Introduction
Various studies have demonstrated the interest of including deposit feeders, as an integrated element of IMTA systems devoted to the consumption of organic materials (Cubillo et al., 2016). Sea cucumbers are of interest as deposit feeder, for their environmental value, their interesting growth potential and low mortality rates (Zamora and Jeffs, 2012). Various sea cucumber species within IMTA systems have been tested for co-culture with a variety of fish (Hannah et al., 2013), molluscs (Kang et al., 2003; Zhou, 2006) and seaweed (Beltran‐Gutierrez et al., 2016). The interest of Holothurians as deposit feeders was demonstrated in these studies and their mitigation ability within different IMTA systems was further tested, indicating that sea cucumbers can optimise the net use of wastes (Reid et al., 2013).
Given the existing research, the current study investigates the potential for the integrated culture of the sea cucumber H. sanctori with the abalone Haliotis tuberculata coccinea in order to develop the integrated Land Based IMTA production of these species.
Materials and methods
Experimental specimens
Young individuals of H. sanctori (mean weight: 31.07 ± 14.51 g) were collected at a depth of 0-10 m, by scuba diving, and maintained and acclimated in experimental installations, placing them under abalone (H. tuberculata coccinea) baskets (in which abalone were fed macroalgae). After their indoor acclimation, they were then respectively allocated to experimental IMTA units.
Adult abalone of H. tuberculata coccinea (mean weight: 37.32 ± 9.01g and mean size: 60.83 ± 5.30mm) were obtained from the abalone production unit of the ECOAQUA institute, University of Las Palmas de Gran Canaria.
IMTA experimental set up
Experimental IMTA systems were designed to provide two levels compartments; one for the fed abalone (H. tuberculata coccinea) of 50L capacity and the other for sea cucumber (H. sanctori) located below the abalone compartment. Together located in 300L tank capacity. The abalone compartment was perforated on the bottom and on the sides to allow water exchange and release of abalone wastes to reach the sea cucumber located below.
Stocking density
Tests were performed in triplicates in the IMTA experimental units at two sea cucumber densities (2.5 Specimen.m-2 and 3.75 Specimen.m-2) that were placed under abalone baskets stocked at 50 Specimen/m-2 and weekly fed 0.8kg of IMTA produced macroalgae.
Growth performance and ingestion rate
Weight Gain (WG), and Specific Growth Rate (SGR) were estimated on a monthly basis while ingestion rate was estimated in mg/g/h
Biochemical analysis
Triplicate samples of sea cucumber body wall were collected from experimental and wild specimens and were analyzed for total lipids, protein, carbohydrate, and ash.
Results
Growth performance
Overall, the mean SGR and WG values differed significantly (p < 0.05) among high density and low-density treatments. All sea cucumber specimens within the density 3.75 sp.m-2, were found to lose weights and exhibit negative SGR and WG values. On the contrary, for specimens stocked at a density of 2.5 sp.m-2, their growth performance improved as all specimens could gain weight and exhibit positive SGR and WG values.
Biochemical analysis
No significant difference (p > 0.05) was observed between the proximate biochemical composition of sea cucumbers produced in the tested IMTA system and the wild-caught specimens, supporting the suitability of such system for the production of this sea cucumber species.
Discussion
The loss of condition amongst sea cucumber fed abalone faeces at high density in the current experiment indicates that stocking density has a significant impact on H. sanctori growth. Similarly, several authors have reported an inverse proportionality between sea cucumber stocking density and their growth rates (Dong et al., 2010; Pei et al., 2012). Based on these results, a stocking density of 2.5 sp.m-2 is suggested to sustain growth of H. sanctori. In terms of biochemical composition, the similarities observed between the experimental specimens and their wild counterparts suggest the ability of sea cucumbers to adjust their feed intake to satisfy their nutritional requirements and to maintain a steady nutrient composition within their body walls, this being of interest for future successful production of the species.
References
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Acknowledgements
This research is supported by the EU H2020 research and innovation program within the collaborative project “AQUAVITAE– New species, processes and products contributing to increased production and improved sustainability in emerging low trophic, and existing low and high trophic aquaculture value chains in the Atlantic” (https://aquavitaeproject.eu/) under Grant Agreement No. 818173.