Growth performance and survival of Holothuria theeli (holothurian) fed with feces of Tripneustes depressus (echinoid): A multi-trophic aquaculture approach

Abstract

Integrate Multi-Trophic Aquaculture (IMTA) for deposit-feeding sea cucumbers and herbivorous sea urchin is currently a booming industry worldwide, including South America. Hence, it requires novel biotechnological protocols for culturing juvenile sea urchins and sea cucumbers with a high quality of natural food that meet organisms' nutritional needs. This study evaluated the effect on the growth performance (Specific Growth Rate, Feed Conversion Ratio, Feces Production) and survival of the sea urchin Tripneustes depressus (producer of feces) and the sea cucumber Holothuria theeli (consumer sea urchinʼs feces). Two independent experiments were conducted. For T. depressus, experiment #1: diet of seaweeds (D1: Padina durvillaei, D2: Sargassum ecuadoreanum, D3: Kappaphycus alvarezii, D4: mix of three seaweeds) and size categories (small, S: 15.0 ± 1.1 mm test diameter, TD and large, L: 25.0 ± 1.1 mm TD) were considered. For H. theeli, experiment #2: feces of diets of experiment #1 and sediment (with, without sediment) were considered. Experiment #1, SGR: small and large sea urchins fed P. durvillaei grew and gained weight faster, respectively (S: 3.0 ± 0.05 cm TD, 7.9 ± 0.2 g; L: 2.1 ± 0.1 cm TD, 5.3 ± 0.1 g). Sea urchins fed P. durvillaei and those of small size had lower FCR (diet: 7.2 ± 0.6 g; size: 13.1 ± 2.4 g, P < .05) and large and small sea urchins fed P. durvillaei (L: 31.1 ± 2.7 g d−1; S: 11.1 ± 1.2 g d−1) and mixture of seaweeds produced higher amount of feces per day, respectively (L: 28.9 ± 1.9 g d−1; S: 10.9 ± 1.2 g d−1, P < .05). Experiment #2, sea cucumbers fed diets plus sediment grew and gained weight faster (1.69 ± 0.31 cm, 4.1 ± 0.4 g, P < .05) than those diets without sediment (0.96 ± 0.25 cm, 3.3 ± 0.4 g). Sea urchins kept in the starved condition massively died at day 80, but sea cucumbers in the starved condition without sediment reduced their length and weight, by 85%, but did not die. This study highlighted the importance of feces of T. depressus on the growth of the sea cucumber H. theeli. This is a perfectible protocol for production of juveniles of T. depressus and H. theeli at IMTAs in Ecuador.