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Nsangou Amidou KpoumieCorresponding author Department of Animal Sciences, University of Dschang, Cameroon
Zooplankton production and growth performance of post-larvae of common carp according to the level and frequency of fertilization with chicken droppings were studied between May and October 2017 at the IRAD pisciculture station in Foumban. To this end, two doses of hen droppings, namely 450 g/m3 (D450) and 600 g/m3 (D600), were each applied at two application frequencies (weekly (F2) and bimonthly (F1)). Thus, 1200 post-carp larvae were distributed in 12 identical concrete tanks (1.2m x 0.75m x 1m) each filled with 400 liters of water. The 2 doses applied at 2 frequencies were applied randomly in the 12 tanks in a complete random device comprising 3 treatments and 2 repetitions. Six days after fertilization, each tank was sown with zooplankton at a density of 7 individuals per liter (ind/l). The loading was carried out 12 days after fertilization at a density of 100 ind/m2. The results show that regardless of the dose and the frequency of droppings applied, the production of zooplankton was optimal 10 to 12 days after fertilization. Considering the growth performance, the tanks receiving the 600 g/m3 dose every 2 weeks presented the highest significant values (p <0.05). On the other hand, the survival rate (36% on average) was not significantly influenced (p˃0.05) by the dose and the frequency of fertilization. The 600 g/m3 dose applied every two weeks can be recommended for the rearing of post-larvae common carp.
Antarctic krill is an important component of the zooplankton production in the Southern Ocean and is a major food source for baleen whales. The role of commercial fishing and predation by whales on Krill abundance has been investigated here using the innovative ecosystem-based fishery management, EBFM which maintains the krill to whale food web ecosystem stability. The literature indicates the Krill fishery may have been overfished, so it was reduced to the current annual upper limit of 0.62 million tonnes for support other predators of krill, such as seals, penguins and flying sea birds. However, recent literature suggests a moderate reduction in krill catch in the Antarctic Peninsula area due to its importance for whale migration to temperate areas. The Peninsula area catch was estimated to be reduced by about 10% due to additional concerns about climate change effects on krill abundance in the Southern Ocean, reducing overall catch to 0.556 million tonnes, moderately higher than the maximum taken in 2022. Hence, the krill biomass fishing was reduced to allow for predation by baleen whales and other predators, giving a full ecosystem-based fishing mortality similar to that previously estimated to maintain krill production in the Southern Ocean.