Improvement of formulated feeds and feeding management for redclaw aquaculture in Australia

Thobejane, Tubake Refiloe (2015) Improvement of formulated feeds and feeding management for redclaw aquaculture in Australia. Masters (Research) thesis, James Cook University.

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The redclaw crayfish Cherax quadricarinatus has high potential for aquaculture in Australia. However, the farming of the species in the country has not fulfilled early high expectations after initial fast expansion in the 1980s and 1990s, and in recent years, there has been a decline in redclaw aquaculture production since 2006. Among various major obstacles identified, problems associated with feeds and feeding have been a major cause of concern for redclaw farmers for years. In particular, currently the commercial feeds available for the redclaw farming industry in Australia have poor water stability and are only available in one size; and the industry lacks an efficient feeding management standard. A series of laboratory experiments were hence conducted to tackle these problems.

To determine a feeding regime that ensures maximum efficacy, a total of 72 juvenile redclaw (18 per treatment) were cultured individually (caged) within a recirculating system and were fed at four different feeding intervals (every day (D1), every second day (D2), every third day (D3) and every fourth day (D4)) with the same average daily ration of the commercial redclaw feed (i.e. average 5% body weight per day for all treatments). The redclaw were cultured for 20 weeks and data collected to assess their performance. The survival of juvenile redclaw increased with reduced feeding intervals ranging from 77.8% in the D4 treatment to 88.9% for the D1 and D2 treatments, with an intermediate 83.3% survival recorded for the D3 treatment. No significant effect of the different feeding intervals on the growth performance and feed conversion ratio (FCR) was detected. Hence, feeding every day appears unnecessary and a longer feeding interval of up to once every four days for this size range might be recommended, particularly considering that in pond culture situation, there are naturally grown supplemental feeds available to redclaw.

In the attempt to improve water stability of the commercial redclaw feed, six different binders (agar, alginate, carboxymethyl cellulose, carrageenan, polyvinyl alcohol and starch) were added at 3.0% dry weight, respectively to the crushed commercial redclaw diet and resultant new pellets compared for their water stability (i.e. physical form and dry matter lost (DML) after different durations of submergence in water), with the commercial redclaw diet as the control. Poor water stability of the commercial redclaw feed was confirmed as the feed totally disintegrated within 1 hour of immersion with a DML of 23.8%. All six binders significantly improved water stability but alginate was recommended as the overall best choice. The alginate was subsequently used as the binder incorporated at 5 concentrations (2.0%, 2.6%, 3.2%, 3.8%, and 4.4%) to evaluate the best inclusion level. The results showed that an inclusion level of 4.4% of alginate retained the best physical form of the pellet and produced the lowest DML overall of 16.2% after 24 hours immersion. The effect of pellet size (diameters: 1.0, 2.0, 3.0, 4.5, 5.0 and 7.0 mm) on water stability were also tested but appears to be a relatively minor factor.

The substantial reduction in wastage and the possibility of significantly improved water stability expected from the newly developed experimental diet (with alginate added at 4.4% as the binder) may lead to its less attractiveness to the redclaw and was tested by a feeding behavioural study on individual redclaw. To achieve this, behavioural experiments were designed to quantitatively assess and compare the feeding responses of redclaw to the introduction of the new pellets against the original commercial pellets, under identical feeding conditions.

The feeds used were both 4.5 mm in diameter and the results confirmed that the experimental diet remained water stable for a significantly longer time and as a result, had a significantly lower wastage level (5.0%) after 15 minutes of feeding compared to that of the commercial redclaw diet which crumbled quickly and with a significantly higher wastage (11.0%). It was further shown that in addition to its significantly improved water stability, the experimental feed was as attractive as the commercial diet to the redclaw as there was no significant difference in the mean 'time start feeding' as the redclaw responded to the introduction of both the experimental and commercial diets.

The final experiment examined the effects of pellet size on the feed wastage and feeding efficiency of three different sized redclaw using the experimental diet. The results showed clear evidence that using an inappropriate feed size led to significantly lower feeding efficacy and higher feed wastage and that the pellet size of 4.5 mm (the only size of commercial pellets available to redclaw farmers) were too big even for adult redclaw of individual weight of up to 50 g. Based on the results from this experiment, it was recommended that the most suitable pellet size for the juveniles (5 - 8 g), sub-adults (15 - 25 g) and adults (35 - 50 g) redclaw was 1.0, 2.0 and 3.0 mm, respectively.

This study has made several key findings for the improvement of feeding management and formulated feeds for redclaw crayfish farming. Feeding every day appears unnecessary and longer feeding intervals of up to once every four days are recommended for redclaw farmers to save on labour and other associated costs. The poor water stability of the currently available commercial redclaw feed in Australia can be substantially improved by incorporating 4.4% alginate of total diet dry weight as the binder. It is also recommended that instead of a single pellet size available at 4.5 mm only, the redclaw feed should be pelletised at 1.0 mm, 2.0 mm and 3.0 mm for juveniles, sub-adults and adult, respectively. These recommendations should enhance the productivity of the redclaw farming industry in Australia.

Item ID: 42316
Item Type: Thesis (Masters (Research))
Keywords: aquaculture; Australian red claw crayfish; Cherax quadricarinatus; farming; feeding; feeds; freshwater blueclaw crayfish; Queensland red claw; redclaw crayfish; tropical blue crayfish
Date Deposited: 21 Jan 2016 04:48
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070401 Aquaculture @ 50%
07 AGRICULTURAL AND VETERINARY SCIENCES > 0702 Animal Production > 070204 Animal Nutrition @ 50%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830101 Aquaculture Crustaceans (excl. Rock Lobster and Prawns) @ 100%
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