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Mariculture of sea cucumber in the Red Sea - the Egyptian experience

Howaida R. Gabr1, Ashraf I. Ahmed1, Mahmoud H. Hanafy1,2, Andrew J. Lawrence3, Mohammed I. Ahmed1 and Salah G. El-Etreby1

1Suez Canal University, Ismailia, Egypt, 2Egyptian Environmental Affairs Agency, Hurghada, Egypt, 3University of Hull, Hull, UK

Abstract

Severe overfishing of sea cucumbers has occurred in most countries of the world. Even though they were abundant along the Red Sea coast of Egypt in the mid 1990s, sea cucumber populations are now significantly reduced and some species have almost disappeared. As a consequence, and as part of a Darwin Initiative project, the release of cultured juveniles is being examined at the Marine Science Department in Suez Canal University, Egypt, as a means of restoring and, eventually, enhancing sea cucumber stocks. One of the most important sea cucumber species occurring along the Red Sea coasts is Actinopyga mauritiana. Worldwide, this species is highly valued, in great demand and is harvested in large numbers. This paper summarizes the morphological characteristics, anatomy and biology of this species as an introduction, before over viewing the spawning methods attempted in the Red Sea. The results indicate that outside the spawning season, asexual propagation methods appear the most practical option for increasing the stock of cultured individuals. However, this will only be practicable if the mortality rate of A. mauritiana can be reduced during the process and both segments are able to regenerate their gonads. If successful, there is some potential to use this technique in hatcheries with minimum costs.

Keywords: Red Sea, Actinopyga mauritiana, reproductive biology, asexual reproduction

Introduction

Increased demand for beche-de-mer and worldwide declines in stocks of tropical sea cucumbers has encouraged aquaculture, stock restoration and enhancement programs for holothurians (Conand and Byrne, 1993; Battaglene and Bell, 1999). However, reliable techniques for induced spawning in holothurians have been developed for relatively few species. The most commonly produced sea cucumber species at present are temperate sea cucumber Apostichopus japonicus and the tropical species, Holothuria scabra. The juvenile production technique for these two species has been established in China, Japan, India, Indonesia and the Solomon Islands, among other (James, 1996; Battaglene and Bell, 1999; Battaglene et al., 1999).

Worldwide, Actinopyga mauritiana is highly valued, in great demand and is harvested in large numbers. This species, widely known as surf redfish, is amongst the most widespread and important holothurians in the Egyptian Red Sea and Gulf of Aqaba. Actinopyga mauritiana is locally called “cajeno” and is generally considered a low value beche-de-mer species. However, due to overfishing of high value species worldwide (Conand and Byrne, 1993) it is likely to become more important in tropical fisheries in the near future. Adults are dried and processed for their gummy meat (muscular body wall), which is exported primarily to China PR, Hong Kong SAR (China) and Singapore. The meat is high in protein, low in fat and believed to be an aphrodisiac. Literature evidence supports the fact that A. mauritiana does indeed contain compounds of potential biological activity (Stonik and Elyakov, 1988).

Actinopyga mauritiana is very common throughout the Indo-West-Pacific region (Conand, 1993). In the Red Sea, the species is usually found in subtidal and intertidal areas. It is very abundant in sandy areas, sea grasses and sand lagoons in the coral reef. The species is distributed over a wide range of depths from the reef flat to 30 m deep, but the majority of the individuals are found in between 5-10 m deep.

Few studies have been carried on the reproductive biology of Actinopyga mauritiana (Conand, 1993; Hopper et al., 1998; Ramofafia et al., 2001). The information on its reproductive mode is important for the sustainable management of the fishery and aquaculture of this species.

While sea cucumbers can reproduce sexually, the ability to reproduce asexually by transverse fission has been known to occur in eight aspidochirotide species (Uthicke, 1997), and may be artificially induced in several others (Reichenbach et al., 1996). Fission is a seasonally occurring event in Holothuria atra (Conand and De Ridder, 1990; Chao et al., 1993; Uthicke, 1997), H. parvula (Emson and Mladenov, 1987), H. edulis and Stichopus chloronotus (Uthicke, 1997). All fissiparous species also reproduce sexually by broadcast spawning of gametes during distinct spawning seasons (Conand, 1993). However, cloning by transverse fission is an important means of maintenance of population size in several echinoderm species (Emson and Wilkie, 1980; Ottesen and Lucas, 1982) including sediment-feeding sea cucumbers of the order aspidochirotida (Chao et al., 1993; Conand, 1996; Uthicke, 1997, 1998). The goals of the present study are first, to describe gonad development in A. mauritiana in the Red Sea and second, to evaluate the potential of asexual propagation through induced transverse fission as a simple, cost-effective method for population-size maintenance.

Materials and methods

Sampling sites

To study the reproductive biology of Actinopyga mauritiana, twenty specimens were collected monthly at Al-Gemsha Bay from December 2002 to September 2003. The bay is located in the Northern sector of the Red Sea (Figure 1), about 20 km from Hurghada (27° 66’ 56” N: 33° 51’ 45” E). The area of the bay is about 40 km2 characterized by soft bottom habitat of sea grass beds dominated by Halophila stipulacea and Halodula uninervis. The depth of the bay ranges between 0.5 and 9 m, with a mean depth of 6 m. Animals were collected by SCUBA diving. Due to the dwindling animals stocks in the bay, the specimens for the asexual reproduction trial were collected from Nuwibaa on the Gulf of Aqaba (28° 43’ 35” N: 34° 37’ 22” E).

Figure 1. Map of the Egyptian section of the Red Sea showing the sampling sites of Actinopyga mauritiana.

Gonad dissection and processing

Total length was measured immediately on site to the nearest 0.5 cm to minimize the expected changes in the animal’s size during transit. In the laboratory, total weight to the nearest 0.1 g was measured for each specimen and then all the animals were dissected. Gonads were removed, sexed, weighed to the nearest 0.01 g and preserved in 7 % formalin. The body wall weight was obtained, which is more representative than the total weight. The latter includes the coelomic fluid and digestive tract contents which causes considerable variability (Conand, 1989). For each animal, the gonad index (GI) was determined as:

GI = (Wg/Wb)x100

Where Wg is the wet gonad weight and Wb is the body wall weight.

The gonads’ macro- and microscopic features were used to assess maturity stages following previous studies (Sewell, 1992; Tuwo and Conand, 1992; Ramofafia et al., 2001). These were wet gonad size, gonad colour and consistency, and presence of gametes in squash preparations. Based on these criteria, a four stage maturity scale was determined: Stage I, premature or recovery; Stage II, maturing; Stage III, mature; and Stage IV, post-spawning. Each gonad was examined and assigned to one of these stages. These four maturity stages were verified by histological examination. A sub-sample of 5 animals (representing the available size range) was taken from each monthly sample for histology. Small sections of gonad tubules were dehydrated, embedded in paraffin, sectioned (5 mm thick) and stained with haemotoxylin and eosin (H/E). Based on the staining response for H/E each gonad was assigned a gametogenic stage. The histological stages of gametogenesis were based on those used in previous studies of sea cucumber gonads (Tuwo and Conand, 1992; Ramofafia et al., 2000). Diameters of 30 oocytes from each of the different stages of vitellogenesis (pre-, mid-, and late vitellogenic stages) were also measured.

Asexual reproduction trial

This study was undertaken at a commercial private hatchery located on the Suez Canal coast. Actinopyga mauritiana were collected from Nwuibaa and transported to the hatchery in 1 000 litre lidded plastic containers. During the transportation time, the water was aerated. At the hatchery, the animals were placed in 10 m3 concrete tanks with running seawater. The bottoms of the tanks were covered with a thin layer of sand. Before starting the experiment all animals were allowed to adapt to the new habitat for one week. To determine the potential of A. mauritiana to reproduce asexually, 180 individuals were used in this trial. They were separated into two size groups, each group was held in separate tank to assess the effect of size on the ability of the individuals to reproduce asexually. The first group contains 100 individuals ranging in length from 5 to 15 cm and weighing from 50 to 200 g. The second group contained 80 individuals ranging in size from 15 to 28 cm and weighing from 220 to 570 g.

In order to force asexual division, each sea cucumber was fitted with a rubber band across the mid-body. This was found to be efficient in the case of some tropical Pacific species (Reichenbach and Holloway, 1995). After the individuals had completely divided, the anterior ends were moved to separate tanks from the posterior ends. The tanks were monitored daily and the mortality rate was recorded. The experiment was maintained for three months and terminated when the internal organs, except the gonads, of all the divided halves had regenerated. Sacrificing some animals and scanning with ultrasound were two methods used to monitor the regeneration of the internal organs. The percentage of survival was calculated for each size group as following:

Survival percentage S% = [(A+P)/2T]*100

Where (A+P) corresponded to the number of the anterior and posterior ends, respectively, and (T) to the total number of specimens that had undergone fission.

Results

Sex ratio

A total of 244 Actinopyga mauritiana were collected from Al-Gemsha Bay. Of the individuals sectioned (102 sexed and 142 unsexed), 53 individuals (52 %) were females, and 49 individual (48 %) were males. The unsexed individuals either carried unidentified gonads or had no visible gonads. The females and the males are more or less equal in proportion, giving a sex ratio of 1:1.

Maturity scale

Four stages of sexual maturity for Actinopyga mauritiana were defined according to the gross morphology and microscopic development in the gonads (Plates 1 and 2). The maturation process was similar morphologically and histologically. Table 1 summarizes the mean dimensions of the gonadal tubules and oocytes diameter at various maturity stages.

Stage I - premature or recovery.

Immature gonads could not be sexed by microscopic examination of the preparations. Sex could only be identified by histology. The tubules were white and unbranched fine thread-like tubules. Abundant pre-vitellogenic oocytes lined the germinal epithelium of the ovary (Plate 1A). Immature testes were characterized by the presence of spermatogonia and developing spermatocytes along the germinal epithelium (Plate 2A).

Stage II - Maturing

The tubules were longer, thicker and branched. Sex could be determined microscopically by the presence of developing gametes. Ovaries and testes were more whitish. Active vitellogenesis, with oocytes growing from early to later stages of vitellogenesis, was observed (Plate 1B). Growing testes developed numerous infolds of the germinal layer with columns of spermatocytes (Plate 2B).

Stage III - Mature

Tubules were bulging and their colour changed from whitish to off-white in males and orange in females. Oocytes were tightly packed and filled the entire tubule lumina (Plate 1C). Oocytes were not attached to tubule walls, which still held oogonia. At this stage, most oocytes were mature. They had a very wide, clearly visible nucleus. Mature testes were fully packed with spermatozoa. Spermatozoa appeared in the form of thick granules in the tubules lumina (Plate 2C).

Stage IV- Post-spawnimg

Tubules were flaccid and more or less empty, but a considerable part of the tubule volume was still occupied by undischarged gametes. Undischarged oocytes at various stages of deterioration were noted in females. Undergoing atresia (yellowish clusters) was observed (Plate 1D). Spawned testes still contained spermatozoa and exhibited a renewal of spermatogenesis with spermatocytes present along the germinal epithelium. Lumen became spacious and contained debris and phagocytes (Plate 2D).

Plate 1. Development for A. mauritiana: (A) Stage I, premature or recovery; (B) Stage II, maturing; (C) Stage III, mature; (D) Stage IV, post-spawning. g: gonad wall; o: ripe oocytes; ph: phagocytes; po: previtallogenic oocytes. Scale bars represent 100mm.

Plate 2. Microscopic stages of male gonad development for A. mauritiana: (A) Stage I, premature or recovery; (B) Stage II, maturing; (C) Stage III, mature; (D) Stage IV, post-spawning, g: gonad wall; ph: phagocytes; sp: spermatogenesis; s: mature spermatozoa. Scale bars represent 100mm.

Table 1. The mean size of male (M) and female (F) gonadal tubules and oocytes diameters for A. mauritiana at different stages of development.

Stage

Gonad tubules

Oocyte diameter (µm)


Length (cm)

Weight (g)

Diameter (mm)



M

F

M

F

M

F


Premature or recovery

3.00 ± 0.50

2.50 ± 0.40

0.15 ± 0.20

2.51 ± 0.70

0.23 ± 0.01

0.13 ± 0.26

19.60 ± 0.37

Maturing

3.50 ± 0.20

4.50 ± 0.30

5.20 ± 0.45

15.80 ± 0.89

0.42 ± 0.06

0.50 ± 0.04

32.90 ± 0.03

Mature

9.80 ± 0.40

12.00 ± 0.50

15.60 ± 0.98

45.00 ± 0.65

0.53 ± 0.03

0.87 ± 0.02

107.20 ± 0.43

Post-spawning

6.50 ± 0.44

7.30 ± 0.30

8.50 ± 0.84

18.35 ± 1.65

0.45 ± 0.06

0.60 ± 0.03

84.00 ± 0.91

Size at maturity

Figure 2 illustrates the relationship between the gametogenic stages (I, II, III, IV) and the length of the sea cucumber. This figure (based on 53 females and 49 males taken throughout the sampling period) indicates that the size at first maturation for female and male Actinopyga mauritiana occurs at similar sizes (23 and 22 cm for females and males, respectively).

Monthly variation in maturity stages

To determine the spawning season, the occurrence of mature females and males throughout the period of study was examined. Figures 3 and 4 illustrate the monthly percentage composition of the maturity stages of female and male Actinopyga mauritiana, respectively. Most mature females and males (Stage III) were observed between March and August. Meanwhile, the peak incidence of mature males (Stage III) coincided with the peak incidence of spawning females (March to May).

Figure 2. Size at first sexual maturity of A. mauritiana.

Figure 3. Monthly variation of gametogenic stages in female A. mauritiana.

Figure 4. Monthly variation of gametogenic stages in male A. mauritiana.

Monthly changes in gonad index

The pattern of maturation indicated by examination of the gametogenic stages (Figures 3 and 4) was supported by the gonad index (GI). The seasonal variation in the GI was pronounced for both sexes (Figure 5). The female and male gonad index increased in March and peaked in April. This coincided with the peak percentage of mature specimens. The GI declined in May and June, then a gradually increased to an intermediate level in July and August. For both sexes, the GI dropped in September. The drop of GI in May and June was due to the presence of specimens with gonad weights that varied significantly from the mean.

Figure 5. Monthly variation in means gonad index (GI) for female and male A. mauritiana

Asexual reproduction trial

Observation - It is not known whether Actinopyga mauritiana is able to reproduce asexually by transverse fission in addition to its sexual mode of reproduction. However this experiment indicates that this species has some capacity to reproduce asexually in response to stressful conditions.

Immediately after the rubber bands were placed in the mid-body of the sea cucumbers, they started to constrict slightly in the middle and showed some swelling in the posterior section (Plate 3A). After one hour, the constriction became slightly more distinct; giving a heart shape to the posterior half (Plate 3B). The anterior and posterior sections slowly rotated in opposite directions resulting in a more distinct construction (Plate 3C). The posterior half of the individual remained stationary while the anterior end continued to move forward. At this point, the body wall at the fission site started to rupture, and some white tissue started to appear in the constriction area. The two body parts remained connected by only a string of tissue for at least four more hours (Plate 3D). The entire process of fission lasted for a whole day. The body wall at the fission site remained a liquid or mucus like consistency for at least six more hours (Plate 3E). After two days, the body wall had its normal consistency and the wounds at both ends were healed and nearly entirely closed (Plate 3F).

Dissections of the posterior and anterior halves of the individual immediately after fissions revealed that most of the intestines, and the respiratory organs (water lungs) were separated equally between the two sections.

Plate 3. Photographs showing the process of induced transverse fission in A. mauritiana. a: anterior part; p: posterior part.

Survival rate

The survival rate of the small size group (average length 12 cm and average weight 130 g) was 75 % with 65 % survival of the anterior parts and 85 % survival of the posterior parts (Figure 6). The survival rate of the large size group (average length 19 cm and average weight 330 g) was 58 % with 50 % survival of the anterior parts and 66 % survival of the posterior parts (Figure 6).

Figure 6. Survival rate of asexual reproduction experiment for two size groups of A. mauritiana.

Regeneration rate

Dissection of the sea cucumber on a monthly interval indicated that large individuals of A. mauritiana (average length 19 cm and average weight 330 g) were able to regenerate the posterior and the anterior parts into a whole individual, in around 100 days. In contrast, small animals (average length 12 cm and average weight 130 g) were able to regenerate both anterior and posterior parts into whole individuals in around 60 to 80 days. The shortest regeneration time was for the posterior parts of the smallest size class.

Discussion

Reproductive cycle

This species exhibits traits typical of many aspidochirote holothurian species: annual reproductive cycle, gametogenesis occurring in synchrony among sexes, partial spawning and total gonad resorption after spawning.

Size at first maturity was very similar for both sexes. The restricted spawning season for this species (spring and early summer) and the slight variation in temperature during this time (22-25 °C) will give rise to a cohort with minimal growth rate differences between individuals.

The size of gonadal tubules and oocytes diameters were correlated to gametogenesis and corresponded well to the descriptive maturity stages assigned to this species. This supports previous work on the same species in which the size of gonadal tubules was recommended as adequately reflecting the maturation process (Ramofafia et al., 2001).

The data on gonad index, tubule morphology and gonad histology indicate that Actinopyga mauritiana has an annual reproductive cycle in the Red Sea and that gametogenesis occurs in synchrony in both sexes. In general, the period of peak reproductive activity is between spring and summer. An annual reproductive cycle with a summer spawning season has also been recorded for this species in Solomon Islands (Ramofafia et al., 2001), New Caledonia and Guam (Conand, 1993; Hopper et al., 1998).

Spawning in Actinopyga mauritiana is partial with mature and spawned tubules evident in dissected specimens during the breeding season. Furthermore, histology revealed that not all gametes were released from spawned tubules and that re-initiation of gametogenesis occurred in these tubules. It is not known whether unspawned tubules will eventually release their gametes. Partial spawning has been documented for the same species (Ramofafia et al., 2001) and for Holothuria fuscogilva (Ramofafia et al., 2000) in the Solomon Islands and has also been observed in other holothurians (Sewell, 1992; Hamel et al., 1993).

This study showed that there was a period during the reproductive cycle in which the gonads were absent. This suggests that total resorption of the gonads may happen. The resorption of gonad in spawned individuals again supports the observations in previous studies on the same species (Ramofafia et al., 2001) and as also observed in H. fuscogilva (Ramofafia et al., 2000).

Asexual reproduction

Most holothurian species which have adopted asexual reproduction follow the “twisting-and-stretching” mode of fission (Emson and Wilkie, 1980): the anterior and posterior sections slowly rotate in opposite directions, resulting in a constriction of the body. This process had not been previously observed in Actinopyga mauritiana. Rubber bands placed mid-body of the individuals may provide an effective yet simple technique to induce transverse fission. Asexual reproduction in A. mauritiana did follow the twisting-and-stretching mode, as described for species of the genus Holothuria (Emson and Wilkie, 1980), which may take up to several hours. The mechanical properties of the body wall of many holothurians are well described for S. chloronotus (Motokawa, 1982, 1984). Connective tissue in holothurians (and other echinoderms) is named “catch-connective-tissue” (Motokawa, 1984) or “mutable collagenous tissue” (Wilkie, 1984). These tissues may contract or expand nearly instantaneously without the action of muscles, probably under the control of the nervous system (Wilkie, 1984). Actinopyga mauritiana appears to be another good example of a species with these properties. It appears that in addition to asexual reproduction, another important function of the catch connective tissue is to aide rapid wound healing.

The overall trend in the fission study was that higher survival rates were seen in the smaller size group and that the posterior ends had better survival and regeneration rates than the anterior ends. This was observed previously in other holothurians (Reichenbach et al., 1996). The ability of the posterior parts to obtain oxygen needed for more energy may be a crucial factor in the process. This may be supported by the presence of the origin of the respiratory trees in the posterior part. On the contrary, the anterior part will obtain its oxygen through diffusion across the body until the respiratory trees are regenerated.

Out of the spawning season, asexual reproduction appears as the most practical option for increasing the stock of A. mauritiana. This study indicates that the survival and regeneration rate in small size individuals is higher (75 % survival and 60 days to regenerate) when compared with the larger individuals (58 % survival and 100 days to regenerate). Uthicke (2001) suggested that the body size of sea cucumber could have an effect on the likelihood of asexual reproduction taking place. This also agrees with previous studies on temperate water species, in which a sea cucumber takes from 30 to 120 days to regenerate (Byrne, 1985).

This possible application of asexual propagation of A. mauritiana would have to be carefully considered. At the simplest level, it may offer a good means of increasing the broodstock of cultured animals, thereby reducing the pressure on the natural environment. However, this will only be applicable if both the anterior and posterior sections are able to regenerate reproductive organs. These have not been observed in the current study.

Conclusions

Actinopyga mauritiana is commercially important for the production of beche-de-mer, a dried body wall product. Depletion of wild stocks and interest in aquaculture of this species prompted the current investigation of aspects of their biology essential for artificial culture. A. mauritiana has an annual reproductive cycle. Gametes are spawned from early spring through to summer with increased spawning activity in spring. Spawning coincided with the spring plankton bloom in the Red Sea, increasing day length and seawater temperature. This suggests that food supply, photoperiod and temperature should be tested as triggers for artificial spawning of broodstock in culture. Although, in nature asexual reproduction has not been observed in A. mauritiana, it is induced readily in the laboratory. The overall trend was that the survival rate increased in smaller individuals. The implications of this for the management of A. mauritiana populations and the fishery will require careful consideration. In the first instance, further research is required on the possible influence of fission on sexual reproductive activities and genetic alterations of culture and wild populations.

Acknowledgment

We would like to thank the staff of Egyptian Environmental Affairs Agencies (EEAA) and Marine Science Department for their assistance. The research was funded by the UK Darwin Initiative.

References

Battaglene, S.C. & Bell, J.D. 1999. Potential of the tropical Indo-Pacific sea cucumber, Holothuria scabra, for stock enhancement. In: Stock Enhancement and Sea Ranching. Howell, B.R., Mokness, E., Svasand, T. (Eds.). pp. 478-490. Proceedings First International Symposium on Stock Enhancement and Sea Ranching, 8-11 September 1997, Bergen, Norway. Blackwell, Oxford.

Battaglene, S.C., Seymour, E.J. & Ramofafia, C. 1999. Survival and growth of cultured juvenile sea cucumbers Holothuria scabra. Aquaculture, 178:293-322.

Byrne, M. 1985. Evisceration behaviour and the sesonal incidence of evscration in the Holothurian Eupentacta quinquestemita (Selenka). Ophelia, 24:75-90.

Chao, S.M, Chen, C.P. & Alexander, P.S. 1993. Fission and its effect on population structure of Holothuria atra (Echinodermata: Holothuroidea) in Taiwan. Marine Biology, 116:109-115.

Conand, C. 1993. Reproductive biology of the holothurians from the major communities for the New Caledonia lagoon. Marine Biology, 116:439-450.

Conand, C. 1996. Asexual reproduction by fission in Holothuria atra. Variability of some parameters in populations from the tropical Indo-Pacific. Oceanol Acta., 19:209-216.

Conand, C. & Byrne, M. 1993. A review of recent developments in the world sea cucumber fisheries. Marine Fisheries Review, 55:1-13.

Conand, C. & De Ridder, C. 1990. Reproduction asexuee per scission chez Holothuria atra (Holothuroidea) dans des populations de platiers recifamx. In: Echinoderm researech. de Rideer, C., Dubois, P., Jangoux, M., Lehaye, M.C. (Eds.). p.71-76. Balkema, Rotterdam.

Emson, R.H. & Maldenov, P.V. 1987. Studies of the fissiparous holothurian Holothuria parvula (Selenka) (Echinodermata: Holothuroidea). Journal of Expermintal Marine Ecology, 111:195-211.

Emson, R.H. & Wilkie, I.C. 1980. Fission and autotomy in echinoderms. Oceanography Marine Biology A. Review, 18:155-250.

Hamel, J.-F., Himmelman, J.H. & Dufresne, L. 1993. Gametogensis and spawning of the sea cucumber Psolus fabricii (Duben and Koren). Biological Bulletin. Marine Biological laboratory, Woods Hole, 184:25-143.

Hopper, D.R., Hunter, C.L. & Richmond, R.H. 1998. Sexual reproduction of the tropical sea cucumber Actinopyga mauritiana in Guam. Bulliten of Marine Scinece, 63:1-10.

James, D.B. 1996. Culture of sea-cucumber. CMFRI Bulletin, 48:120-126.

Krishnaswamy, S. & Krishnan, S. 1967. Report on the reproductive cycle of the holothurian Holothuria scabra Jaeger. Curr. Science, 36:155-156.

Motokawa, T. 1982. Rapid change in mechanical properites of Echinoderm connective tissues coused by coelomic fluid. Comp.Biochemical.Pysiology, 70(1):41-8.

Motokawa, T. 1984. Connective tissue catch in echinoderms. Biol. Rev., 59:255-270.

Ottesen, P.O. & Lucas, J.S. 1982. Divide or broadcast: interrelation of asexual and sexual reproduction in a population of the fissiparous zhermaphroditic seastar Nepanthia belcheri (Asteroidea: Asterinidae). Marine Biology, 69:223-233.

Ramofafia, C., Battaglene, S.C., Bell, J.D. & Byrne, M. 2000. Reproductive biology of the commercial sea cucumber Holothuria fuscogilva in Solmon Islands. Marine Biology, 136:1045-1056.

Ramofafia, C., Byrne, M. & Battaglene, S.C. 2001. Reproductive biology of Actinopyga mauritiana in the Solomon Islands. Journal of Marine Biology Association. U.K., 81:523-531.

Reichenbach,Y. & Hollway, S. 1995. Potential of asexual propagation of several commercially important species of tropical sea cucumbers (Echinodermata). Journal of the World Aquaculture Society, 26:272-278.

Reichenbach, Y., Nishar, & A. Saeed. 1996. Species and size-related in asexual propagation of commercially important species of tropoical sea cucumbers. Journal of the World Aquaculture Society, 27:475-482.

Sewell, M.A. 1992. Reproduction of the temperate aspidochirote Stichopus mollis (Echinodermata: Holothuroidea) in New Zealand. Ophelia, 3 5:103 -121.

Stonik, V.A. & Elyakov, G.B. 1988. Secondary Metabolits from Echinoderms as Chemotaxonomic Markers. In: Bioorganic Marine Chemistry, V2. p.43-82. Springer-Verlage, Berlin, Heidelberg.

Tuwo, A. & Conand, C. 1992. Reproductive biology of the holothurian Holothuria forskali (Echinodermata). Journal of Marine Biology Association. UK., 72:745-758.

Uthicke, S. 1997. Seasonality of asexual reproduction in Holothuria atra, Holothuria edulis and Stichopus chloronotus (Holothuroidea: Aspidochirotida) on the Great Barrier Reef. Marine Biology, 129:435-441.

Uthicke, S. 1998. Regeneration of Holothuria atra Holothuria edulis and Stichopus chloronotus: intact individuals and products of asexual reproduction. In: Echinoderms. Mooi R. & Telford, M. (Eds.). pp.531-536. San Francisco Proceedings of the Ninth International Echinoderm Conference. Balkema, Rotterdam.

Uthicke, S. 2001. Influence of asexual reproduction on the structure and dynamics of Holothuria (Halodeima) atra and Stichopus chloronotus populations of the Great Barrier Reef. Marine and Freshwater Research, 52:205-215.

Wiliki, I.C. 1984. Variable tensility in echinoderm collagenous tissues: A review. Marine Behaviour and Physiology, 11:1-34.


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