Optical development, feeding dependency on light intensity and food colour preferences in seahorse, hippocampus barbouri

Nor Syahira Idayu Ismail (2023) Optical development, feeding dependency on light intensity and food colour preferences in seahorse, hippocampus barbouri. Masters thesis, Universiti Malaysia Sabah.

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Abstract

Seahorse Hippocampus barbouri is a species frequently involved in international trade due to its significant economic value and demand in traditional Chinese medicine (TCM), as curios, and in the aquarium trade. In the world of TCM, dried seahorses can cost as much as USD 1,200 per kilogram. Whereas, in the marine aquarium business, captive-bred live seahorses are sold for anywhere between USD 60-950 each, which is more expensive than wild-caught seahorses, which typically sell for USD 1-80 each. Aquaculture addresses overexploitation and global demand, but the main challenge is the low survival rate of pelagic-stage seahorses due to a lack of suitable food and improper feeding and culture techniques. Despite a decade of research, there's still limited knowledge, especially about early development and eye development crucial for their feeding. Seahorses rely on visual cues, such as light intensity, tank colour, and prey contrast. This study aims to fill the knowledge gap on early seahorse eye development and explore physical factors that help seahorses adjust and enhance visual abilities to improve feeding activity. In experiment 1, the optical development of seahorse H. barbouri at the early life stage in captivity was examined histologically. Aborted yolk-sac larvae 324 hours after spawning, were still alive and newly released juveniles (0 day after birth, 0 DAB) were sampled until juveniles reached benthic stages at 15 DAB. At yolk-sac larvae, the eyes are fully pigmented with retina formed in a distinguish layer and supplied with optic nerve. Whereas the pigment epithelium in the newborn juveniles shone under surface lighting, indicating the presence of reflective retinal tapetum (eyeshine). Interestingly, the presence of retinal tapetum in seahorse species was first documented in this study. The retina grew progressively in size until 15 DAB without changes in the retina structure. Experiment 2 investigated how different light intensity levels (2100 lux and 1400 lux) from fluorescent and light emitting diode (LED) sources influenced the feed intake, growth, and survival of H. barbouri seahorses in pelagic stage. A total of 16 seahorse/tank was used in triplicate for each treatment. At the end of the 15-day culture period, treatment under fluorescent 1400 lux was the most favourable for juvenile growth, survival and feed intake. Experiment 3 was conducted to determine the synergetic effects of tank background and food colouration on the feeding preferences of sub-adult seahorse H. barbouri (standard length, SL: 7.56±0.35 cm; wet weight, WW: 0.58±0.10 g). Nine seahorses were reared in triplicate tanks with red, blue and green backgrounds for two weeks with a stocking density of one seahorse/tank. Sergestid shrimp, Acetes sibogae (TL:1.00±0.05 cm), were used as food test, dyed with blue, green, red and yellow, whereas natural or non-dyed Acetes served as control. Sub-adult H. barbouri seahorses were presented with two different colours of Acetes simultaneously, with each combination lasting five seconds. Testing continued until the seahorses lost interest in the food colours combination. After about a two-hour break, testing of different colour combinations resumed randomly. Against all backgrounds, the first response was significantly biased toward natural white colour shrimp. This study demonstrated that sub-adult H. barbouri has colour preferences. Conclusively, this study fills the gap in our understanding of H. barbouri's eye development during their pelagic stages. A light intensity of 1400 lux from fluorescent light proved optimal for H. barbouri's feed intake, growth, and survival at this stage. When weaning sub-adult H. barbouri, offering frozen Acetes with natural colouring in tanks with red, blue, or green backgrounds can expedite the process due to the contrast created with the use of light colour against dark colour.

Item Type:	Thesis (Masters)
Keyword:	Seahorse, Hippocampus barbouri, Traditional Chinese medicine
Subjects:	S Agriculture > SH Aquaculture. Fisheries. Angling > SH1-691 Aquaculture. Fisheries. Angling > SH20.3-191 Aquaculture
Department:	INSTITUTE > Borneo Marine Research Institute
Depositing User:	DG MASNIAH AHMAD -
Date Deposited:	05 Sep 2024 10:00
Last Modified:	05 Sep 2024 10:00
URI:	https://eprints.ums.edu.my/id/eprint/40838

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