A STUDY INTO THE VISUAL CAPABILITIES OF THE ZEBRA-SNOUTED SEA HORSE HIPPOCAMPUS BARBOURI THROUGH TARGETED HISTOLOGICAL EXAMINATIONS AND BEHAVIOURAL STUDIES

The eyes of six adult Hippocampus barbouri, which had been captive bred at The National Marine Aquarium (NMA) and died of natural causes, were dissected out and blocked out in resin for sectioning. For each eye, one section in ten was mounted onto a slide and cover-slipped ready for analysis. The parts of the eye that were of interest were the retina and optic nerve. There was only one type of photoreceptor found that were concluded to be rods. The measurements of these rods ranged from 25 to 35 µm in length and 3 to 5 µm in width with no retinal pattern. The retinal layers ranged in size from 1 to 60 µm. The retina of the entire adult H.barbouri used for histology appeared to be rippled, this is thought to increase light capture. The width of the optic nerve ranged from 250 to 320 µm and the length ranged from 350 to 380 µm. All three of the diameter size groups of axon are present in the H.barbouri optic nerve with the majority being the small size, types II and I. The approximate total number of axons for H.barbouri is 2184. After the histology analysis, a behavioural study was set up to measure feeding under different lighting conditions. Eight different conditions were created using different lighting intensities and colours. These were; Daylight (900 lux), Dark (7 lux), Bright light (13040 lux), Blue light (940 lux), Red light (600 lux), Yellow light (460 lux), Bright halide and black material (Bhbm) (660 iux), and Duli halide and black material (Dhbrn) (360 lux). The number of prey items consumed was recorded along with the number of times a prey item is missed. When under blue light the H.barbouri had the highest number of hits and when under red light the H.barbouri gave the highest number of misses. There was no significant difference between the feeding of H.barbouri at different intensities of white light except when there was no light at all. Finally a 3D reconstruction of the eye was made using the 3D Doctor Computer package.National Marine Aquarium, Plymout