Enhancing Swimbladder Inflation in Yellowtail Kingfish Larvae for Improved Production Growth

1. Lindsey Woolley Flinders University Supervisors: A/Prof. Jian Qin Dr Bennan Chen Wayne Hutchinson Improvements in swimbladder inflation in yellowtail kingfish (Seriola lalandi) larvae

2. Problem • Cleans Seas Tuna production > 1 million YTK fingerlings per year • Currently ̴ 10 % larval survival rates • High swimbladder malformations per production run 0-60 days post hatch (dph) Failed inflation = Decreased survivability in larval rearing

3. Introduction • Swimbladder internal gas-filled sac, contributes to the ability of a fish to maintain neutral buoyancy • Flexible-walled organ found dorsally below the notochord • Impermeable to gas: poorly vascularized and lined with a sheet of guanine crystals Swimbladder of a rudd (Scardiniuserythrophthalmus)

4. Swimbladder malformation • Failed initial inflation • Linked to abiotic factors • Abnormal development, liquid dilated swimbladder collapses with hypertrophy of epithelium • 7 dph larvae without swimbladder inflation

5. Why is swimbladder malformation detrimental? = reduced production performance • Decreased survival • higher mortality under stress • Delayed growth • fish with no functioning swimbladder are 20-30% smaller in weight than normal fry • Skeletal deformities • occurrence of lordosis (curvature of the 2nd and 3rd vertebrae) • Metabolic demands higher • abnormal larvae have buoyancy abnormalities • higher energy requirements to maintain normal swimming behaviour

6. Project objectives • Increase swimbladder inflation rates of YTK larvae (< 2 % malformation) • Determine body density and distribution of larvae in rearing tanks • Determine abiotic factors that promote optimum swimbladder inflation • Increase overall survival rates to 25 % by 2011

7. Research plan 1. Swimbladder and body density assessment • Develop a standardized protocol to assess swimbladder inflation • use of anaesthetics compromises swimbladder volume • Describe larval swimbladder development • morphology and histological assessments (0 - 10 dph) • Determine effect of swimbladder inflation on body density and larval distribution within rearing tanks • density and distribution studies

8. Research plan 2. Abiotic factors • Investigate effects of surface skimmers • Skimmers remove oil from water surface • Allow larvae to gulp air at the surface for initial inflation • Photoperiod • Natural vs. artificial (halogen) light • Various photoperiod light regimes • Temperature • 20 – 25 °C

9. Research plan 3. Commercial validation • Assess YTK swimbladder malformation in weaned larvae • CST Arno Bay Hatchery • 40 dph YTK • Determine consequences of YTK swimbladder malformation on grow-out • CST Arno Bay sea cages • Fingerling – juvenile (5 g - 500 g) • Validate findings with Southern bluefin tuna (SBT, Thunnusmaccoyii) larvae • Describe swimbladder development in SBT • Investigate effect of abiotic factors on swimbladder inflation rates

10. Results YTK swimbladder development 0 – 2 days post hatch • Forms as an envagination of the digestive tract • Lumen increases in size • Epithelium cells decrease in thickness to allow for dilation • Rete mirabile develops as fine capillaries • Lumen is liquid-filled at this stage

11. 3 – 5 days post hatch Critical period for swimbladder inflation • Inflation occurs within a discrete window between 3 – 5 dph • Liquid- filled bladder becomes inflated with air … ? process is still not understood properly • Gas gland develops at the anterior pole, composed of squamous epithelium • Rete mirabile increases in complexity – functions as a countercurrent exchanger

12. Post larval stage • Reared in hatchery (0 -40 dph) • 3.5 g • Reared in nursery (40 – 60 dph) • 3.5-5 g • Grow-out in sea cages • (>5 g) 8 dph larvae with inflated swimbladder 9 dph larvae with collapsed swimbladder 7 dph larvae with an inflated swimbladder

13. Fish with non-inflated swimbladders Fish with inflated swimbladders Body density change with growth An increase in bladder volume = larvae are less dense then their environment and rise to the surface Initial Inflation 2 dph liquid-filled Swimbladder Inflation failure = sinking death syndrome (10 – 15 dph) • Specific gravity • With inflation: 1.022 g cm-3 • Without inflation: 1.030 g cm-3 • MANOVA: P< 0.001

14. Commercial applications • Increase production of YTK larvae to a 25 % survival rate by 2011 • Increase the rate of swimbladder inflation, contributing to the overall increase in larval survival rates • Define a standard protocol for swimbladder assessment at 3 – 5 dph larvae • Define the range of abiotic factors that promote optimal swimbladder inflation • Compare the swimbladder development between YTK and SBT

15. Acknowledgements • Australian Seafood Cooperative Research Centre • “This work formed part of a project of the Australian Seafood Cooperative Research Centre, and received funds from the Australian Government’s CRCs Programme, the Fisheries R&D Corporation and other CRC Participants”. • Flinders University • A/Prof. Jian Qin • SARDI-Aquatic Sciences • Dr Bennan Chen • Wayne Hutchinson • Clean Sea Tuna Ltd. Arno Bay Hatchery • Mike Thomson • Alex Czypionka • Hatchery system images courtesy of Paul Skordas (SARDI Hatchery)