Nutrient retention efficiencies in integrated multi-trophic aquaculture

One of the bottlenecks for commercial implementation of integrated multi-trophic aquaculture (IMTA) is the difficulty in quantifying its environmental performance. We reviewed a large body of literature to determine the variability in nutrient dynamics within different IMTA systems (open sea-cages, land-based flow-through and recirculating aquaculture systems), with the aim to provide a generic framework to quantify nutrient retention efficiencies in integrated aquaculture systems. Based on the eco-physiological requirements of the cultured species, as well as the response of “extractive” species to waste from “fed” species, the maximum retention efficiency was defined for a conceptual four-species marine IMTA system (fish–seaweed–bivalve–deposit feeder). This demonstrated that 79%–94% of nitrogen, phosphorus and carbon supplied with fish feed could theoretically be retained. In practice, however, various biological and environmental factors may limit retention efficiencies and thereby influence the bioremediation of IMTA systems. These biological (waste production, stoichiometry in nutrient requirements) and environmental (temporal and spatial connectivity) factors were therefore evaluated against the theoretical reference frame and showed that efficiencies of 45%–75% for closed systems and 40%–50% for open systems are more realistic. This study is thereby the first to provide quantitative estimates for nutrient retention across IMTA systems, demonstrating that a substantial fraction of nutrients released from fish culture units can be retained by extractive species and subsequently harvested. Furthermore, by adapting this framework to the design and the condition prevailing for a specific IMTA system, it becomes a generic tool to analyse the system's bioremediation potential and explore options for further improvement.publishedVersio

Carbohydrate utilisation by tilapia: a meta-analytical approach

Currently, studies reporting the digestibility of carbohydrates, starch and especially non-starch polysaccharides (NSP) in fish are scarce. Carbohydrate digestibility in the diet is largely dependent upon carbohydrate composition (starch vs. NSP). NSP are often considered to be indigestible and thus of no nutritional value. The present study reviews carbohydrates in fish feed, distinguishing between total carbohydrate, starch and NSP. Besides a qualitative approach, a meta-analysis was performed, compiling available data from digestibility studies on tilapia. Our meta-analysis confirms the negative effect of NSP on performance (FCR) and nutrient digestibility (crude protein, fat and energy). However, an average NSP digestibility of 24.3% was calculated in 95 cases. Out of these 95 cases, 88% of them showed a positive NSP digestibility. NSP digestibility was shown to contribute to energy digestibility. The digestion of NSP in fish is associated with fermentation in the gut, producing beneficial volatile fatty acids that are rapidly absorbed by the colonic lumen. Therefore, in diet formulation, digestibility and thus energy originating from NSP should be taken into consideration because NSP contribute to the energy needs of fish, here tilapia. Besides being an energy source, specific types of NSP may have immune-modulating and prebiotic effects and may be increasingly added to fish feed as modulators of fish health. We suggest that NSP is potentially (partly) digested by a wide range of fish species, especially by warm-water species with a long gut adapted to feeding on plant matter, as these factors favour gut fermentation.</p

Ammonium uptake by two fresh water periphytic microalgae immobilized in alginate beads

Microalgae play a significant role in nutrient recycling in aquatic ecosystem. Many species of microalgae have been isolated, cultured, and studied in laboratory to explore their potential use in aquaculture. In this study, two microalgae Spaerocystis sp. and Stigeoclonium sp., were isolated from aquaculture tanks in Aquatic Animal Health hatchery, Universiti Putra Malaysia. This study tested the capability of the microalgae cultured normally and immobilized in sodium alginate for uptake of ammonium. Between Spaerocystis sp. and Stigeoclonium sp., no difference was found on ammonium uptake. However, it was found that there was significantly higher (P<0.05) ammonium uptake by microalgae immobilized in sodium alginate than microalgae in normal culture. This higher uptake of ammonium by the immobilized microalgal beads maybe due to ammonium assimilation by microalgae and adsorption on alginate beads

Effect of dietary carbohydrate to lipid ratio on performance of Nile tilapia and enhancement of natural food in pond aquaculture

This study tested the effect of two diets differing in carbohydrate to lipid (CHO:LIP) ratio (4.7 vs. 19.5 g/g) on the contribution of natural food and the total fish production in tilapia ponds. Eight ponds, each divided into three equally sized compartments, were assigned to one of the two diets, which differed in CHO:LIP ratio but had the same digestible protein to digestible energy (DP:DE) ratio (15.5 and 15.6 g/MJ). Ponds were fed equal amounts of crude protein. Three feeding levels (no, low and high) were nested in each pond in a split plot design. Average body weight of fish at stocking was 90 g, and the duration of the experiment was 42 days. Increasing the CHO:LIP ratio had no impact on tilapia production. However, the feeding level influenced both biomass gain, specific growth rate and survival. The apparent digestibility coefficient (ADC) for fat and carbohydrate was influenced by dietary CHO:LIP ratio but ADC for energy was unaffected. Proximate analysis of fish body composition showed no effect of diet except for levels of ash. Diet had no effect on the organic matter composition of the faeces, and the contribution of natural food to fish nitrogen gain. Therefore, we postulate that changing the dietary non-protein energy source from lipid to carbohydrate does not have any impact on tilapia culture in semi-intensive ponds.</p

Ideotyping integrated aquaculture systems to balance soil nutrients

Due to growing land scarcity and lack of nutrient inputs, African farmers switched from shifting cultivation to continuous cropping and extended crop area by bringing fragile lands such as river banks and hill slopes into production. This accelerated soil fertility decline caused by erosion, harvesting and insufficient nutrient replenishment. We explored the feasibility to reduce nutrient depletion by increasing nutrient utilization efficiencies, while diversifying and increasing food production through the development of integrated aquaculture – agriculture (IAA). Considering the climatic conditions prevailing in Kenyan highlands, aquaculture production scenarios were ideotyped per agro-ecological zone. These aquaculture production scenarios were integrated into existing NUTrient MONitoring (NUTMON) farm survey data for the area. The nutrient balances and flows of the resulting IAA-systems were compared to present land use. The effects of IAA development on nutrient depletion and total food production were evaluated. With the development of IAA systems, nutrient depletion rates dropped by 23–35%, agricultural production increased by 2–26% and overall farm food production increased by 22–70%. The study demonstrates that from a bio-physical point of view, the development of IAA-systems in Africa is technically possible and could raise soil fertility and total farm production. Further studies that evaluate the economic feasibility and impacts on the livelihood of farming households are recommended

Onderzoek van Duitse bunkers uit de Eerste Wereldoorlog in Petit Bois Wijtschate (Heuvelland). Eindverslag van een toevalsvondst

Bij beheerswerken in Petit Bois, een bosgedeelte van het boscomplex rond Wijtschate, werden de ingangen van twee bunkers uit de Eerste Wereldoorlog vrijgelegd. Beide bunkers hebben vergelijkbare afmetingen en zijn opgetrokken in beton met golfplaten die de binnenruimtes overspannen

Growth, production and food preference of rohu Labeo rohita (H.)in monoculture and in polyculture with common carp Cyprinus carpio (L.) under fed and non-fed ponds

An experiment was carried out in 18 earthen ponds to investigate the effects of the addition of common carp Cyprinus carpio (L.) and artificial feed on natural food availability, food utilization and fish production in rohu Labeo rohita (Hamilton) ponds. Ponds were fertilized fortnightly with cow manure, urea and triple super phosphate. Rohu was stocked in all ponds at a density of 1.5 rohu m-2. All treatments were carried out in triplicate. Treatments were: rohu with and without formulated feed, rohu plus 0.5 common carp m-2 with and without feed, and rohu plus 1 common carp m-2 with and without feed. The time period between stocking and harvesting was four and half months. Stocking 0.5 common carp m-2 enhanced natural food availability in the pond, food utilization and rohu growth and production (P0.05) but increased zooplankton and benthic macroinvertebrate availability (P<0.001). Feed administration also enhanced growth of rohu and common carp (P<0.001). Rohu naturally ingests more phytoplankton than zooplankton but in the presence of formulated feed rohu shifted its natural food preference from phytoplankton to zooplankton. Common carp naturally ingests mainly zooplankton and benthic macroinvertebrate and small quantities of phytoplankton. However, when offered formulated feed, the latter becomes the preferred food item

Vermist in de Ypres Salient. Toevalsvondst langs de Ieperstraat In Wijtschate (West-Vlaanderen). Eindverslag van een toevalsvondst

Graafwerken in Wijtschate (gem. Heuvelland), gedaan in functie van de renovatie in 2016 van huisnummer 80 langs de Ieperstraat, bracht menselijke botresten en een militaire bottine aan het licht. De werken werden stil gelegd en een toevalsvondst werd gemeld. Het onderzoek van deze toevalsvondst heeft uitgewezen dat de resten wellicht toebehoorden aan een Franse militair (cavalerist of officier) die vermist is geraakt bij het begin van de Eerste Wereldoorlog bij de Duitse aanval op de Heuvelrug van Mesen. De resten waren zeer fragmentair bewaard, wat er wellicht op wijst dat deze in het verleden al eens verstoord werden, misschien bij de bouw van de woning die in 2016 gerenoveerd werd