Abstract
Shrimp based mangrove-aquaculture (silvo-aquaculture) is practiced in many countries of the world and leaf litter of different mangrove tree species is a potential nutrient source in these systems. The present study evaluated the effects of mangrove leaf litter from four mangrove species (Sonneratia apetala, S. caseolaris, Avicennia officinalis and Heritiera fomes) on the production of juvenile shrimp (Penaeus monodon) with and without supplemental feed. Fifteen-day-old post larvae (PL15) with an average weight of 0.01 g were reared in 1100 L fibre-reinforced polyethylene tanks containing 1000 L of 10 ppt saline water and a water depth of 0.9 m. Leaf litter with or without supplemental feed was applied to the tanks according to a 4 × 2 factorial design. The PLs were stocked at a density of 100 per tank and the experiment was conducted for 4 weeks without any exchange of water. Both mangrove species and feed application affected shrimp performance and water quality parameters except dissolved oxygen (DO), chemical oxygen demand (COD) and zoo-plankton concentration. The average survival rate of juvenile shrimp ranged from 86 to 94% in the treatments with both leaf litter and feed, 75–82% in the treatments with only leaf litter and 88% in the treatment with only feed. However, 100% mortality was observed in the treatment without any leaf litter or supplemental feed. Combined, leaf litter and feed resulted in 21 to 33% higher weight gain of shrimp PL than based on the combined contributions of leaf litter only or feed only, indicating synergism. Among the different mangrove species, S. apetala (23.1%) contributed the highest to total weight gain followed by A. officinalis (21.6%), S. caseolaris (21.6%) and H. fomes (10%). The lower feed conversion ratio (FCR) (0.18–0.27) in the treatments combining leaf litter and supplemental feed as compared to the feed-only treatment (0.41) indicated that leaf litter (directly or by stimulating natural food production) contributed to supplemental feeding. The growth of phytoplankton also appeared to contribute in low FCR as evidenced by a positive correlation (P < 0.001, r = 0.681⁎⁎) between phytoplankton concentration and shrimp weight gain. The synergistic effect between leaf litter and supplemental feed can help the farmer to minimize the shrimp production cost by lowering the feed input and enhancing mangrove three coverage on pond dikes as an inexpensive source of natural food.
Highlights
Mangroves are highly productive ecosystems in terms of primary and secondary productivity in the coastal waterbodies of the tropics and subtropics
The experimental results showed the significance of leaf litter of mangrove species as source of natural food for the shrimp post larvae (PL)
The survival rate ranged from 76 to 94% where the highest survival rate was observed for Sonneratia apetala (Sa)-F and the lowest was for ScnF (Fig. 1a)
Summary
Mangroves are highly productive ecosystems in terms of primary and secondary productivity in the coastal waterbodies of the tropics and subtropics. Mangrove leaf litter is a natural food for shrimp (Gatune et al, 2014; Gatune et al, 2012; Nga et al, 2006; Hai and Yakupitiyage, 2005). The combination of natural food and formulated feed should have a positive effect on all the production parameters of shrimp as observed by Porchas-Cornejo et al (2012). A positive synergistic effect, if any, would make shrimp aquaculture more productive in an environ mentally friendly way Such synergy could help to align interests of farmers and mangrove restoration, and could be an effective way to minimize the conflicts between shrimp culture and mangrove loss (Ahmed et al, 2017; Bosma et al, 2014; Primavera, 2000). How ever, the positive and negative effects of mangrove leaf litter, as well as any synergistic effects, might differ depending on the species of mangrove
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