Comparative Biology of the Pink Shrimp, Penaeus notialis (Perez-Farfante), and Giant Tiger Shrimp, Penaeus monodon (Fabricius), in the Lagos Lagoon, Nigeria

Abstract

Eight hundred (800) specimens of pink shrimp, Penaeus notialis and giant tiger shrimp, Penaeus monodon collected from the Lagos Lagoon between February and May 2012.They examined with particular reference to size composition, growth pattern, distribution, sex, food and feeding habits. Some physico-chemical parameters Hydrogen – ion concentration; (pH), Dissolved oxygen; Salinity and Temperature of the environment were also studied. The air and surface water temperature ranged between 27.0^oC to 31.5^oC; mean value of 29.38±1.89 and 27^oC to 31^oC; mean 29.00±1.83 respectively. Hydrogen-ion concentration pH values ranged from 7.4 to 7.7. The salinity ranged between 15.6‰ to 20.1‰ with mean value of 17.78± 1.86 while the dissolved oxygen was between 3.9mg/l to 5.7mg/l; mean 4.65±0.82.The mean and standard deviation of carapace length of P. notialis and P. monodon specimens ranged from 2.583 ± 0.792 and 3.670 ± 1.255 while the mean and standard deviation of total length ranged from 8.898 ± 1.042 and 13.090 ± 1.326. The mean and standard deviation of total weight ranged from 4.237 ± 1.775 and 14.644 ± 4.060 respectively. The length-weight relationship reflected the common general increase in weight with increasing length. The shrimps exhibited a negative allometric growth. The condition factor (K) of the shrimps ranged from 0.51 to 0.69 and from 0.27 to 0.59 (male/female) in P. notialis, while in P. monodon it ranged from 0.46 to 0.76 and from 0.57 to 1.00 (male/female) respectively. The sex ratio obtained for P. notialis sample was 1:0.27 while in P. monodon a sex ratio of 1:1.53 were observed which showed a significant difference from the expected 1:1 ratio. The food and feeding habit of P. notialis and P. monodon from the Lagos Lagoon showed that both species fed majorly on crustaceans, diatoms, filament algae and plant materials. But, P. monodon fed more on food items in term of quantity than the P. notialis especially on crustaceans. It was observed that the plankton, crustaceans and plant materials were the most preferred food, Percentage of frequency of occurrence of filament algae are the same in both species.

Keywords: Penaeus notialis, Penaeus monodon, Growth, Food and Feeding, Lagos Lagoon.