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The microbial cells, which are linked to the surface and bound to the matrix of primary polysaccharides materials, are collectively called biofilms. The surface can be a medical device, water pipe, living tissue, and simply a natural aquatic environment. The assemblage of biofilms contains simple unicellular and multicellular organisms, like algae, protozoa, bacteria, and arthropods. The structure of biofilms fully depends on the light and grazing capability of the organism, nutrient availability, hydrodynamics of system, and most importantly the nature of the substratum. The introduction of substrata plays a significant role in the development of biofilm, and organic substrata facilitate more growth of microbial colonies on them. Biofilms are rich in single-cell proteins, which can be very easily harvested and digested by aquaculture species as natural feed sources. Most biofilms provide up to 40% protein, which satisfies the protein demands of many cultured finfish and shellfish species. Besides being a source of nutrition, the heterotrophic bacteria and microalgae also act as immune system modulators, growth enhancers, bioactive compounds, and dietary stimulants. Substrata also increase the survival rate by providing the attachment sites, shelter, and hiding places to aquatic animals. The biofilms play a significant role in the improvement of water quality parameters and in the reduction of pathogenic bacteria through nitrification of ammonia to less toxic nitrates. Therefore, biofilms provide a cheap source of nutrition and water quality control to a poor farmer for sustainable aquaculture. This chapter spotlights the importance of biofilms in the sustainable production of aquaculture.

Single cell protein: Sources, mechanism of production, nutritional value and its uses in aquaculture nutrition

Water quality in aquaculture has been considered to be an important factor that influences the growth and survival of fish in nursery to growout phase. A microalga, Chlorella vulgaris is utilized to filter chemical substances to maintain optimum water quality and growth of fish. The present study was conducted to know the efficiency of Chlorella vulgaris in maintaining water quality and growth of juvenile Siamese fighting fish (Betta splendens). As nutrient utilization capacity of immobilized microalgae is higher than the free floating microalgae, the experiment was consisted of 4 treatments which were control (blank beads), low (4-5 beads/mL) (T1), medium (10-12 beads/mL) (T2) and high (15-16 beads/mL) (T3) concentration of microalgae beads. It has been found that, in the control treatment, ammonium concentration initially reduced in medium rate (1.5 mg/L to 0.8 mg/L) but become slower (0.8 mg/L to 0.7 mg/L) in later days. But in first four days, reduction of ammonium and nitrite concentration was followed by T3, T2, and T1 and from day five to seven, both were slightly higher than previous day. On the other hand, PO4 3+ showed great reduction (60 mg/L) than the other treatment tanks. Highest SGR found in algal beads containing treatments than control treatment which were recorded as 4.58, 4.61, 4.57 and 3.60 in T1, T2, T3 and control treatment respectively. Results showed that, there was no significant difference (p < 0.05) in TAN, NO2-N, PO4-P, pH, DO and temperature among the microalgae beads containing treatments but significant difference (p < 0.05) found among control and microalgae beads containing treatments. It has been recommended to study economic feasibility of using microalgae beads to maintain the water quality in commercially important ornamental and aquaculture species especially in fish and shrimp hatchery for the larval rearing.

The contribution of heterotrophic bacteria to paniculate light absorption in the ocean has been traditionally considered insignificant as compared to that of phytoplankton and detritus. This view has been based on the general presumption that heterotrophic marine bacteria do not contain pigments with significant absorption in the visible spectral range. However, there exist heterotrophic bacteria that synthesize carotenoid pigments, and carotenoid-rich strains of bacteria have often been isolated from natural seawater samples taken in the open and coastal ocean. Because carotenoids absorb strongly in the blue spectral region, the heterotrophic bacteria may contribute more to marine light absorption than has been assumed. In order to make preliminary assessment of such a contri- bution, we measured the absorption of a strain of carotenoid-co ntaining heterotrophic bacteria (CHB) grown in the laboratory under differing conditions of light and nutrient availability. These measurements showed that absorption cross-sections of CHB in the blue could be at least twice, and possibly one order of magnitude, higher than those of non-pigmented heterotrophic bacteria (NHB). In addition, the absorption features of CHB were conserved under the differing light and nutrient conditions. We conclude that the role of heterotrophic bacteria in marine light absorption needs to be re-evaluated. This will require further laboratory studies to quantify the absorption cross-sections of marine bacteria with improved accuracy, as well as the development of a technique for the recog- nition and enumeration of CHB cells in the ocean.

Food quantity and quality are highly variable in natural systems. Therefore, their interplay and the associated effects on consumer population growth are important for predator–prey interactions and community dynamics. Experiments in which consumers were exposed to elemental nutrient limitations along food quantity gradients suggest that food quality effects on consumer performance are relevant only at high food quantities. However, elemental nutrients act differently on physiological processes than biochemical nutrients. So far, the interactive effects of food quantity and biochemical compounds on consumer performance have been insufficiently studied. We studied interactive effects of food quantity and biochemical food quality on population growth, including fecundity and survival, of the freshwater rotifer Brachionus calyciflorus. We hypothesised that these life history traits are differently affected by the availability of biochemical nutrients and that food quality effects gain importance with increasing food quantity. In a first experiment, we established food quantity and quality gradients by providing rotifers with different concentrations of a low‐quality food, the sterol‐free cyanobacterium Synechococcus elongatus, supplemented with increasing amounts of cholesterol. In a second experiment, food quantity and quality gradients were established by providing different proportions of two prey species differing in biochemical food quality, i.e. S. elongatus and the lipid‐rich alga Nannochloropsis limnetica, at different total food concentrations. We found that the effects of cholesterol supplementation on population growth increased with increasing food quantity. This interactive effect on population growth was mainly due to food quality effects on fecundity, as effects on survival remained constant along the food quantity gradient. In contrast, when feeding on the mixed algal diet, the food quality effect associated with increasing the proportion of the high‐quality alga did not change along the food quantity gradient. The data on survival and fecundity demonstrate the missing interactive effect of food quantity and quality on population growth, as both traits were oppositely affected. Survival was affected by food quality primarily at low food quantity, whereas food quality effects on fecundity were stronger at high food quantity. Our results highlight the significance of essential biochemicals in mediating the interactive effects of food quantity and quality on population growth. The interplay between food quantity and biochemical food quality limitation seems to influence resource allocation patterns in order to optimise survival or reproduction, which may strongly affect population dynamics in variable environments. As opposed to exploring the function of a single nutrient via supplementation, using algae mixtures allowed us to assess food quality effects on consumer performance in a more natural context by taking potential interactive effects of multiple co‐limiting nutrients into account.

Reprogramming of<i>Vibrio harveyi</i>gene expression during adaptation in cold seawater

The potential of Marine Actinobacteria particularly Streptomyces as a single cell protein (SCP) feed for the growth of ornamental fish, Xiphophorus helleri has been investigated. The Streptomyces strains used as SCP were isolated from the marine sponges, namely Callyspongia diffusa, Mycale mytilorum, Tedania anhelans and Dysidea fragilis. Six SCP feeds were prepared and their effects were compared with those of control diet. After 30 days of feeding trials, the growth parameters including absolute growth rate, specific growth rate and feed conversion efficiency were found to be significantly (P<0.001) higher in groups that received SCP feed than those of control one, whereas feed conversion ratio was lower. Thus it was found that in addition to being effective antibiotic agents against harmful pathogens, Streptomyces could also promote the growth of fish effectively. Marine Actinobacteria, particularly Streptomyces, could play an important role as a single cell protein (SCP) in aquaculture nutrition and is a promising microbe for the development of marine biotechnology.

Animal and food characteristics, which exercise an influence on protein utilisation, are discussed in the first part of our paper. Maintenance requirements have been related to the metabolic body weight and amount to 3.0 g DCP/kg WI-11 resp. 3.25 g PDI/kg W 0. 15. Protein requirements for growth depend on the amount of protein deposited by the animal. Protein deposition is higher in bulls than in steers, and higher in late-maturing than in early-maturing breeds. Moreover, protein accretion has been shown to be age-dependent, The information on the efficiency of utilisation of absorbed amino acids for tissue synthesis is still insufficient. Based on the data of INRA, a value of 0.63 has been adopted for our calculations. Amino acids absorbed from the small intestine of ruminants are supplied by undegraded food proteins and by microbial proteins synthesised in the rumen. The available data on protein degradation indicate that as much as 85 per cent and as little as 30 per cent may be degraded in the rumen. The synthesis of microbial protein is essentially governed by the energy supply and by the availability of nutrients, especially nitrogen. To simplify matters, the quantity of microbial protein has been related to the DOM intake, the relevant figure being 135 g microbial crude protein per kg DOM. The true digestibility of (undegraded) food protein is obtained from a regression equation. The values resulting from this equation are in the range of 60 95 per cent. With regard to the true digestibility of microbial protein, a value of 70 per cent is adopted. Examples of the co-ordination of protein requirements and protein supply are given in the second part of the paper. A factorial approach has been used for this purpose. Rations are formulated for two breeds (Friesian and Charolais) at the beginning and the end of the fattening period. The basic feedstuffs to be used are grass silage and maize silage ; a cereal and an meal are assumed to be available concentrates. With the grass silage diet, a forage : concentrate ratio of 60 : 40 (Friesians) resp. 40 : 60 (Charolais) was chosen. With the maize silage diets, the corresponding ratio was 80 : 20 and 60 : 40 for the two breeds. The factorial analysis shows the required crude protein content to be highest for the young animals on the grass silage diet (15.8 15.9 per cent CP in DM). The corresponding value for young animals on the maize silage diets is 14.5 per cent resp. 15.1 per cent for Friesian and Charolais bulls. The appropriate CP content for the heavy animals varies only little with diet and breed (12.0 13.0 per cent). The omission of the oil meal mixture in the second half of the fattening period leads to a deficit in rumen degradable nitrogen. In our model, this gap is filled by the addition of urea. In our example rations, the utilisation of feed nitrogen (N deposition divided by N intake) can be assumed to be 0.22 0.26 at the beginning and 0.13 0.16 at the end of the fattening period.

Aquaponics is a cultivation system that combines aquaculture and agricultural hydroponics. This study investigated water quality changes and growth of fish (siberian sturgeon) and leafy vegetables (basil and four leafy vegetables) through the use of nitrifying autotrophic bacteria alone (Auto+CO2)and the mixed use of heterotrophic and autotrophic microorganism (Hetero+HBFT) in operation of aquaponic system. After basil stocking (5-8 weeks) in EXP1, Auto+CO2 experimental groups showed rapid water quality stabilization for about 2 weeks compared to Hetero+HBFT groups, but the lattergroups showed significantly higher growth of both fish and basil (P0.05).. In EXP2 (9-12 weeks), the growth factors of fish and 4 kinds of european lettuce cultivars in Hetero+HBFT experimental groups were higher than Auto+CO₂ groups. In hematological ananlysis [hematocrit (PCV, %), hemoglobin (g/dL), GOT (U/L), GPT (U/L), ALB (g/dL), GLU (mg/dL), plasma Na, K, Cl (mEq/L) and inorganic phosphorus (mg/dL)] between two experimental groups, all items were not significantly different at the end of the experimental period (P0.05). This study shows that for aquaponics water quality management, it is more effective to use it in combination with heterotrophic bacteria rather than autotrophic bacteria alone to stabilize water quality.

Occurrence and ecological impact of microplastics in aquaculture ecosystems

Food quantity–quality interactions determine growth rates and reproductive success of consumers and thereby regulate community dynamics and food web structure. Predator–prey models that shape our conceptual understanding of foraging ecology typically rely on the parametrization of fixed consumer responses to either food quantity or food quality. In nature, however, consumers optimize their fitness by responding simultaneously to changes in food quantity and quality. Therefore, we assessed consumer responses to changing food environments using a new fitness optimization model that accounted for food quality–quantity interactions to better capture the regulatory flexibility of consumers. Our simulations demonstrated that the impact of food quality on important consumer traits can be altered or even reversed by changes in food quality. Low food quality, for example, affected feeding rates negatively at low food concentrations but triggered surplus feeding at high food concentrations. The scope of surplus feeding was thereby mainly dependent on dynamics of nutrient digestion and in contrast to previous assumptions, energy costs of feeding played a minor role. Further, the regulation of digestive enzyme production, a crucial factor determining assimilation efficiencies, was strongly dependent on whether nonessential or essential nutrients were limiting growth. Consequently, not only the degree but also the type of nutrient limitation mediated the impact of the food environment on consumers’ fitness. At the community level, food quality was key in shaping predator–prey biomass ratios. High food qualities resulted in top‐heavy systems with larger consumer than prey biomass. Decreases of prey digestibility or the availability of essential nutrients, however, triggered a switch from inverted to classical pyramid shapes of bi‐trophic systems. The impact of food quantity on trophic transfer and emerging structural ecosystem properties thus critically hinges on behavioral and physiological responses of consumers. The inclusion of the regulatory flexibility of consumers is therefore an essential next step to improve predator–prey models and our conceptual understanding of trophic interactions.

A feeding trial which lasted for eight weeks was conducted to investigate the effects of diludine such as growth promoter on feed efficiency, muscle structure and proximate composition of juvenile rainbow trout. Diludine was added at 0.0(D0) 0.2(D1), 0.5(D2) and 1(D3) g kg-1 to a casein-based diet, and every diet was given to the triplicated groups of juvenile rainbow trout. At the end of experiment, it was determined that a significant improvability existed for both growth and feed utilization in fish fed diets supplemented with diludine (p < 0.05). Similarly, different concentration of diludine affected the densitometric quantification of myofibrillar proteins in fish muscle according to results obtained by Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The mean value of fiber diameters significantly increased in skeletal muscle by means of the increasing concentration of diludine. The histological results also showed hypertrophic adipocytes in skeletal muscle of fish fed D2 and D3 diets. The lowest elasticity values were observed in fish fed control diet while those fed D3 diet had highest elasticity values. On the other hand, no differences were found between fish fed experimental diets in terms of survival rate and all fish exhibited similar proximate composition for protein, lipid, moisture and ash. Consequently, it may be suggested that dietary diludine supplementaion up to 1 g kg-1 concentration in the diets have positive impacts on growth of rainbow trout juvenils and the better growth in the fish fed with diludine supplements could be arise from muscle characteristics, in particular changes in fibres than proximate composition of the muscles.

The objective of the study was to investigate the change of biofilm characteristics when implementing the procedure of partial nitrification. A ratio control strategy (DO/NH4+-N) was taken to achieve partial nitrification, and biofilm samples were obtained at 10.27%, 52.12%, and 93.54% of the nitrite accumulation rate. The amount and spatial distribution of total bacteria, ammonia oxidizing bacteria (AOB), and nitrite oxidative bacteria (NOB) were observed by fluorescence in situ hybridization (FISH) and confocal laser scanning microscope (CLSM) through a three-dimensional excitation emission matrix (EEM) to observe the secretion and composition changes of extracellular polymer substances. Ratio control successfully enriched AOB and achieved partial nitrification under conditions when NOB was not completely washed. Heterotrophic bacteria and nitrifying bacteria coexist in the biofilm. The heterotrophic bacteria were in the outer layer, but nitrifying bacteria were distributed in the biofilm surface at 6-25 μm. During the process of short-range nitrification, the AOB/NOB value gradually increased, and the stable operation period was as high as 15.56. During the operation of the reactor, EPS and microbial flora changes are closely related. When microbial activity decreased, EPS secretion decreased. During the stable operation period of partial nitrification, NOB and other bacteria that are non-resistant to high nitrite nitrous acid declined, and the fluorescence intensity of aromatic protein-like bacteria decreased. However, the three-dimensional fluorescence spectra showed that the chemical composition of EPS was not obvious during the process of partial nitrification.

The present investigation was an attempt to understand the distribution pattern of Streptomycetes in the five selected sea weed collected from Kovalam coast and the effect of isolated Streptomycetes as Single Cell Protein that has been incorporated into the artificial feed on growth of juveniles of Brachydanio rario. Food conversion efficiency and food conversion ratio were determined. From the experiment it is clear that microbial Single Cell Protein can be used to replace the fishmeal to certain extent in the artificial feeds. Keywords: Marine streptomycetes , Seaweeds, Single cell protein, Growth, Fish, Brachydanio rario

Experiments were conducted on the response of Cyprinus carpio to Artemia nauplii, mixed zooplankton and Yeast (single cell protein). The fish was fed two quantities of each diet, 100 and 150 ml artemia; 50-100 ml and 150-200 ml zooplankton; and 185 -195 and 200-250 ml yeast. They were fed twice daily There was no significant variation (P>0.05) in the Specific growth Rate, Mean Weight Gain of fish fed artemia and mixed zooplankton while there was significant variation in fish fed yeast. The growth of the fish with zooplankton diet showed a highly positively correlated (r2 = 0.999; P0.05). As for the artemia diet growth correlated positively although it was poor (r2 = 0.071). The two levels fed varied significantly (P < 0.05). There was a strong positive correlation between zooplankton and yeast (r = 1; P>0.05), and artemia and yeast (r = 1; P0.05) in the growth of fish. In comparing the Mean Final Weight and Specific Growth Rate of the three diets there was no significant difference (P>0.05). The percentage survival of fish fed the varying diets varied significant. The zooplankton diet is therefore more suitable for raising Cyprinus carpio fry. It has the advantage of being cheaper and easily cultured in tanks and ponds. Keywords: Response, Artemia salina, mixed zooplankton, yeastNigerian Journal of Fisheries Vol. 5 (1) 2008: pp. 63-72