Dietary carbohydrate and faecal waste in the Nile Tilapia (Oreochromis niloticus L.)

Public concerns about environmental pollution are putting increasing pressure on fish farms to treat their wastewater before release. The wastewater produced by the fish can also deteriorate water quality within the system. Aquaculture waste can be divided into solid waste and dissolved waste.Faeces ismain sources of solid waste. An increased consistency of faeces may improve its removal efficiency, thereby improving water quality. The removal efficiency of faeces by a collector (settling tank and/or Choubert) was proposed as an indicator for faeces consistency. Manipulation of the diet composition changed faeces consistency in tilapia. Soluble non-starch polysaccharide increased digesta viscosity and reduced faeces removal efficiency. Insoluble non-starch polysaccharide did not change faeces removal. Replacement of native starch by gelatinized starch improved faeces removal efficiency. Fermentation and viscosity of digesta are the main parameters affecting faeces consistency. An increased faeces removal, induced by dietary composition, lowered the organic matter load into the system, thereby increasing nitrification and dissolved oxygen. A detailed investigation on fermentability and viscosity of different ingredients can provide insight in characterization of faeces, thereby giving suggestion for diet formulation geared to maximize solid removal

Effect of gelatinization degree and inclusion level of dietary starch on the characteristics of digesta and faeces in Nile tilapia (Oreochromis niloticus (L.))

Higher faeces removal efficiency can help and reduce the negative impact of faecal waste on water quality and on the environment. Physicochemical properties of feed ingredients/nutrients may change the faeces characteristics and the ratio of removed to non-removed solids. The aim of this study was to assess what physicochemical properties of the diet (viscosity, fermentation and dry matter) influence faeces characteristics and faeces removal using Oreochromis niloticus (L.) as the test animal. Four experimental diets were formulated by the addition of two types of starch differing in gelatinization degree (gelatinized and native) and two levels (high and low) of starch to a basal diet according to a 2 × 2 factorial design. The diets were assigned to 16 tanks with 40 fish each, with four replicates for each diet. Replacement of native starch by gelatinized starch improved faeces removal rate, growth and digestibility (P <0.01), but reduced fermentation (P <0.05) at the end of the intestine. Addition of gelatinized starch did not change viscosity and dry matter of the digesta at the end of the intestine. A high level of starch in the diet also increased digestibility, growth and faeces removal percentage (P <0.05). Fermentation and dry matter content at the end of the intestine were not influenced by a high starch diet, but viscosity was higher at the high level of starch inclusion. Volatile fatty acid levels in the stomach of Nile tilapia were high in the treatments with gelatinized starch. In conclusion, intestinal fermentation induced by native starch had a negative impact on faeces removal efficiency. A higher inclusion level of starch resulted in a higher viscosity of the digesta, leading to higher faeces removal efficienc

Time related alterations in digestibility and faecal characteristics as affected by dietary composition in the Nile tilapia (Oreochromis niloticus L.)

After being shifted to a new diet, time related alterations in digestibility, faecal waste production and faeces recovery in Nile tilapia were assessed in relation with dietary ingredient composition. Four experimental diets were formulated according to a 2 by 2 factorial design: two starch inclusion levels (20 or 40%) and two maize starch types (native versus gelatinized). After introduction to the experimental diets, faeces were collected weekly from Week 2 till 6 using settling tanks. Digestibility of ash, organic matter and dry matter increased with time (P <0.001). For organic and dry matter the time related alteration in digestibility were different between both starch types (P <0.05). All faecal waste characteristics altered with time (P <0.01). The incline in faeces recovery with time was affected by starch type (P <0.01); being the largest at the 40% gelatinized maize diet. In conclusion, the minimal length of the adaptation period in digestibility studies for obtaining unbiased digestibility estimates is dependent on diet composition, in this study with Nile tilapia 4 weeks for diets with gelatinized starch and 6 weeks with native starch

Type of dietary fibre (soluble versus insoluble) influences digestion, faeces characteristics and faecal waste production in Nile tilapia (Oreochromis niloticus L.)

The physico-chemical properties of nutrients influence the physical characteristics of faeces and thus may affect waste removal efficiency. The aim of this study is to assess the effect of type of non-starch polysaccharide (NSP) on digesta viscosity, faeces recovery and nutrient digestibility in Nile tilapia. Insoluble (cellulose) and soluble (guar gum) NSPs were included separately and combined at a level of 8%, thereby formulating four experimental diets. The diets were assigned to 16 tanks with 35 fish each, with four replicates for each diet. Cellulose inclusion did not influence digesta viscosity, growth and digestibility of protein and starch and tended to increase faeces recovery (P=0.06). Guar gum inclusion increased digesta viscosity and reduced the growth and digestibility of protein, fat and starch (

Comparison of faecal collection method with high and low quality diets regarding digestibility and faeces characteristics measurements in Nile tilapia

The need for unbiased digestibility estimation has led to the development of a number of faeces collection methods. However, there is still a large variation in apparent digestibility coefficient (ADC) of diet/ingredients between these methods. This study investigated the impact of dietary quality on ADC and faeces recovery measurements obtained by two faecal collection methods (Choubert and settling tank). The fish were fed five diets: a control diet as high-quality diet, two levels of dried duckweed (20% and 40%) and two levels of fresh duckweed (20% and 40%), which were added to the control diet, as low-quality diets. Apparent digestibility coefficient estimates were highly correlated (r>0.95) between both faecal collection methods. For all diets the ADC estimates were higher when using settling tanks compared with Choubert collectors. For the control diet differences in ADC between two collectors were small, but by inclusion of duckweed these differences increased. The recovery percentage of faeces was not correlated between both faecal collection methods (r=0.22, P=0.41). The estimated recovery percentage of faeces by settling tanks was about three times higher than by Choubert. In conclusion, the differences in ADC and faeces recovery measured by two faecal collection methods depend on diet qualit

Digestibility, faeces recovery, and related carbon, nitrogen and phosphorus balances of five feed ingredients evaluated as fishmeal alternatives in Nile tilapia, Oreochromis niloticus L.

This study shows that alternatives for fishmeal in a fish diet affect not only fish growth but also faeces stability and nitrogen (N) and phosphorus (P) waste production. Wheat gluten diet (WGD), soybean meal extract diet (SBE), soybean meal diet (SBM), duckweed diet (DWD) and single-cell protein diet (SCP) were evaluated as a fishmeal replacement on a 15% weight weight(-1) basis in tilapia diets. Fishmeal replacement affected dry matter (dm), protein, ash and P digestibility significantly. Faeces recovery (6.8-11.2%) was not significantly affected, although the amount of non-recovered faeces and total faeces showed significant differences. Duckweed diet and SCP resulted in the largest amounts of non-recovered and total faeces (199-210, 224-225 g dm kg(-1) feed dm). Compared with fishmeal diet (FMD), the WGD and SBE resulted in similar growth, but higher non-faecal N losses (471-495 vs. 416 g N kg(-1) N). Soybean meal diet, DWD and SCP resulted in lower growth but less non-faecal loss (409-450 g N kg(-1) N). The DWD and FMD had the highest N retention (480 g N kg(-1) N) compared with the other diets (431-451 g N kg(-1) N). Carbon retention, faecal and non-faecal losses and P retention were similar for all diets (302-358, 142-176 and 489-523g C kg(-1) C, 606-704 g P kg(-1) P). Phosphorus faecal loss was lower for all diets (329-381 g P kg(-1) P) than for the FMD (401 g P kg(-1) P)