Author: Jason Higham et al

Institution:  South Australian Research & Development Institute 

Title:  The effect of flow on growth in juvenile Greenlip Abalone, Haliotis laevigata (Donovan)

                                                                                                                                                                        

 

THE EFFECT OF FLOW ON GROWTH IN JUVENILE GREENLIP ABALONE, Haliotis laevigata (Donovan).

Jason Higham¹, Patrick Hone², Steve Clarke¹, Russell Baudinette³ and Michael Geddes³.

 

1: South Australian Research and Development Institute- Aquatic Sciences Centre.

2: Fisheries Research and Development Corporation.

3: Department of Zoology, University of Adelaide.

INTRODUCTION

Various factors such as temperature, salinity, dissolved oxygen concentration, pH, water quality, food availability, anatomy and behaviour are known to affect growth of juvenile greenlip abalone, Haliotis laevigata. Even though the aquaculture industry predominantly uses raceway designs for grow-out, the only assessment of the effect of flow rate on growth in juvenile greenlip abalone has been an undergraduate student project (Flemming et al., 1997). This is despite the evidence presented by Shepherd (1973) that flow rate is important in controlling the food consumption rate of this abalone species in the field. Shepherd observed that when exposed to flow, greenlip abalone adopt a distinctive feeding posture, whereby they raise the front of their shell and catch driftweed with their foot instead of grazing on benthic algae. The aim of this series of experiments was to assess statistically whether flow rate impacts upon growth, thereby determining if this difference is biologically meaningful.

METHODS

As an honours project (Higham, 1998), a series of growth experiments evaluating the effect of water flow was undertaken at SARDI Aquatic Sciences, West Beach. Juvenile greenlip abalone supplied by Southern Eyre Marine Farm, Louth Bay, South Australia, were subjected to different flow rates under simulated darkness, and their average growth rate determined from initial and final measures of length, width and wet weight.

In the first 40 day growth trial, 70 abalone (30.88 ± 0.16 mm in length) were confined to a 500mm section of each of nine commercial raceways, designed by SAABDEV, Port Lincoln, South Australia (Figure 1). The abalone were fed artificial food supplied by ADAM & AMOS ABALONE FOODS, Mount Barker, South Australia, at a rate of 2.8-2.9 % of their initial body weight daily while subjected to three flow rates; 2 L/min, 10 L/min and 20 L/min. Three replicates of each flow rate were used. In the second 40 day growth trial, 70 abalone (34.65 ± 0.26 mm in length) per raceway were once again subjected to the same flow rates but instead were fed 3.8-3.9 % of their initial body weight daily. For both of these trials, water was recycled by pumping water back to the header tanks following settlement of any particulate matter.

In the third 40 day growth trial, groups of 31 abalone (32.83 ± 0.40 mm in length) were subjected to nine evenly spaced, separate flow rates between 0.5 and 4.5 L/min while contained within an 800 mm section of each PVC guttering based raceway as used by Flemming et al. (1997). These flow rates were adopted in an attempt to examine the same 'velocities' used in the previous two commercial raceway trials. In this context, velocity refers to flow rate divided by cross sectional area. Abalone were fed 6.0-6.1 % of their initial body weight every second day and no replicate flow rates were used. No water was recycled from the raceways during the experiment. In all three growth trials, water height was set and maintained at 11 mm.

During the growth experiments conducted in commercial raceways, the space utilisation was also assessed by recording the distribution of abalone at 14:00 hrs each day. Average apparent food consumption of the abalone in each commercial raceway was also assessed.

RESULTS

In the trials, abalone were seen to adopt a distinctive feeding posture as documented by Shepherd (1973) (Figure 2). Under conditions of flow, abalone were observed to form two ‘hands’ with their foot and grasp food as it moved past, detected by contact with the epipodial tentacles. The first 40 day growth trial showed a depression in growth rate with increasing flow rate (Figure 3). This is directly contrasted by the second 40 day trial where growth rate is positively affected by increasing flow rate (Figure 4). The third growth trial illustrates that at this lower feeding ration and stocking density, growth rate is depressed at the highest and lowest flow rates but maximised at an intermediate flow rate of 2.5-3.0 L/min (Figure 8).

The space utilisation data shows a definite alteration in distribution with increasing flow. In the first 40 day experiment, the high and intermediate flow rate showed similar numbers of abalone forming aggregations (6-14% and 6-10% respectively), while the lowest flow rate shows a much smaller percentage of aggregations (2-4%)(Figure 5). The second growth experiment (with a higher feeding ration) showed the opposite to this with low flow rates exhibiting greater numbers forming aggregations (6-12%) as opposed to the higher (4-10%) and intermediate flow rate (1-6%) (Figure 6) (Aggregations refer to abalone stacking on top of one another). The horizontal distribution of abalone in the second 40 day period showed a similar trend for all flow rates in that the number of abalone decreases down the raceway (moving away from the inlet), with abundance being least at the centre and highest near the edges. The only difference between flow rates was the rate of the change in abalone density and area of raceway not utilised (Figure 7).

DISCUSSION

These experiments illustrate that growth rate is affected by flow rate. Although no experiments were performed to directly test how flow alters growth, the range of experiments carried out give an indication. The most likely explanation is due to a combination of flow interacting with the animals' ability to catch food and the removal of wastes facilitated by the action of water flowing through the mantle cavity. As flow rate increases, the removal of wastes from the internal cavity and around the abalone increases, preventing the localised build-up of detrimental wastes. This is balanced by the increased rate at which food moves past the animal with higher flow since time required by abalone to detect and catch food as it moves past them is constant. At the highest flow rate, abalone are only able to react quickly enough to catch food as it moves past them when surrounded by other individuals that trap food against their shell.

In the third growth trial, unlike the previous two experiments, food was not presented every day, but instead every second day, causing abalone to be without food for longer periods (due to flow removing food from the area around the abalone as in the first two trials). This is the likely explanation for the depression of growth rate at higher flow rates since average daily intake would be reduced and therefore energy available for growth, less. In light of these results, intermediate flows exhibit the best compromise in terms of space utilisation by abalone, and average growth rate.

Further work must still be performed to assess the movement of abalone subjected to different flow rates in a raceway based system and how this affects energy usage and acquisition together with experiments to more accurately assess the role of flow on the ability of abalone to catch food and how artificial food interacts with abalone when exposed to flow.

REFERENCES

Flemming, A., Hone, P. and Higham, J. (1997). The effect of water velocity on consumption and growth of greenlip abalone in tanks. Proceedings of the 4th Annual Abalone Aquaculture Workshop, July 1997, Port Fairy. (Eds P.W Hone and A. Flemming) (South Australian Research and Development Institute.)

Higham, J.S. (1998) The effect of different flow rates in Low volume culture tanks, on growth in juvenile greenlip abalone, Haliotis laevigata (Donovan). Unpublished Honours Thesis, University of Adelaide, South Australia.

Shepherd, S. A. (1973). Studies on Southern Australian Abalone (genus Haliotis) 1. Ecology of five sympatric species. Australian Journal of Marine and Freshwater Research 24, 217-57.

 

Figures 1 - 8
Click on figure for enlargement

Figure 1: Picture of commercial raceways showing experimental set-up as used in Experiments 1 & 2.







Figure 2: Picture illustrating distinctive feeding posture of juvenile greenlip abalone, Haliotis laevigata.



Figure 3: Average Specific Growth Rate of length (± SE) as a function of flow rate for Growth Experiment 1 (SAABDEV Tanks).

Figure 4: Average Specific Growth Rate of length (± SE) as a function of flow rate for Growth Experiment 2 (SAABDEV Tanks).




Figure 5: Average percentage of abalone participating in aggregations for each flow rate grouping during Growth Experiment 1.




Figure 6: Average percentage of abalone participating in aggregations for each flow rate grouping during Growth Experiment 2.




Figure 7: Average Specific Growth Rate of length (± SE) as a function of flow rate for Growth Experiment 3 (PVC guttering).












Figure 8: Graphical representation of distribution of abalone in SAABDEV Raceways on 10th Jan 1998.

The average growth rate per day in Experiments 1 and 2 for each parameter, together with their associated standard error.

 

Summary of average daily growth rate for length, width and weight (± 1 standard deviation.)

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