The first attempts made towards the domestication of sea cucumbers in Kenya

The potential for culture of sandfish Holothuria scabra in Kenya was investigated based on a sample of 1000 wild individuals with an average weight of 40-80 g. This experiment was conducted to identify suitable methods of collection, transportation, acclimatization, and growth at different stocking densities. Packing methods tested during collection were oxygen filled plastic bags and open basins. For method 1, Sample 1 sandfishes were carried individually in oxygen filled plastic bags with sea water. Sample 2 included a total of five sandfishes per bag, and Sample 3 had a maximum of ten sandfishes. Under method 2 specimens were transported using open basins containing sand and aerated sea water in densities of 10, 20 and 30 individuals per basin. The mean (±SD) percentage evisceration rate during transportation in method 1 was 0 for a density of 1, 3.33 ± 5.77 % for a density of 5, and 20 ± 10 % for a density of 10. In method 2 evisceration occurred at all the three densities; 23.3 ± 15.28 % for the low density, 23.33 ± 2.8 % for the middle density and 36.6 ± 3.33 % for the higher density. The findings of this study provide information to contribute to the development of marine aquaculture of sea cucumber in Kenya.

SCUBA equipment (Conand and Muthiga, 2007). The processed sea cucumbers are purchased by dealers at the landing beaches who in turn sell the products to exporters based in the county capital of Mombasa who then export to Hong Kong. The major landing beaches for H. scabra are on the southern coast of Kenya in Vanga, Shimoni and Majoreni.
Studies have shown that over 50 species of tropical sea cucumbers have been commercially exploited and traded including H. scabra, the most valuable sea cucumber species exploited in tropical areas (Purcell, 2010;Purcell et al., 2012). Other holothurians facing high exploitation are H. fuscogilva and H. nobilis, which are also found in Kenyan waters and are highly valued (Conand and Muthiga, 2007). Overexploitation in the sea cucumber fishery has created a worldwide management concern with the main reasons being worldwide demand, high value, serial local depletions, and fishermen migration to new fishing areas (Lovatelli et al., 2004). A study by Uthicke (2004) states that the slow nature of sea cucumber population recovery after depletion has led to a situation that has compromised sustainability. Further research by Hasan (2005) and Friedman et al. (2011) found that a heavily exploited sea cucumber population could take more than 50 years to recover. In addition, low H. scabra densities may decrease chances of successful spawning thus impeding population recovery and increasing the risk of an Allee effect (Bell et al., 2008).
From the aforementioned discussion it is clear that sea cucumber have been under intense fishing pressure, warranting need for effective conservation measures. The organisms provide an important contribution to livelihoods of coastal communities which has fostered the need for domestication to ascertain viability of culture and farming options. Further, cultivation of H. scabra has increasingly become necessary to support stock enhancement programmes (Giraspy and Ivy, 2005) and to meet the export market demand (Purcell et al., 2012). Domestication will protect the organisms from identified threats such as habitat destruction and unsustainable fishing until the sea cucumbers reach marketable size or a minimum size for restocking. Hatchery production of H. scabra has been carried out in different countries across the globe (Kumara and Dissanayake, 2017). Other countries have initiated restocking and sea ranching (Purcell et al., 2012;Eriksson et al., 2014;Watanabe et al., 2014). In China, H. scabra aquaculture has achieved milestones where 5 g juveniles have been produced and cultured to commercial harvestable adults of 300 to 500 g weight (Purcell and Wu, 2017). Studies have shown that success of H. scabra aquaculture is limited to hatchery production with reliance on viable broodstock collected from wild populations ( James, 2012).
Hatchery production of H. scabra juveniles relies on control of broodstock collection, maintenance, spawning, fertilization, larval rearing, and post larvae settlement rearing (Hamel et al., 2022). For domestication purposes, transportation of wild collected individuals is essential and it follows different procedures which vary from one hatchery to another (Hamel et al., 2022). Studies by Battaglene (1999) mentioned that sea cucumber collection needs to be done under minimal salinity and temperature variations to avoid evisceration during transport. In other studies, individuals have been placed individually in oxygen filled bags with seawater (Ito, 2014;Abidin et al., 2016;Kumara and Dissanayake, 2017). Studies by Tuwo et al (2019) assessed the evisceration rate of H. scabra using closed and open transportation modes and their findings showed that evisceration was triggered by the presence of decaying individuals in the transportation bags that had eviscerated before transport. Acclimatization in pre-prepared holding tanks aids in the quick recovery of H. scabra individuals that survive during transportation (Hamel et al., 2022).
In Kenya, there has been no culture trials of H. scabra so far. The aim of this study was therefore twofold; to identify a suitable method of sea cucumber transportation, and to understand and establish optimal acclimatization conditions at different densities. This article documents the first attempts made towards domestication of sea cucumber in Kenya as initial steps towards H. scabra culture for natural stock enhancement and as an opportunity for an alternative livelihood for the fisher communities.

Experimental design
The study tested conditions for sea cucumber transportation and acclimatization. Two transportation modes were investigated including varying packing methods and sandfish density. Plastic aerated bags were used for Method 1 (closed model) and aerated open basins for Method 2 (open model). The treatment had three replicates for both methods. Potential evisceration using both methods was monitored while transporting the sea cucumbers. Water quality parameters including salinity, temperature, dissolved oxygen, pH, total dissolved solids (TDS) and conductivity were monitored before transport, during transport and also within the culture facility by using a multi-parameter meter kit (Hanna Instruments). After acclimatization, a three-month study was designed using a portion of the sea cucumbers that survived during transportation to determine growth performance at three different stocking densities (5, 10, and 15 individuals) with replicates in flow through culture tanks.

Culture site and systems
The marine hatchery at Kenya Marine and Fisheries Research Institute (KMFRI) located 5 km from Mombasa town (GPS 4.0552°S and 39.6821°E) was used as the experimental site to conduct the H. scabra hatchery trials. A concrete outdoor tank measuring 5m x 3m x 1m was used as a holding facility for the H. scabra specimens collected from the wild. The bottom of the tank was covered with 15 cm of sand to provide the sandfishes with an environment that simulated their natural habitat. This provided a burrowing medium to allow for their usual behavioral patterns as well as to provide a source of food and shelter from adverse environmental conditions and sometimes predation (Wiedemeyer, 1992;Mercier et al., 2000). The holding tank was continuously supplied with seawater extracted from a borehole with a salinity of 27 ppt and a temperature of 25 °C. An air blower maintained continuous aeration to the water as the sandfish acclimatized for a period of two weeks before subjecting them to different experimental treatments.

Collection of specimens
During this study a total of 1000 individuals with an average weight of 40 g to 80 g were collected in

Handling of collected organisms
The sampling points were chosen based on ease of accessibility and availability of the organisms within the sandy seagrass beds. Upon arrival and after retrieving the sandfishes, the water quality parameters of the sea water that was used to hold the organisms were measured including salinity, temperature, dissolved oxygen, pH, TDS and conductivity. These were taken at 1:00 am using a multi-parameter kit followed up by counting and packing the organisms for transportation. The animals were carefully handled to avoid evisceration, then they were cleaned by washing their body with seawater in preparation for transportation using the two test methods. A battery pump (E-jet BP-3) was used to aerate the water in the basins during transportation. Table 1 shows the treatment detail of sandfish during transportation.
Duy (2011). Mortality in the acclimatization tank was recorded every day.

Monitoring of sea cucumber growth at three different stocking densities
After acclimatization, the growth rate of test organisms was observed for three months in different stocking densities of 5, 10 and 15. Total Length (TL) and total weight measurements were recorded after every two weeks using a string and meter ruler and an analytical weighing balance with the precision of 0.01 g to obtain length and weight gain in grams. The Specific Growth Rate (SGR) of the three stocking densities was calculated as described by (Novoa et al., 1990) as follows: Specific growth rate (SGR) = Log e (final weight)-log e (initial weight) × 100%

Data analysis
Comparisons of the different treatments for trans-

Results
Evisceration rate of the sandfish for the different methods and different densities is shown in Table 2.
The mean (±SD) percentage evisceration rate of the collected stocks of H. scabra in Method 1 was 3.33 ±5.77 % for the density of 5, and 20 ± 10 % for the density of 10 as shown in Table 3. Density 1 had no evisceration. In Method 2 evisceration occurred at all the three densities; 23.3 ±15.28 % for the low density of 10 individuals, 23.33± 2.8 % for the middle density of 20 individuals, and 36.6 ± 3.33 % for the higher density of   Twenty sea cucumbers died on the fourth and sixth day during the first three weeks of acclimatization.
Water quality parameters collected before transport, during transport and in the culture facility are presented in Table 5. Temperature, pH, salinity, transparency, and dissolved oxygen did not show marked variations between the treatments during transportation and acclimatization.
The stocking density treatments showed a 100 % survival of the test organisms. The final mean weight of sea cucumbers stocked at a density of 5 in plastic tanks was the highest at 88.96 ± 4.09 g compared to the stocking density of 10 and 15 which had a final mean weight of 60.93 ± 21.11 g and 46.91± 1.11 g respectively. The weight gain of sea cucumbers stocked in different stocking densities of 5, 10, and 15 decreased with an increase in stocking density (Table 6; Fig. 2). The specific growth rate of sea cucumbers stocked at a density of 5 was 1.03± 0.56 g followed by 0.22± 0.41 g for the stocking density of 10 and -0.37 ± 0.02 g for the stocking density of 15 sea cucumbers (Fig. 3). The test organisms showed a high acceptance of the mangrove mud as a feed as compared to the seaweed and pellet mixture.

Discussion
During this study transportation took place at night to avoid high temperature fluctuations. The sandfish that were transported in open basins were higher in density and most likely the shock and friction from the walls of the transporting basins could have exposed the sandfishes to greater stress during the four-hour transport time as compared to those that were packaged in lower densities in oxygenated polythene bags.
The study indicated that with the 40-60 % ratio of oxygen to water used, 0 evisceration, 3 % and 20 % evisceration occurred at the low, middle, and high sandfish densities in Method 1. In Method 2, an evisceration rate of 23 %, 23 %, and 36 % was experienced with the low, middle, and high densities. From this analysis the middle density seems to be most appropriate for transportation from a cost effort benefit perspective.
Oxygenation is therefore essential for long distance transportation as results show low evisceration rates in samples that had oxygen provision (Ito, 2014;Tuwo et al., 2019). The physico-chemical parameters monitored during the acclimatization period (Table 5) were within the optimum range required for sea cucumber rearing (Agudo, 2006). Wild collected holothurian species have been observed to eviscerate as a reflex response to danger, adverse environmental conditions and handling stress that makes them release their internal organs to the surrounding environment (Battaglene et al., 2002).
In this study, most organisms were found to be in good condition since most did not eviscerate. However, viscera were always removed from the water once noticed during transport in order to maintain good water quality and the well-being of the sea cucumbers. Studies have shown that H. scabra are relatively hardy organisms that can tolerate low dissolved oxygen levels (Agudo, 2006).

Stocking Density
However, provision of aeration is essential during long distance transportation in order to overcome the stress encountered during fishing, manipulation at packaging and while transporting.
Holothuroids including H. scabra are deposit feeders and studies have shown that they normally take the available food from their surrounding by ingesting deposited materials on the surface of the substrate (Roberts et al., 2000). In this study the feeds were introduced to the tank in areas where the sandfishes were observed to aggregate. Active feeding was not observed during the day. The organisms consumed the feeds on the sand substrate mostly at night when they are believed to be most active (Hamel et al., 2022). The feeds given were observed to reduce in quantity and topping up was done in small portions while taking care of the water quality in the culture facilities.
The current study revealed that sea cucumber survival was not dependent on stocking density after all treatments recorded 100 % survival. Stocking density was seen to be a factor in sea cucumber growth rate (Battaglene et al., 1999, Pitt and Duy, 2004, Lavitra et al., 2010. High growth rate was observed in treatments with low stocking density and the lowest in the high stocking density treatments. Competition for resources and space could have attributed to the varied growth rates observed (Davies et al., 2011, Slater andCarton, 2009). Improved growth rates of sea cucumber in low stocking density as seen in the present study were also observed in other studies on H. scabra (Battaglene et al., 1999;Beltran-Gutierrez et al., 2014).
The average daily growth rate of the 5 stocking density treatment in the current study was seen to range from 0.47-1.59 g which appeared to align with the results of