Preliminary Results of Jade Perch Feed Trial

By Max Wingfield

Aquaculture Extension Officer

Please note that not all aspects of this trail can be reported on, at this stage, as the trial has only recently finished and much of the data collected has yet to be analysed.

Introduction

With the recent development of jade perch farming as a significant sector of the Queensland aquaculture industry, the AAQ has been actively encouraging research on the species.  There are a number of fundamental issues relating to fish husbandry and biology that need to be addressed in order to improve the efficiency of jade perch production.

One of the major issues identified by the AAQ is to establish some baseline information on jade perch dietary needs and to assess their performance using a range of existing aquaculture diets.  Therefore it was decided to conduct a feed trial to begin the process of answering some of these rudimentary feeding issues.  The research was undertaken by DPI staff at the Walkamin Freshwater Fisheries and Aquaculture Centre and was initiated in response to a request by the AAQ, who provided funding towards the study. 

The Experiment

The experiment was designed to assess fish performance in terms of growth rate, food conversion and fat deposition when utilising each of five diets (table 1).  The diets used in the trial were selected to provide baseline information on the ability of the fish to utilise a broad range of dietary formulations.  Four of the diets that were trialed were commercially available aquaculture feeds.  The fifth diet was a mixture of the other four diets and was included so that there was a fairly regular increment in the basic nutritional profile (protein, crude fat and energy) of the five experimental diets (table 1).

 

Table 1: Basic Nutritional profile of the Five Diets Used in the Experiment

Diet

Protein

      (%)

Crude Fat (%)

Energy (MJ/kg)

Cost ($/kg)

Excluding GST & Freight

1) Ridleys Redclaw  (pellet)

20

3

10

0.48

2) Mixed *1

27.4

5.4

11.7

0.70

3) Select Silver Perch (6mm)

32

9

13.5

0.94

4) Ridleys Native Fish (6mm)

45

10

14

1.15

5) Ridleys Barramundi (6mm)

50

12

18

1.35

 

*1 “Mixed” = 66.7% Ridleys Redclaw, 11.1% Select Silver Perch, 11.1% Ridleys Native Fish, 11.1% Ridleys Barramundi

The experiment was conducted over a three-month period from October 2001 to January 2002.  Fifteen, 600 litre, tanks were used in the experiment.  Each tank contained 10 fish with an average initial, individual, fish weight of 338g.  Three identical, indoor, semi-recirculating systems (17% water replacement per day) were used.  The three systems each consisted of five experimental tanks sharing a common biofilter.  This infrastructure allowed for the experiment to be conducted and analysed as a randomised block design.  The fish were fed to satiation during a 1-hour feeding period every evening.  Fish were anaesthetised, weighed and measured at one-month intervals.

Water quality was monitored on a weekly basis throughout the experiment and water temperatures were electronically recorded every hour.  All water quality parameters remained within a satisfactory range throughout the experiment and there were no major differences between treatments.  Average daily water temperatures started at approximately 26.5 °C in October, and rose to approximately 30 °C in January.

Results

All fish appeared to be in good health throughout the experiment and no mortalities occurred.  At this stage of data analysis, the major findings of the trial relate to growth rate, feed conversion, cost of diet and fat deposition.  Each of these aspects is discussed below.

Growth Rate

Significant growth was recorded for all diets (figure 1), with average weight gain for the redclaw, mixed, silver perch, native fish and barramundi diets being 152, 244, 281, 286 and 306 grams respectively.  Although the best growth rate was achieved on the barramundi diet, from a statistical perspective (p < 0.05), growth on the barramundi diet was not significantly different to the native fish diet or the silver perch diet.                     

Feed Conversion

Feed conversion ratios ranged significantly between the diets (figure 2), with the cheaper, less refined diets having much poorer feed conversion rates (FCRs) than the more refined diets (figure 2).  FCRs for the redclaw diet averaged approximately 3.5, the mixed diet averaged 2.5, while the three commercial fish diets were not significantly different from one another, averaging approximately 1.7.

It is interesting to note that the FCRs for all diets increased (less efficient conversion) as the experiment progressed (figure 2).  Such an increase in FCR is commonly observed in trials where fish have been held on restricted rations prior to the experiment and are then fed to satiation.  As the fish approach optimal condition, and fat reserves, their growth rate and feed intake often decrease whilst their metabolic requirements remain the same, thus resulting in lower feed conversion efficiency.  It is also possible that the nutritional quality of the diets may have deteriorated slightly over the course of the experiment, as all the feed was obtained just prior to the start of the experiment and then stored at 4 °C.

Note that feed consumption data for the redclaw diet is not available for the first month of the trial.  Feeding practices had to be refined in order to minimise wastage of this diet, as the redclaw diet, unlike the fish diets, 

was a sinking pressed  pellet that disintegrated relatively rapidly in water.                           

Feeding Cost

Another method of looking at the results is to calculate the cost of feed required to achieve 1kg of growth for each diet (this calculation is based on FCR and the cost of the feed).  The “feeding cost” results are shown in figure 3.  It must be emphasised that this is not an exercise in modelling production costs, which include many other factors.  Therefore this simple calculation does not indicate the overall economic merits of the various diets. 

It can be seen that both the crayfish and silver perch diets have the lowest feeding cost, at around $1.70 per kg of weight gain.  The feed cost of the mixed diet averaged $1.77 and the native fish and barramundi diets were $1.97 and $2.14 respectively.  As was the case with the FCRs (Figure 2), the feeding cost increased as the experiment progressed.

Fat Deposition

Despite the major differences in the nutritional profiles of the diets (figure 1), the amount of fat stored in the body cavity of the fish (expressed as percentage of visceral weight, ie fat, liver and digestive tract, to total body weight) averaged 16% and did not vary significantly between diets.  This is a very interesting result and confirms that jade perch are able to utilise the available fat and dietary energy sources extremely efficiently.  It also indicates that the fish are probably capable of converting dietary carbohydrates into lipids and fats.

Fatty Acid Analysis

Samples are to be sent away for laboratory analysis in order to determine whether diet affects the amount of fat stored in the flesh (fillets), or the proportion of omega-3 fatty acids.

Flesh Recovery

The three fish diets each averaged 41% flesh recovery (as a skinned boneless fillet), the mixed diet averaged 40% and the crayfish diet averaged 38%.  These differences, however, are not statistically significant.

Discussion

The results of this experiment are very encouraging and demonstrate that jade perch is a robust omnivore, capable of utilising diets of relatively low nutritional value with a high degree of efficiency.  The growth rates and FCRs obtained on the commercially produced fish diets compare favourably with other fish species that have been the focus of many years of nutritional studies.

It should be noted that this experiment was conducted in clear-water tanks.  Therefore, the fish did not have any opportunity to supplement their diets with the various food organisms that would occur naturally in ponds.  As such there may be some differences between the reported results and what may be achievable under particular pond culture conditions.  Furthermore, it must be stressed that none of the diets used in this experiment were formulated for use with jade perch.  Therefore their performance in this trial is in no way an indication of the overall quality of the diets, or of their suitability for their target species.  It is, however, fair to say that out of the five diets used in the experiment, the silver perch diet was the only diet that ranked favourably in terms of both growth rate and feed cost.  This result is not surprising given that the diet has been formulated to meet the needs of silver perch, which is a related omnivorous fish, and is likely to have relatively similar nutritional requirements to jade perch. 

Because this study is a preliminary study designed to evaluate a range of commercially available diets, it is impossible to make any specific comments on the exact nutritional balance that is required for jade perch.  More intensive studies with balanced reference diets would be necessary to determine an optimal dietary formulation for jade perch.  At this stage of industry development, however, the practical application of comprehensive nutritional studies is debatable, as feed manufacturers are unlikely to consider developing diets specifically tailored to the needs of jade perch until the industry is producing around 300 tonnes of fish annually.

The trial also shows that the amount of fat stored in the body cavity is not a simple function of the nutritional profile of the diet.  Therefore, if attempts are to be made to reduce the amount of body cavity fat, it is now apparent that industry and researchers will have to investigate other aspects of husbandry and feed management.  More information on fat utilisation and storage will be available when the fatty acid profiles of the flesh samples have been analysed.  It is, however, important to note that, even with the relatively high level of body cavity fat, the filleted flesh recovery of jade perch compared favourably with other cultured species.

Conclusion

It is now clear that jade perch is a hardy, omnivorous species, capable of achieving rapid growth rates on relatively inexpensive diets.  It is, therefore reasonable to assume that this species can be grown at a relatively low cost of production.  Furthermore, while jade perch do accumulate significant stores of body fat, they are well suited to filleting and provide a high recovery rate of flaky, white flesh. 

These findings support the position that jade perch is an exceptionally good species for aquaculture production.  It must, however, be stressed that jade perch farming is still a very new industry which faces many challenges and uncertainties.  In my opinion, the biggest current limitation to industry expansion is the lack of public awareness and mainstream market acceptance.  These marketing issues must be addressed and overcome in order to permit jade perch production to develop to a level correlating to its biological potential.

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