Research Paper to Read: (2012) Effects of photoperiod on reproduction of Siamese fighting fish Betta splendens

Source: Research Gate.

(1) Photoperiod of ratio of 16h light : 8h darkness (spring) and 12h light : 12h darkness (summer) yield optimum reproduction and growth.

Why this paper?
As we have limited space, all our Betta sp. breeding projects were done within an indoor environment. For observation and appreciation purpose, the breeding and growing tanks were equipped with typical T5 LED lights. In the past, we kept the light on for 24 hours because we want to maintain the growth of the aquatic plants. Little we realized, it just dawned to us that animals and plants should follow the natural photoperiods just like in the wild. This begs the question, what is the optimum photoperiods when breeding and keeping Betta sp. Hence, the relevant of reading and understanding this paper.

Material and methods
This research includes 30 matured pairs or 60 fishes of super delta strain. On average, the weight and length of male is 1.92±0.28g and 3.84±0.13cm and female is females 3.72±0.18 cm and 1.72±0.23 g. (Note that the female size is roughly the same as male and typically for breeding, the female size should be smaller). These fishes were hosted within a 2 litres jar.

The design of the experiments for 5 treatments and 6 replicates for each pair of fishes as follows:
(1) 8L:16D
(2) 12L:12D
(3) 16L:8D
(4) 20L:4D
(5) 24L:0D

The breeding conditions for the next 150 days or 5 months are:
(1) Fluorescent light of 60 cm with 200 watt around 500-lux controlled by analogue timer.
(2) Total water changes every two days.
(3) Feeding done twice daily using diet of 45% crude protein and 12% fat in light photoperiod.
(4) Water treatment conditions are: pH 6.9±0.3, dissolved oxygen >5.0 mg L,-1 and ammonia <0.1 mg. L-1. Water parameters are monitored weekly.

The graphs below shows that photoperiod of 16L:8D and 12L:12D shows the significant differences in frequency of spawn, eggs volumes, and fecundity. 24L:0D yields the worst performance of all the measurements.

Does long exposure to light stresses the fishes which affects the production of the spawn size? The result indicates that this may be the main reason. Long light exposure is not natural and does not simulate a natural photoperiod (12L:12D) in outdoor or in the wild. Therefore, extra care needed to control the photoperiod as close as possible following the nature.

Further Questions
(1) Can we obtain similar result if the design and experiment was done in the outdoor environment where the photoperiod was controlled by exposure to sunlight?
(2) What kind of exposure to sunlight is suitable enough? The general consensus among breeder is that you cannot expose the fishes to direct sunlight but within the shaded area.

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