varied between 14ºC and 18ºC, 35 of salinity, sand bottom in an aerated recirculation system.
Sexual ratio was found using a biopsy needle to collect some gametes to microscopic observation, and identifying which specimens were males or females.
Maturity stages were analysed through macroscopic and microscopic observation. In first method, it was evaluated the gonads grade colorations, investigating seasonal patterns of gonad maturity, through monthly observations of gonadal tubules obtained from individuals, and in the second method, it was measured gametes diameter through OCM observations of histological sections coloured with hematoxylin-eosin.
Results
During conditioning period, mortality was not observed for H. forskali and it was approximately 19% in S. regalis. Sex identification was successful only in H. forskali, and sexual ratio was 1:1. It was impossible to identify gender in S. regalis, since all the individuals arrived to the Aquaculture Laboratory eviscerated, due to trawl capture method, which made impossible to assess maturation stage. However, after eight months, in 40% of individuals was possible to observe residual gonad. In H. forskali, it was possible to establish a correlation between gonads grade colorations and gametes diameters.
Discussion and Conclusion
In order to introduce these species in aquaculture production, it is necessary to have knowledge about their reproductive biology and life cycle. To know the specimens sex to maintain an appropriate ratio is essential for sexual reproduction (Tuwo and Conand, 1992). The use of a less invasive method to identify holothurian gender is essential, once the evisceration is often a symptom of stress in this animal group (Shiell and Uthicke, 2006).
The gonadal macroscopic and microscopic analysis of H. forskali, allowed the observation of different coloration grades and diameters, respectively, according to different maturity stages, corresponding the larger diameter to the most intense colour. Sexual behaviour is another tool to understand the reproductive cycle for the introduction of these new species in aquaculture practice (Keshavarz et al., 2012; Pangkey et al., 2012).
References
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