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

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

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 (Scardinius erythrophthalmus)

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

Why is swimbladder malformation detrimental?  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 2 nd and 3 rd vertebrae)  Metabolic demands higher  abnormal larvae have buoyancy abnormalities  higher energy requirements to maintain normal swimming behaviour = reduced production performance

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

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

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

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 g)  Validate findings with Southern bluefin tuna (SBT, Thunnus maccoyii ) larvae  Describe swimbladder development in SBT  Investigate effect of abiotic factors on swimbladder inflation rates

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 Results YTK swimbladder development

3 – 5 days post hatch  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 Critical period for swimbladder inflation

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

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

Commercial applications  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 Increase production of YTK larvae to a 25 % survival rate by 2011

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)