Linking larval feeding behaviour with the morphology and spectral sensitivity of the visual system in southern bluefin tuna and yellowtail kingfish larvae
Hilder, P and Battaglene, S and Hart, NS and Collin, SP and Cobcroft, JM, Linking larval feeding behaviour with the morphology and spectral sensitivity of the visual system in southern bluefin tuna and yellowtail kingfish larvae, World Aquaculture Adelaide 2014, 7-11 June 2014, Adelaide, South Australia (2014) [Conference Extract]
The visual development of Southern Bluefin Tuna, Thunnus maccoyii, and Yellowtail Kingfish, Seriola lalandi, larvae was investigated to identify ontogenetic changes and species-specific retinal adaptations that have implications for their culture requirements. The study included a histological examination of retinal anatomy, microspectrophotometry of retinal photoreceptors and behavioural analysis of feeding performance. As seen in many first-feeding fish larvae, T. maccoyii and S. lalandi possessed only single cone photoreceptors and had similar maximum theoretical visual acuities (1.2 ± 0.10 and 1.1 ± 0.10, respectively). Rods, which are associated with low light (scotopic) sensitivity, and twin cones, which are associated with bright-light (photopic) sensitivity, were present in the retina of T. maccoyii and S. lalandi by 21 days post-hatching (dph) with a cone mosaic pattern observed in T. maccoyii at 30 dph and in S. lalandi at 21 dph. T. maccoyii developed a high cone cell density region in the ventral retina, and retinal pigment epithelium (RPE) migration prior to the occurrence of rods. Early migration of the RPE suggests the need for retinal "shading" of the light sensitive pigments during early development. Microspectrophotometry showed that T. maccoyii had twin cone visual pigments maximally sensitive to light in the blue-green part of the spectrum (λmax values of 494 nm, 507 nm and 524 nm), and behavioural experiments showed they fed preferentially at these wavelengths. In contrast, S. lalandi, displayed high rod density in the dorsal retinal region and spectral sensitivity of the twin cones in the green spectral regions (λmax 504 nm and 519 nm) with single cones also displaying violet sensitivity (λmax 415 nm). Behavioural feeding experiments showed that S. lalandi had improved feeding under red light. The light environment is of paramount importance to T. maccoyii and S. lalandi larvae, although both species exhibit very different light requirements and visual capabilities, which have important culture implications. T. maccoyii display retinal and behavioural adaptations to life and feeding in low light environments and the use of low-light intensity illumination during the first two weeks of culture has the potential to dramatically improve larval feeding and survival. In contrast, S. lalandi larvae display retinal and behavioural adaptations to life in bright light environments.