2009/733 Body buoyancy and distribution of fish larvae: Exploring the mechanism of mass mortality

By Lindsey Woolley


Technical challenges in larval fish rearing, especially the mass mortality in early stages, still remain an important impediment to aquaculture. The supply of high quality juveniles to grow-out is restricted by poor larval performance and low survival. Overcoming the technical and biological constraints is essential to the development of the finfish industry. Survival, growth and quality of fingerlings have improved over the past few years but new efforts are still needed to produce large predictable volumes

Low swimbladder inflation is a major cause of mass mortality in larval fish rearing, but mechanisms underlying swimbladder inflation are poorly understood. The aim of this thesis was to mainly use the larvae of  Yellowtail Kingfish (YTK) to understand the pattern of morphological development associated with body density change, examine the impact of abiotic factors on swimbladder inflation and explore the causality of mortality associated with distribution in the water column of culture tanks.

They found that the initial swimbladder inflation window for YTK occurs within a finite window between 3 and 5 days post hatch and this milestone is critical in preventing mortalities associated with sinking larvae. Poor survival is usually associated with low inflation rates which may be attributed to the inappropriate range of abiotic conditions. Initial swimbladder inflation was significantly affected by light source, with the highest inflation rate under artificial light. Fish growth was improved at the higher temperature and light intensity. Similarly, survival was significantly influenced by light intensity, with the highest survival at the high intensity, but not by dissolved oxygen. Low swimbladder inflation rates and the negative body buoyancy induced the high mortality rates. This study indicates that management strategies to maintain larvae within the water column and enhancement of swimbladder inflation rates are essential to improve survival rates in Southern Bluefin Tuna larvae.