Based on the fact that Artemia are sensitive to light the current experiment was conducted to observe the behavior when Artemia are exposed to varying intensities of light, believing that the fish would prefer darker portions of a basin. However, our experimental data failed to reject the null hypothesis that the species do not have a preference for light, although observable, but not statistically significant specificity for the shaded area was observed in the first trial. In the first trial, the color of the basin was white, which created a doubt that probably the light which was being delivered form a 100W bulb placed 16 cm away was being scattered within the basin evenly and merely covering the lid for semi covered and blocked area was not preventing its scattering within the basin. Accordingly a darker basin was used in the subsequent trials with the ambient room light as the source of light instead of the bulb. However, this alternative arrangement failed to provide the expected result altogether.
The first trial in which 17 Artemia were used, 18 replicates of the 2 minute observation by three members of the group each showed that the lowest intensity of 313 Lux, which was the darkest section of the basin was preferred by the majority of the organisms (10), while 2 preferred the semi dark area (530 Lux) and 5 stayed in the highest light intensity area (760 Lux). However, when the data were compared using the Chi-Square test, the calculated value of 5.76 failed to exceed the pre standardized critical chi-square value of 5.99, thereby rejecting our alternative hypothesis. The subsequent trails totally failed to generate any more data to substantiate our claim of the organisms preferring shaded area although changes were made in the experimental design to provide the organisms a more natural environment by using natural light and a dark green basin to prevent the scattering of light and its equalization in the three sections of the basin. In Trial 2, where 18 organisms were used, each section of the basin attracted 6 organisms each, giving a chi-square value of 0 (zero), which was definitely nowhere near the critical chi-square value of 5.99. Our experiment therefore failed to reject the Null Hypothesis.
Every living species on the planet thrives in particular habitats congenial to their life requirements and processes. This is the reason that only particular types of plants and animals are found in different locations around the world. Temperature and light variations have been found to affect intensity of other aquatic organisms as well (Wong & Benzie 107). Animals are adapted to specific habitats too and Artemia sp. or brine shrimp, a local variety of arthropods, found in ponds and lakes is a popular model for studying habitat in the laboratory environment (Haag et al 284). Aquatic animals in particular have specific habitat requirements as the water salinity, temperature, intensity of light and availability of prey are essential prerequisites for their survival. This is the reason for different species of fish living in fresh water and shallow ponds and others in running rivers and deep oceans. Artemia franciscana, belonging to Phylum Arthropoda in particular, has been claimed to prefer a habitat where light is poor as it has prominent eyes without any protective anatomical feature which could make the species sensitive to light (Fox).
Although our results are towards the contrary, past studies suggest that the Artemia species have swarming patterns which show that they have specific preference for darker areas and they thrive only in water bodies in which requirements of specific salinity levels, temperature and light regimes are present (Gulbrandsen 659). Moreover Artemia species require very specific habitat requirements as far as ionic content or salinity level of the water bodies in which they thrive are concerned (Camargo et al 1). This may be difficult to reproduce in the laboratory. Although in our trials, care was taken to maintain temperature and identical salinity levels in all replicates of the trials so as not to allow them to act as confounding factors in the results, but our attempts were crude as the size of the basin, light and heat from the bulb might have restricted the movement of the organisms. Moreover all organisms were not of the same size and chosen randomly which might have confounded the results further. In addition as the experiments allowed an acclimatization period of just 30 seconds, it might have been too less for a genuine movement of the organisms to have taken place according to preference for darker spots. Moreover the short observation period of two minutes could be too less and recording of data is also subject to human error. In my opinion, if a properly designed, compartmentalized box is used where there are no chances of light scattering into the other, and if a longer duration of acclimatization period is permitted i.e. for hours or at least a day, the results could have been different. Scope for human error can be eliminated by using a video camera to record the movement of organisms in carefully designed equipment which provides scope for swarming to the Artemia organisms. The recordings can then be analyzed by modern software and statistical tools to identify the tendency of Artemia organisms as far as preference for light or dark areas are concerned.
In a similar study conducted on captive tench fish, it was observed that the fish under blue or white light were significantly less active during the photophase than those under red or no light (Owen et al 376). Light color spectrum, intensity and photoperiod are vital variations which influence fish growth as has been ascertained in another study which claims it affects the hormonal profile of the aquatic organisms as well (Boeuf & Bail 129). Another study investigating the influence of photoperiod on the growth and survival of Arctic Char, a type of fish determined that fish exposed to continuous light and food showed lower cumulative mortality (Burke 344).
Although our experiment failed to demonstrate the tendency of the Artemia sp. to prefer darker areas in the basin, the failure to do so can be attributed to the experimental design as it was too elementary. Other researchers in advanced laboratories while conducting extended field experiments have proven that light and other factors do affect aquatic organisms’ behavior as proved by (Owen at al 376), (Burke 344) and (Boeuf & Bail 129).
References
Boeuf, Giles & Bail Pierre-Yves Le “Does light have an influence on fish growth?” Aquaculture 177 (1- 4) (1999) 129-152
Burke, M G, Kirk, M R, MacBeth, N A et al “Influence of Photoperiod and Feed Delivery On Growth and Survival of First-Feeding Arctic Char” North American Journal of Aquaculture 67 (2005) 344-350
Camargo William N, Duran Gabriel C, Rada Orlando C et al “Determination of biological and physicochemical parameters of Artemia franciscana strains in hypersaline environments for aquaculture in the Colombian Caribbean” Saline Systems 1 (9) (2005) 1-9
Fox, Richard “Invertebrate Anatomy Online, Artemia franciscana” 2006. Web.
Gulbrandsen, Jon “Artemia Swarming—Mechanisms and Suggested Reasons”Journal of Plankton Research 23 (1) (2001) 659-669. Web.
Haag, Maggie, McBain, Louise & Glider, Bill “Habitat preferences of Artemia francisca” Tested Studies for Laboratory Teaching” 28 (2006) 284-294. Web.
Owen, Matthew A G, Davies, Simon J & Sloman, Katherine A “Light colour influences the behavior and stress physiology of captive tench (Tinca tinca)” Reviews in Fish Biology and Fisheries 20 (3) (2009) 375-380
Wong, J M & Benzie, J A H “The effects of temperature, Artemia enrichment, stocking density and light on the growth of juvenile seahorses, Hippocampus whitei (Bleeker, 1855), from Australia” Aquaculture, 228 (1-4) (2003) 107-121