Response of fish larvae to light intensity – Light is an external factor and ecological importance, including the color spectrum, intensity and photoperiod. Light very specific characteristics in aquatic environments and are very varied in nature. Minimum light intensity threshold required for the development and growth of fish larvae.
In the dark lighting conditions, the larvae tend to move to spread in search of prey. Thus requiring higher energy. High metabolic activity that requires large energy so that the rate of absorption of the yolk becomes faster.
Larval fish on the first day after hatching did not reveal any lighting pigment in the eye and very little visual differentiation. On the third day of the retinal pigment with a storied and vision has grown cells. Then on the fifth day of the optic nerve and the cone (cone-shaped cells in the retina) has grown.
RESPONSE OF FISH LARVAE TO LIGHT INTENSITY
The intensity can be varied, for example between 50 and 150 lux for fish Sparus auratus. However, some species can grow and thrive in very low light intensity is as in some species of pelagic fish larvae, while snapper (Morone saxatilis).
By the time the larvae generally live in estuaries with murky water. Juvenile herring Clupea harengus, swim faster and survive when moving into the dark waters.
When the larvae transform into juveniles, the rods (rod-shaped cells in the retina) has been formed. Photoreceptor cones and rods is an active work and sensitive to dark and bright light. Cone works when light conditions, while rods work in dark conditions / vague. With the development of adaptation to darkness and light, the young fish (juvenile) is easy to catch prey. Successful predation activity will support the growth of juvenile.
Some fish larvae still undeveloped organs are perfect eyesight so little differentiation to distinguish light and dark. On the pro larval condition, light is needed for stimulus coloring (pigmentation) in the organs of sight and color of the body, an important event in the early growth and development of the larvae.
In general, longer exposure time affects the speed of larval development. The presence or absence of light can give the effect of different activities on fish larvae. The movement of larval activity will affect the rate of absorption of the yolk when larvae develop from larvae to post-larvae pro. The efficiency of yolk absorption rate may occur as a result of low larval activity, so the yolk more absorbed for growth.
The level of light intensity required to optimize the growth of the larvae. Light intensity 600 – 1300 lx can increase the growth in fish seabream, while snapper larvae develop optimally at 600 lx. In other species, the optimum level is lower as the atlantic halibut, the best growth at 1-10 lx. Besides, there are some fish that are sensitive to high light intensity.
This can be seen in the Southern flounder fish (paralichtis lethogstigma) is tested in the range of 340 – 1600lx and no effect on the growth and metamorphosis, the same species are also found differences in post pigementasi larval metamorphosis
Event gathering movement of fish larvae under the light can be distinguished as a direct event that the fish attracted by the light assembly and indirect events namely because there is no light, the plankton and small fish congregate then small fish congregate then the fish in question come together with the goal of feeding (foraging).
Carp larvae easier to get their feed when there is light as evidenced by the amount of feed most commonly found in the stomach carp larvae during daytime or no light. Artemia is fototaksis positive and tend to huddle closer to the light source. This will facilitate the fish in the catch Artemia larvae as prey.
Variations in growth can also be explained by the activity of larvae prey, and very dependent on visual development of larvae. Low light intensities are needed to develop normal hunting activities.
Sea bream larvae prefer dim light with a survival rate and feed efficiency were higher than those in bright light. Based on the average value of the survival rate reached the temperature of 28 ? C is the best temperature for larval life