M.C.J. Verdegem

Reducing Water Use for Animal Production through Aquaculture

Animals fed formulated diets indirectly consume large quantities of water. Globally, about 1.2 m3 of water is needed to produce 1 kg of grain used in animal feeds. Cattle in feedlots consume about 7 kg of feed concentrate to gain 1 kg in weight. For pigs this is close to 4 kg and for poultry slightly more than 2 kg of concentrate. Fish or crustaceans require less than 2 kg of grain concentrate for each kg produced, making them the most efficiently producing animals in terms of feed-associated water use. Non-feed-associated water use can also be considerable, and a comparison was made in total water use between aquatic and terrestrial animals. On-farm water use for terrestrial animals, including drinking, but excluding water for cooling animals or cleaning their sheds is only 1% of feed-associated water use. However, on-farm water use in aquaculture can be very high, attaining values of up to 45 m3 per kg produced in ponds. Intensification of aquaculture reduces on-farm water use per kg product, and only intensive aquaculture production systems are equally water-efficient as terrestrial animal farming systems. Within existing aquaculture pond systems reductions in water use can be achieved through (1) selection of feed ingredients that need little water to be produced; (2) enhancement of within-system feed production through periphyton-based technology; and (3) integration of aquaculture with agriculture. Still, these approaches will not make pond aquaculture more water-efficient than terrestrial animal production systems. That can only be attained in recirculating aquaculture systems and systems producing fish as a by-product of wastewater treatment. Currently, the most promising approach is to concentrate on further development of brackish and marine aquaculture, as such systems use small or negligible amounts of non-feed-associated fresh water.

A comparison of fertilization, feeding and three periphyton substrates for increasing fish production in freshwater pond aquaculture in Bangladesh

Abstract A polyculture trial was conducted in earthen ponds in Bangladesh to compare traditional aquaculture techniques (fertilization only or fertilization plus feeding) with a combination of the same techniques and periphyton substrates. Three substrates (bamboo, jutestick and bamboo side shoot) were tested. Rohu ( Labeo rohita ), catla ( Catla catla ) and kalbaush ( L. calbasu ) were stocked at a 60:40:15 stocking ratio and at a total stocking density of 11,500 per hectare in 15 earthen ponds with five treatments: standard fertilization as input (Control), control plus supplemental feeding with rice bran and oil cake (Feed), control plus bamboo substrate (Bamboo), control plus jutestick substrate (Jutestick) and control plus bamboo side shoot substrate (Kanchi). Water quality, plankton and periphyton were monitored throughout the experiment. Significantly higher ammonia concentrations were recorded in Control and Feed treatments. The chlorophyll a concentration of pond water was significantly higher in the Feed treatment than in the Jutestick treatment. Dry matter content and mean abundance of the periphyton communities were higher in the first and the last month of the experiment without significant difference among the three substrate types. Periphyton chlorophyll a concentrations per unit surface area did not vary significantly among different substrate types but increased throughout the experimental period and decreased with increasing water depth. Specific growth rates of rohu and catla were higher in Substrate and Feed treatments than in the Control treatment. Combined net yields of fish in Control, Feed, Bamboo, Jutestick and Kanchi treatments were 1226, 1960, 2098, 2048 and 2032 kg ha −1 135 day −1 , respectively. Production in substrate systems was significantly higher (ANOVA, P

The effect of periphyton and supplemental feeding on the production of the indigenous carps Tor Khudree and Labeo fimbriatus

Two experiments were conducted, one with the herbivorous mahseer Tor khudree and another with the fringe-lipped carp Labeo fimbriatus to study the effect of feeding and periphyton on their growth and production. Twelve tanks (25 m2) with mud bottoms and 0 (control), 98 (low density) or 196 (high density) bamboo poles tank−1 were used. Mahseer (initial wt. 3.5 g) and fringe-lipped carp (initial wt. 0.73 g) stocked at 25 fish tank−1 were reared for 90 and 60 days, respectively. Fish in half of the tanks received a pelleted feed (35% protein) at a ration of 5% body weight day−1. Water was monitored daily for dissolved oxygen, pH, temperature, and Secchi disc visibility, and weekly for ammonia, nitrate, phosphate, and alkalinity. Periphyton dry matter, ash, and chlorophyll content were quantified fortnightly. Periphyton biomass, measured as total pigment (chlorophyll-a+pheophytin), decreased with time in both experiments indicating effective grazing by the fish. In the control treatment (without supplemental feed and substrates), mahseer grew to a final weight of 30.8±0.9 g and fringe-lipped carp to 19.1±1.1 g (mean±S.D.). Supplemental feeding alone resulted in higher final mean weight of mahseer and fringe-lipped carp of 38.3±0.6 and 22.9±1.2 g, respectively. The provision of substrates resulted in final mean weights of mahseer of 36.0±5.7 and 36.1±1.3 while that of fringe-lipped carp were 22.8±1.2 and 22.5±1.9 (low and high density, respectively). Net production of mahseer with substrates was 41% and 51% higher, and that of fringe-lipped carp was 43% and 75% higher than in the control (low and high density, respectively). The combination of substrates and supplemental feed resulted in mean final weights of mahseer of 40.3±0.4 and 39.7±1.2, and of fringe-lipped carp of 23.6±1.4 and 25.5±0.1 (low and high substrate density, respectively). Production of mahseer with a combination of substrates and feeding was 71% and 54% higher, and of fringe-lipped carp, it was 85% and 87% higher than in the control (low and high density, respectively). It is concluded that the provision of substrates can reduce the need for artificial feed and can be an alternative to feeding in the culture of herbivorous fish.

The effects of artificial substrates on freshwater pond productivity and water quality and the implications for periphyton-based aquaculture

As a first step in assessing the viability of periphyton-based fish production in South Asian pond aquaculture systems, the effects of artificial substrates on development of periphyton and on water quality were evaluated. Earthen ponds (10 × 7.5 m) were provided with an artificial substrate constructed from poles of either bamboo, kanchi or hizol tree branches (1.0 m 2 artificial substrate per m 2 pond surface). Higher periphyton biomass, in terms of dry matter (DM) (4.9 mg cm ‐2 ) and chlorophyll a (11.5 µ gc m ‐2 ) developed on hizol and bamboo, respectively. Periphyton ash content was higher on hizol (41%) than on the other two substrate types (29%). Protein content of the periphyton growing on bamboo (38% of ash-free dry matter (AFDM)) was 50% higher than that on the other two substrate types. Maximum periphyton productivities of 1.01, 1.38 and 1.03 g C m ‐2 d ‐1 were obtained for bamboo, hizol and kanchi substrates, respectively. Taxonomic composition of periphyton showed a rapid development of a relatively stable community with few differences between the substrate types. In total, 56 genera of algal periphyton and 35 genera of phytoplankton were identified. Based on a periphyton productivity estimate of 2.2‐2.8 g AFDM m ‐2 d ‐1 , periphyton alone can sustain an estimated fish production of 5000 kg ha ‐1 year ‐1 through the addition of a substrate area equivalent to 100% of the pond surface area.

Organic matter sedimentation and resuspension in tilapia (Oreochromis niloticus) ponds during a production cycle

The rates of sedimentation and resuspension of organic carbon and total nitrogen were measured in earthen fishponds, based on nutrient input, water quality parameters and fish size and biomass. Material collected in sediment traps and soil samples were analyzed for organic carbon, total nitrogen, iron and aluminum concentrations. A dilution analysis method was used to differentiate between sedimented and resuspended particles. The rates of sedimentation and resuspension estimated from total solids increased during the experiment, ranging from 49.8 to 218.1 g/m2 per day in the case of sedimentation and from 39.2 to 160.0 g/m2 per day in the case of resuspension. Although fish weight increased through time, the relative resuspension did not change significantly, ranging from 42 to 47% of the total collected material. Total solids sedimentation and resuspension rates were highly correlated (P≤0.01) to fish weight and biomass, chlorophyll-a, total suspended solids, total feed input and Secchi disk visibility.

The impact of rearing environment on the development of gut microbiota in tilapia larvae

This study explores the effect of rearing environment on water bacterial communities (BC) and the association with those present in the gut of Nile tilapia larvae (Oreochromis niloticus, Linnaeus) grown in either recirculating or active suspension systems. 454 pyrosequencing of PCR-amplified 16S rRNA gene fragments was applied to characterize the composition of water, feed and gut bacteria communities. Observed changes in water BC over time and differences in water BCs between systems were highly correlated with corresponding water physico-chemical properties. Differences in gut bacterial communities during larval development were correlated with differences in water communities between systems. The correlation of feed BC with those in the gut was minor compared to that between gut and water, reflected by the fact that 4 to 43 times more OTUs were shared between water and gut than between gut and feed BC. Shared OTUs between water and gut suggest a successful transfer of microorganisms from water into the gut, and give insight about the niche and ecological adaptability of water microorganisms inside the gut. These findings suggest that steering of gut microbial communities could be possible through water microbial management derived by the design and functionality of the rearing system.

The Colonization Dynamics of the Gut Microbiota in Tilapia Larvae

The gut microbiota of fish larvae evolves fast towards a complex community. Both host and environment affect the development of the gut microbiota; however, the relative importance of both is poorly understood. Determining specific changes in gut microbial populations in response to a change in an environmental factor is very complicated. Interactions between factors are difficult to separate and any response could be masked due to high inter-individual variation even for individuals that share a common environment. In this study we characterized and quantified the spatio-temporal variation in the gut microbiota of tilapia larvae, reared in recirculating aquaculture systems (RAS) or active suspension tanks (AS). Our results showed that variation in gut microbiota between replicate tanks was not significantly higher than within tank variation, suggesting that there is no tank effect on water and gut microbiota. However, when individuals were reared in replicate RAS, gut microbiota differed significantly. The highest variation was observed between individuals reared in different types of system (RAS vs. AS). Our data suggest that under experimental conditions in which the roles of deterministic and stochastic factors have not been precisely determined, compositional replication of the microbial communities of an ecosystem is not predictable.

The Effects of Periphyton, Fish and Fertilizer Dose on Biological Processes Affecting Water Quality in Earthen Fish Ponds

The potential of periphyton-based aquaculture in South Asia is under investigation in an extensive research program. This paper is a further analysis of data from four experiments carried out in that framework, to explore periphyton, fish and fertilizer dose effects on water quality. Factor analysis and ANOVA models applied to a data matrix of water quality parameters in ponds with and without artificial substrates (bamboo poles and kanchi sticks), with and without fish (filter feeders catla and rohu, with and without bottom feeder kalbaush), and with a standard or 50% increased fertilizer dose, allowed us to identify the underlying ecological processes governing this novel periphyton-based pond system, and construct conceptual graphic models of the periphyton–environment relationships observed. We clearly established that the phosphorus flow is mainly linked to phytoplankton activity in the water column and decomposition on the pond bottom, while nitrogen flow is mainly linked to autotrophic (photosynthesis) and heterotrophic (decomposition and nitrification) processes that take place in the periphyton in addition to the water column and pond bottom. Consequently, disruption of the pond bottom by bottom feeding fish primarily promoted phosphate cycling and phytoplankton, while periphyton development on the supplied substrates and fertilization mainly improved oxygen balance and nitrogen related processes developing in the water column. The use of bamboo poles led to better results than kanchi sticks, related to the greater autotrophic periphyton development on bamboo and to the larger surface of bamboo poles that facilitate fish grazing and periphyton dislodgment that in turn have a renewal effect on periphyton. Stocking bottom feeding fish produces a fertilizing effect through the food web that benefits the filter-feeding fish and that makes it unnecessary to increase the dose of inorganic and organic fertilizers applied to the ponds. Thus, the output of this analysis will help the fish farmers in resource constrained countries to improve their production in periphyton-based ponds just by choosing bamboo substrates, stocking a bottom feeder fish together with the filter feeders, and saving money on fertilizers.

Comment on ‘Water footprint of marine protein consumption—aquaculture’s link to agriculture’

In their article ‘Freshwater savings from marine protein consumption’ (2014 Environ. Res. Lett. 9 014005), Gephart and her colleagues analyzed how consumption of marine animal protein rather than terrestrial animal protein leads to reduced freshwater allocation. They concluded that future water savings from increased marine fish consumption would be possible. We find the approach interesting and, if they only considered marine capture fisheries, their analysis would be quite straightforward and show savings of freshwater. However, both capture fisheries and aquaculture are considered in the analysis, and the fact that marine aquaculture is assumed to have a zero freshwater usage, makes the analysis incomplete. Feed resources used in marine aquaculture contain agriculture compounds, which results in a freshwater footprint. To correct this shortcoming we complement the approach taken by Gephart and her colleagues by estimating the freshwater footprint (WF) for crops used for feeding marine aquaculture. We show that this is critically important when estimating the true freshwater footprint for marine aquaculture, and that it will be increasingly so in the future. We also further expand on aquaculture’s dependency on fish resources, as this was only briefly touched upon in the paper. We do so because changes in availability of fish resources will play an important role for feed development and thereby for the future freshwater footprint of marine aquaculture.

Probiotic legacy effects on gut microbial assembly in tilapia larvae

The exposure of fish to environmental free-living microbes and its effect on early colonization in the gut have been studied in recent years. However, little is known regarding how the host and environment interact to shape gut communities during early life. Here, we tested whether the early microbial exposure of tilapia larvae affects the gut microbiota at later life stages. The experimental period was divided into three stages: axenic, probiotic and active suspension. Axenic tilapia larvae were reared either under conventional conditions (active suspension systems) or exposed to a single strain probiotic (Bacillus subtilis) added to the water. Microbial characterization by Illumina HiSeq sequencing of 16S rRNA gene amplicons showed the presence of B. subtilis in the gut during the seven days of probiotic application. Although B. subtilis was no longer detected in the guts of fish exposed to the probiotic after day 7, gut microbiota of the exposed tilapia larvae remained significantly different from that of the control treatment. Compared with the control, fish gut microbiota under probiotic treatment was less affected by spatial differences resulting from tank replication, suggesting that the early probiotic contact contributed to the subsequent observation of low inter-individual variation.