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Protein nutrition in the juvenile Australian short-finned eel (Anguilla australis australis Richardson)


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Engin, Kenan 2001 , 'Protein nutrition in the juvenile Australian short-finned eel (Anguilla australis australis Richardson)', PhD thesis, University of Tasmania.

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Little is known about the nutrition of the Australian short-finned eel,
Anguilla.australis.australis (Richardson) although it is considered as a prime
candidate for inland aquaculture in Australia. This study provides information about
the protein metabolism of the juvenile Australian short-finned eel. The efficiency of
partitioning dietary protein into growth is closely related to the amount of nonprotein
energy yielding substrates and the quality of protein (the availability and
balance of amino acids) sources provided in the diet. The measurement of
nitrogenous excretion can also give an insight into the nitrogen balance of fish and
partly define the success of a particular nutritional regimen. Therefore, this study
aimed at measuring the growth, growth efficiency and nitrogenous excretion of the
juvenile Australian short-finned eel fed over a range of dietary protein:energy ratios
and with selected Australian plant and animal proteins. Since the maximum protein growth will occur over a narrow range of dietary
protein:energy ratios, the effects of increasing dietary crude protein contents at two
different energy levels on the growth and growth efficiency were measured. A 10 %
increase in dietary crude protein (from 25 to 35 %) in low protein:high non-protein
energy diets positively affected weight gain whereas significantly (P <0.05) reduced
weight gain was observed for a 10 % crude protein increase (from 45 to 55 %) in
high protein:low non-protein energy diets. The whole body crude protein content
was not affected by diet but the whole body crude lipid content decreased with the
10 % crude protein increase at each energy level. This study indicated a proteinsparing
effect of non-protein energy sources in the diets of short-finned elvers. A
lipid to carbohydrate ratio of 0.9 appeared to be needed for the maximum growth.
The optimum dietary digestible crude protein (DCP):digestible energy (MJ DE)
requirement of the short-finned elvers was investigated with 7.5 % crude protein
increments (from 25 to 55 % of the diets) in iso-energetic diets. The optimum dietary
digestible crude protein was estimated as dietary percentage (% CP DM) and as a
dietary digestible crude protein:digestible energy ratio (g DCP/MJ DE) using total
weight gain (g). Second order polynomial (quadratic) and 5-SKM (five parameter
saturation kinetics) models were chosen for the estimation of the optimum dietary digestible crude protein. Two models gave similar results estimating the optimum
dietary digestible crude protein as 43.0 % CP DM (±3.5) (r2 = 0.79; F=9.2157;
P=0.021) and 41 % CP DM (r2=0.77) or as 24.5 g.DCP/MJ DE (±1.7) (r2=0.83;
F=12.0573; P=0.012) and 23.5 g DCP/MJ DE (r2=0.75) respectively. Whole body
crude protein and lipid contents tended to increase with increasing dietary crude
protein in this experiment.
Nitrogen losses are primarily through faeces and metabolic excretion and largely
influenced by dietary composition. Increasing protein content at two energy levels
caused peak nitrogenous excretion rates 4-8 h following both the morning and
afternoon feed. Daily ammonia-nitrogen excretion was significantly (P<0.05) higher
on high protein:low non-protein energy diet (P55) compared to the P35 and P45
diets. Increasing dietary crude protein intake resulted in increasing ammonia-
(y=0.022x+0.058; n=12; ?=0.88; P<0.001) and urea-nitrogen (y=0.0044x+0.426;
n=12; r2=0.55; P<0.05) excretion in treatments. The proportional increase in ureanitrogen
excretion to total nitrogenous excretion with increasing dietary non-protein
energy sources also indicated that urea-nitrogen excretion in the Australian shortfirmed
eel could be more responsive to nutritional variables. Fish meal is an expensive component of fish feeds and replacement of it with
alternative protein sources without compromising the growth rate has been a priority
in aquaculture nutrition research. Apparent digestibility coefficients were measured
in order to assess the suitability of selected Australian plant and animal protein
sources for fish meal replacement. Apparent crude protein digestibility was high for
the selected Australian plant proteins and animal by-products. However, dry matter
and energy digestibilities were found to be significantly (P<0.0001) higher for
animal by-products than for plant proteins except for corn gluten meal. This was
explained by the higher content of nitrogen free extract (NFE) in all the plant
proteins except corn gluten meal. A final experiment was conducted to test the
effects of fish meal replacement with corn gluten meal, meat meal, lupin meal and
soy bean meal in diets using the optimum DCP/MJ DE ratio on growth, growth
efficiencies and nitrogenous excretion by the Australian short-finned elvers by
formulating the diets according to the optimum DCP/MJ DE ratio and ADC values
determined in the present study.
This study primarily showed better dietary protein retention efficiencies when
juvenile Australian short-finned eel were fed low protein:high non-protein energy
diets and established the optimum DCP/MJ DE requirement of this species for
maximum growth. The establishment of the optimum protein:energy ratio and
identification of highly digestible alternative protein sources provides a basis for
decreasing nitrogenous waste production, maximising protein retention and better
eel culture practises in Australia generally.

Item Type: Thesis - PhD
Authors/Creators:Engin, Kenan
Keywords: Anguilla australis australis, Eels, Eels
Copyright Holders: The Author
Additional Information:

Thesis (PhD)--University of Tasmania, 2001. Includes bibliographical references

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