Does culture in the darkness effect retina morphology of Sepia officinalis?

Abstract

In Sepia officinalis there was no significant difference (P = 0.241) for the eye diameter in terms of body length. The body length was significantly longer in cuttlefish reared in the dark treatment (P = 0.029). This could be due to photoperiod regulating the release of growth hormones. The outer segment is similar in both treatments containing small compacted rhabdomeres elongating towards the inner segment. The dark retina has a thicker outer segment than the light, which could be an adaptation increasing the probability for photon capture by the rhabdomeres. Rhabdomeres vary little between treatments in comparison to vesicle cells and myeloid bodies. Rhabdomeres contract during illumination and elongate in the dark. The presence of myeloid bodies has been noted in the inner segment of the dark retina only. Myeloid bodies are said to transform into vesicle cells in the outer segment. A connection between pigment and vesicles has been suggested, however further research needs to be conducted on this area to determine their relation. Within the retina most of the variation occurred in the inner segment between treatments. The inner segment is thicker in the retina of the light sample which could be due to the need for photoproduct to synthesize rhodopsin under illumination. One of the biggest obstacles to overcome was achieving accurate orientation within the section of the sample. It is inconclusive whether the variation seen within the retina is due to the effect of darkness, due to the small sample size tested.