Abigail John Onomu

Nutrient-rich solid waste and effluent water from aquaculture remain a major problem for aquaculture in terms of environmental impact. Integrated multitrophic aquaculture (IMTA), where lower trophic level species consume the waste of fed animals, has been proposed as an alternative for sustainable aquaculture. The use of deposit-feeding sea cucumbers as extractive species in IMTA has attracted research and commercial interest in recent times, due to their low trophic level, high commercial value as food for humans, and ability to ingest sediment containing organic matter, bacteria, protozoa, diatoms, and detritus. Still, the suitability of using faecal waste from fed aquaculture animals as a potential feed requires further studies to ensure not only palatability but also nutritional value, health, and immune responses of the cultured organism. This review discusses various performance indices, such as palatability, ingestion rate, assimilation rate, faecal production rate, feed conversion ratio, growth, and survival of sea cucumber species fed various faecal wastes from different aquaculture animal sources. It further discusses various IMTA applications of sea cucumbers with selected animals. The compatibility, viability and efficacy of sea cucumbers and some aquatic animals in IMTA are summarised.

Providing optimum energy levels in diets for sea cucumbers is essential, as an excess or inadequate energy level can lead to a reduced growth rate. This study investigated the effect of diets on the growth and energy budget of juvenile sea cucumber Neostichopus grammatus for twelve weeks. The diets are abalone waste (AB); abalone waste mixed with powdered Ulva lacinulata (A + U) and Gracilaria gracilis ; abalone (A + G), formulated pellet with the inclusion of sand (P + S) and without sand (P – S). Ingestion rate was influenced by diets, such that diets, containing abalone waste (AB, A + G and A + U), exhibited higher ingestion rates ( p < 0.05) and consequently higher faecal production rates than that fed pellet (P – S and P + S). The diets affected the energy consumed from food assimilation ( C ), energy lost in faeces ( F ) and energy lost through ammonia excretion ( U ). However, the diets did not influence the energy available for growth ( G ), and the energy lost through respiration ( R ). 81–96% of energy intake was lost to R. The diets had no significant effect on G, as sea cucumbers in the various treatments all had a low and negative proportion of energy allocated to growth regardless of the feed ingested. This study has shown that the sea cucumber N. grammatus spends 81–96% of its ingested energy on respiration, leading to a deficit of energy available for growth. HIGHLIGHTS Diets affected the energy lost through ammonia excretion. Diets used in this study did not influence the energy available for growth, and the energy lost through respiration 81%–96% of energy intake than expected was lost to respiration Sand substrate in tanks is essential for the land‐based rearing of N. grammatus

The integrated multitrophic aquaculture (IMTA) of sea cucumber and abalone has been proposed as a potential bioremediation tool that stimulates increased abalone growth. This study assessed the role of sea cucumber stocking density and frequency of tank cleaning in IMTA on growth, water, and sludge bioremediation. The study was conducted for 16 weeks and was made of four treatments and four replicates; abalone cocultured with sea cucumber (low density—27: 1 g [abalone (ab): sea cucumber (sc)]) with tanks cleaned once a week (L1); abalone cocultured with sea cucumber (low density) with tanks cleaned twice a week (L2); abalone cocultured with sea cucumber (high density—15:1 g [ab:sc]) with tanks cleaned once a week (H1) and abalone cocultured with sea cucumber (high density) with tanks cleaned twice a week (H2). Rearing water nitrite was significantly lower (p = 0.001) at high stocking density of sea cucumbers, but sludge was unaffected. Tanks cleaned once weekly had higher sludge organic matter (p = 0.015) and sludge sulfur content (p = 0.020) and lower sludge carbon (p = 0.003) and nitrogen content (p = 0.049). At the end of the experiment, the stocking density of sea cucumber and frequency of tank cleaning affected abalone mean weight [p = 0.047; p = 0.011, respectively] without a significant interaction (p = 0.517). Abalone in H1 had a higher mean weight and shell length than abalone in L2 and H2 but was similar to those in L1. The stocking density and frequency of cleaning used in this study had no effect on the growth of sea cucumbers [p = 0.150; p = 0.470, respectively]. This study has shown that in an abalone–sea cucumber IMTA system, the stocking density of sea cucumber and the frequency at which tanks are cleaned influence abalone growth and bioremediation of the rearing water. Our result suggests H1 as the best density (ab:sc) and cleaning frequency. The tank cleaning frequency alone affects the tank sludge quality; tanks need not be washed too frequently as, in addition to causing animal stress, cleaning markedly increased carbon and nitrogen level of tank sludge. Both these effects are likely to negatively impact abalone growth.

Ensuring sustainability has increasingly become a significant concern not only in aquaculture but in the general agrifood sector. Therefore, it is imperative to investigate pathways to feed substitutes/best practices to enhance aquaculture sustainability. The application of fungi in aquaculture provides innovative methods to enhance the sustainability and productivity of aquaculture. Fungi play numerous roles in aquaculture, including growth, immunity enhancement and disease resistance. They also play a role in bioremediation of waste and bioflocculation. The application of fungi improves the suitability and utilization of terrestrial plant ingredients in aquaculture by reducing the fibre fractions and anti-nutritional factors and increasing the nutrients and mineral contents of plant ingredients. Fungi are good flotation agents and can enhance the buoyancy of aquafeed. Pigments from fungi enhance the colouration of fish fillets, making them more attractive to consumers. This paper, via the relevant literature, explores the multifaceted roles of fungi in aquaculture, emphasizing their potential to transform aquaculture through environmentally friendly and sustainable techniques. The effectiveness of fungi in reducing fibre fractions and enhancing nutrient availability is influenced by the duration of fermentation and the dosage administered, which may differ for various feed ingredients, making it difficult for most aquaculture farmers to apply fungi approximately. Therefore, the most effective dosage and fermentation duration for each feed ingredient should be investigated.

Water temperature and the presence of sand substrate are considered critical environmental factors affecting the growth of cultured sea cucumbers. This study investigated the effects of water temperatures and the presence or absence of sand substrate in tanks on the growth of N. grammatus fed an equal ration of abalone waste for eight weeks. Sea cucumbers with a mean weight of 8.34 g were used for the study. The treatments used in the study were Ambient water temperature + sand (A + S), Ambient water temperature without sand (A‐S), Cold water temperature + sand (C + S), and Cold‐water temperature without sand (C–S). The cold/constant water temperature was 16°C and was representative of winter conditions while the ambient/fluctuating water temperature fluctuated between 16.4 and 18.7 °C and was representative of spring conditions. At the end of the study, the sea cucumbers in A + S and C + S treatment groups exhibited an overall weight increase of 21.08% and 6.18%, respectively. The sea cucumbers reared in ambient water temperature exhibited significantly higher mean weight than those reared in cold water ( F _{1, 66} = 5.69; p = 0.02), and sea cucumbers reared with sand substrate had significantly higher mean weight compared to those without sand substrate ( F _1,66 = 19.06; p = N. grammatus in tanks were higher in ambient temperatures and that stress was reduced in the presence of sand, a habitat that mimics its natural environment. This implies that sand substrate may be necessary for the farming of N. grammatus .

Aquaculture serves as a source of protein and livelihood and is an alternative to capture fisheries, thereby reducing pressure on the wild. However, aquaculture tends to be limited by sustainability issues, which include overdependency on fishmeal, the high cost associated with fishmeal, the environmental impact of aquaculture activities, which may be detrimental to aquatic lives and the environment, and the use of antibiotics to treat diseases, which may have an adverse effect in their host or the environment. Efforts are being made toward attaining practical ways to enhance aquaculture sustainability. One such effort is using functional feed additives in feed formulation. Functional feed additives are dietary ingredients incorporated in feed formulations, not only for the usual provision of basic nutritional requirements as offered by traditional feed but also for growth and health enhancement; environmental and economic gain. This review emphasizes the importance of incorporating functional feed additives such as probiotics, prebiotics, symbiotics, and phytogenics. This study evaluates and presents holistic information on functional additives, their roles in enhancing aquaculture sustainability, and the challenges encountered in their application.

Abalone farming produces nutrient-rich sludge, and the frequent cleaning and removal of sludge from abalone tanks is labour and capital-intensive. This study aimed to assess the effect of culture methods and tank cleaning frequency on abalone growth, water quality, and sludge characteristics. The study was conducted for 16 weeks. Four treatments were used, namely, abalone cocultured with sea cucumber cleaned once (AS1) and twice weekly (AS2); abalone monoculture cleaned once (A1) and cleaned twice weekly (A2). Abalone (initial avg weight = 40.9 g) were maintained under commercial stocking conditions in flow through systems at a salinity of 35 ppt and fed a commercial formulated diet (Abfeed™) and fresh seaweed (Ulva lacinulata and Gracillaria gracilis). The stocking densities were 200 abalone m⁻² and 50 sea cucumbers m⁻². The sea cucumbers (initial average weight = 12.5 g) fed on the abalone faeces and leftover feed, which settled at the abalone tank's bottom (sludge). There was a significant interaction between the type of culture and the frequency of cleaning on abalone weight (F _(1,476) = 12.41, p < 0.001). Abalone in the A2 treatment group showed higher growth (p = 0.006) than those of the A1 treatment group, while abalone in AS1 had significantly higher growth (p < 0.001) than those in the AS2 treatment group. Also, abalone in AS1 showed higher growth (p = 0.026) than abalone in the A1 treatment. However, abalone in AS1 had growth similar (p = 0.53) to those in A2. The survival rate of the sea cucumbers was high, however, the sea cucumbers experienced a reduction in weight regardless of the treatment. This study showed that growth optimisation in abalone farming can be achieved by cleaning tanks twice instead of once weekly. However, when abalone are cocultured with sea cucumber, tanks need only be cleaned once a week without compromising abalone growth or water quality. The coculture of abalone and sea cucumber results in an additional aquacultured product, a significant reduction in labour and other associated costs of cleaning, without an additional cost of production.