Kenan Engin

Ammonia and urea excretion rates of juvenile Australian short-finned eel (Anguilla australis australis) as influenced by dietary protein level

Abstract This study aimed to determine excretion rates of ammonia and urea of Australian short-finned elvers as influenced by varying dietary crude protein intake. Elvers (2.3±0.02 g) were fed diets containing dietary crude protein levels of 25% (P25), 35% (P35), 45% (P45) and 55% (P55) dry matter equivalent to 14.17, 19.24, 20.57 and 26.39 g CP/MJ, respectively (pairs of diets P25, P35 and P45, P55 were isoenergetic). Elvers were fed twice a day to a total of 6% BW/day and nitrogenous excretory products (ammonia- and urea-nitrogen) measured during the following 24 h and peak excretion rates occurred 4–8 h following both the morning and afternoon feed. Daily ammonia-nitrogen excretion was significantly (P

Ingredient apparent digestibility coefficients for the Australian short-finned eel ( Anguilla australis australis, Richardson)

Fish-meal is the most widely used protein source in commercial eel feeds and research evaluating alternative protein sources is lacking especially for species under current aquaculture development. This investigation was conducted to determine apparent digestibility coefficients of available plant and animal meals for the juvenile Australian short-finned eel (Anguilla australis australis Richardson). The suitability of a modified Guelph-type settlement faecal collector in eel digestibility studies was assessed. Animal by-product (meat; blood; poultry) and plant protein (soybean; canola; corn gluten; lupin; field pea) meals were mixed with a reference diet and marker (0.3:0.69:0.01) and the resultant test diets fed to the juvenile eels (3.15 plus or minus 0.42 g) at 5% BW/d. The reference diet and all the test diets were accepted and consumed at the fed ration. Apparent digestibility coefficients for crude protein (ADCCP) for all test ingredients were between 0.85 and 0.97. However, apparent digestibilities for dry matter (ADCDM) and energy (ADCkJ) were 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 extractives in the former plant proteins. There were significant (P<0.01) positive correlations between ADCDM and ADCkJ (r = +0.98), ADCDM and ADCCP (r = +0.62) and between ADCCP and ADCkJ (r = + 0.55). Similar results obtained for warm water species using similar faecal collection techniques and limited digestibility data from eels supported the suitability of the modification of the Guelph-type settlement collector system.

Growth and food utilization of the Australian short-finned eel, Anguilla australis australis (Richardson) given paired iso-energetic diets with increasing crude protein content

This study investigated the effects of 100 g/kg increments of crude protein (approx. 250 (P25) to 550 (P55) g/kg of crude protein) in paired iso-energetic diets on the growth performance of the juvenile Australian short-finned eel (1.83 (s.e. 0.01) g average wet weight). The highest growth response was obtained with treatment P45 followed by P35, P55 and P25. It appeared that food efficiency ratio (FER) increased with increasing crude protein content in low energy diets (treatments P25 and P35). However, 100 g/kg increase in dietary crude protein content (from 450 to 550 kg crude protein per kg diet) in high energy diets resulted in lower FER for treatment P55 than for the treatment P45. The protein efficiency ratio (PER, %) was higher in low protein:low energy diets (treatments P25 and P35) than that of high protein:high energy diets (treatments P45 and P55). The protein productive values (PPV, %) for treatments followed a similar trend to PER in this experiment. The lowest PPV was obtained by the treatment P55 and it was significantly different from that of the other three treatments. A proportional increase in dietary crude protein content in paired isoenergetic diets did not significantly change the whole body protein content. However, a small increase in whole body protein content with increasing dietary crude protein in each group was detected. In conclusion, the present study showed protein sparing effects of lipids and carbohydrates in the diets of the short-finned eel. Further studies specifically investigating the effects of dietary carbohydrate to lipid ratios at different protein levels would improve diet formulation and reduce nutrient impact in intensive recirculation systems.