Effect of feeding defatted canola on daily excretion of ammonical - nitrogen (NH₄-N) and ortho-phosphate (o-PO₄), in Channa punctatus (Bloch.)

M Jindal, S K Garg and N K Yadava

Department of Zoology and Aquaculture, CCS Haryana Agricultural University, Hisar 125 004 (Haryana)

mypshya@rediffmail.com

Abstract

To study the daily excretion patterns of wastes like ammonical nitrogen (NH₄-N) and ortho-phosphate (o-PO₄) fish were fed on 10 iso nitrogenous diets (D₁ to D₁₀) formulated by replacing fishmeal (FM) with defatted canola  at 4 inclusion levels (25, 50, 75 and 100g/kg) with and without supplementing the diets with a mineral premix and amino acids (MPA).

 

Studies have reveled that oxygen levels (DO) fluctuated between 4 to 5 mg/l and pH remained alkaline (7.5 to 7.9). Significantly (p<0.05) highest conc. of NH₄-N and o-PO₄ were observed in the water medium in which fish were fed on reference diets D₁ and D₆ containing FM as the main protein source. The excretion decreased on increasing the inclusion levels of defatted canola. Further, in the groups of fish fed on diets D₆ to D₁₀ the excretion of NH₄-N and o-PO₄ was lower than those observed in groups of fish where diets D₁ to D₅ were used indicating that incorporation of MPA reduces the excretion of NH₄-N and o-PO₄ in water medium. The peak time of excretion of NH₄-N was observed at the end of 6 hrs. of  post-feeding and of o-PO₄  was observed at the end of 8 hrs. of post-feeding.

Key words: Ammonical nitrogen, Channa punctatus, defatted canola, excretion, fishmeal, ortho-phosphate

Introduction

Proteins are the main source of nitrogen and essential amino acids and also the most expensive energy source (Pillay 1992).To maximize the nutrient utilization and minimize the solid and soluble waste load, it is essential to provide cultured fish with optimum level of protein (Cho 1993). Generally, nutrients absorbed in excess of requirement may be excreted as ammonia and urea (Beveridge and Phillips 1993). When food wastage is high and nitrogen retention and assimilation are poor, a major portion of nitrogen is added to the culture system, which may ultimately pollute the environment (Handy and Paxton 1993).

 

Fishmeal, which is considered as the best source of protein for fish is difficult to get in interior parts and even if it is available, it will be very costly To reduce feed cost and substitute of minerals and protein components of diets, materials of plant origin such as soybean, canola (rapeseed), cottonseed meal etc. to varying degrees were suggested by Hastings (1976),  Jackson et al (1982),  Viola et al (1982, 1983); Lall (1991 ), Kaushik (1992); Vielman et al (2000), Jindal (2001), Priyanka and Garg (2002), Jindal and Garg (2005), Robinson and Menghe (2007).

 

Rapeseed and mustard oil is primarily used for edible purposes, while the defatted meal is utilized as animal feed. Black and dark brown seed coat colour is of normal occurrence in rapeseed mustard. Further, canola (Brassica napus) is currently defined as having less than 2% erusic acid in the oil and less than 30 micromoles of the aliphatic glucosinolates per gram of oil free meal. Canola meal, has about 40% protein (on a dry matter, oil free basis) and a relatively well balanced amino-acid composition. Canola meal is a high protein feed ingredient of plant origin, however, it possesses some anti-nutritional compounds such as glycosides and tannins. Furthermore, protein in canola is surrounded by relatively indigestible carbohydrate, which cannot be broken down without the use of added enzymes (Buchman et al 1997).

 

Fish excrete phosphorus in soluble and particulate forms (Lall 1979, 1991 and Pillay 1992; Vielman et al 2000) The soluble fraction is called ortho phosphate (o-PO₄), is most available for plant growth (Bostrom et al 1988). However the main loading of phosphorus to the environment was reported to be via faecal pellets (Pillay 1992, Kibria et al 1996, 1998).

 

The main product excreted by teleosts fish is total ammonia nitrogen (TAN), which is formed in the lever and excreted across the gills .About 80-90% of nitrogen loss from fish is through gill excretion and the faecal nitrogen loss accounts for 10-20% .Nitrogen is also lost through uneaten feed or dust (Kibria et al  1996, 1998).(Figure 1). 

Therefore, there is a need to search alternate protein sources, that may also reduces the input of nitrogen and phosphorus into the environment.

 

Material and methods 

Specimens of Channa punctatus were obtained from fish dealers of Hisar. Specimens with mean body weight (8.0 to 15.0 g) were used in the studies. Fish were placed in the transparent glass aquaria (60X30X30 cm) kept in the laboratory where the temperature was maintained at 25±1⁰C and the lighting scheduled at 12h of light alternating with 12h of darkness. The fish were acclimatized for a minimum of 7 days prior to the initiation of experimental treatments. The water was renewed daily with chlorine free water.

 

Canola was used as the main protein source. It was defattened to remove antinutritional compounds prior to the preparation of experimental diets (Jindal 2001, Garg et al 2002).

 

Groundnut oil cake, Rice bran, fishmeal and defatted canola were finely ground to pass through 0.5 mm sieve. All the ingredients were mixed according to Table 1 and dough was made using distilled water.

Thereafter, the dough was passed to a mechanical palletizer to obtain pellets (0.5 mm thick) which were dried in an oven and used in the studies for 45 days. The proximate composition of all the 10 diets is presented in Table 2.

On the last day of experiment offer the same feed to the fish in sufficient quantity so that the same is consumed, wait for 2 hours. Maintain a fixed level of water in each aquarium (say 30-40 L). Remove the excess of feed. Start collecting water samples from each aquarium in replicate of 2 for the determination of ammonical nitrogen (NH₄-N) and ortho-phosphate (o-PO₄) following APHA (1998) to see the influence of compounded feeds on pollution status of receiving water in the aquaria.

 

Calculate the excretory levels of NH₄-N and o-PO₄ in treated water as follows: 

NH₄-N excretion                     =          NH₄-N (mg l^-1) in aquarium water

(mg/100g BW of fish)                           Fish weight (mg) per L of water

  

o-PO₄ excretion                      =          o-PO₄ (mg l^-1) in aquarium water

(mg/100g BW of fish)                          Fish weight (mg) per L of water

 

Result and discussion 

The oxygen levels (DO) fluctuated between 4-5 mg/l and pH remained alkaline (7.5 to 7.9). Significantly (p< 0.05) highest conc. of NH₄-N and o-PO₄ were observed in the water medium in which fish were fed on reference diets FM100 and FM-M containing FM as the main protein sources (Table 3).

 

The excretion decreased on increasing the inclusion levels of defatted canola.

This is because the fish can digest plant proteins much more easier than animal proteins (Deepak and Garg 2003, Priyanka and Garg 2002, Jindal 2001, Kalla and Garg 2004)

 

Further in the groups of fish fed on diets FM-M to DC100-AAM,  the excretion of NH₄-N and o-PO₄ was lower than those observed in groups of fish where diets FM100 to DC100 were used indicating that incorporation of MPA reduces the excretion of NH₄-N and o-PO₄ in water medium (Table -3). These results are in agreement with those of Viola and Lahav (1993). According to them the calculated amounts of excreted (not retained) nitrogen per kg gain was reduced by 20% in the lysine supplemented feeds, as compared to the 30% protein feed. Concomitantly, calculated phosphorus excretion per kg gain was also decreased approximately by 100%.

 

Water samples were analysed for 16 hrs at 2 hr interval of post-feeding revealed peaks in NH₄-N and o-PO₄ excretion (Figure 2 and Figure 3).

 

The peak time of excretion of NH₄-N in groups of fish fed on diets FM100, DC25 and DC50 were observed at the end of 8 hrs. of  post feeding but in groups of fish fed on diet DC75 and DC100 the peak time of excretion of NH₄-N was slightly earlier i.e. at the end of 6 hrs. of post-feeding (Figure 2 A). 

In the groups of fish fed on diets FM-M to DC100-AAM supplemented with MPA, the excretion of NH₄-N was lower than those observed in groups of fish fed on diets FM100 to DC100 But the pattern of excretion of NH₄-N was same as for groups of fish fed on diets FM100 to DC100 (Figure 2 B).

 

The peak time of excretion of o-PO₄ in the groups of fish fed on the diets FM100 to DC100 were observed at the end of 8 hrs. of post-feeding (Figure 3 A), whereas  in the groups of fish fed on diets FM-M  to DC100-AAM supplemented with MPA, the excretion of o-PO₄ was lower than those observed in the groups of fish fed on diet FM100 to DC100 But the pattern of excretion of o-PO₄ was same as for the groups of fish fed on diets FM100 to DC100. But  the pattern of excretion of o-PO₄ was same as  for the groups of fish fed on the diets FM100 to DC100 (Figure 3  B).

These results are in agreement with those of Kaushik and Gomes 1998, Kaushik and Cowey, 1991; Van Weerd et al 1993, Jindal  2001, Priyanka and Garg  2002, Kalla and Garg 2004, Jindal and  Garg 2005, who reported ammonia and o-PO₄ excretion peaks between 7-9 hrs of  post feeding.

 

The differences between the present data and those of others on the peak in ammonia and phosphorus excretion may be attributed to the facilities used by different authors (e.g. the size of holding tanks and the prevailing environmental and rearing conditions). Perhaps it also depends on the species under investigation.

 

Conclusions 

• The determination of nutrient budgets and daily patterns of waste excretion in aquaculture is important for evaluating the potential waste load of fish farming effluents (Cowey and Cho 1991). This aspect of intensive fish farming is becoming increasingly important and is receiving much attention (Rosenthal et al 1993).

  
  

• The decrease in NH₄-N and o-PO₄ excretion in receiving water with the use of protein of plant origin in feed has important implications on the management of highly intensive farming system. Since the present studies are the initial attempt in this direction, more elaborate work will, therefore, determine the range of applicability.

 

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