Molariform teeth and gill rackers differentiation among cultured and wild Nile tilapia.
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The study was intended to characterize the molariform teeth and gill rakers development in farmed and wild Nile tilapia of comparable sizes. Two categories of farmed fish were considered in this study;1) the one fed on a sinking feed alone and 2) the other fed on a floating feed alone. The physical characteristics of the feeds including pellet dimensions, disintegration, sinking rate and bulk density were examined. These parameters were further explored and related to molariform and gill raker development among farmed Nile tilapia. The gill rakers and molariform teeth were dissected carefully from the fresh fish (n=100)) using a sharp knife. A micrometer microscope was used to measure; length of the gill arch, length of the filaments, and spacing of the filaments. Pellet dimension was determined by measuring the diameter and length of thirty pellets for each feed using a vernier calliper. The physical properties of the feeds varied significantly among the two feed types. The sinking feed showed the highest sinking rate (46.23 ±4.21cm/s), bulk density (42.21±3.24g/cm3) and pellet disintegration (32.21±2.54 minutes). Fish fed on the floating feed had more widely spaced gill rakers (38.21±2.24 mm), numerous gill rakers (43.21±3.14), longer and thinner filaments and a higher gill arch length (46.21±2.24mm) compared to the fish fed on the sinking feed. Fish fed on sinking feed had few, smaller and less spaced molariform teeth (32.23±2.21) compared to the fish fed on the floating feed. Fish fed on the both feeds had more widely spaced gill rakers ( 48.21±3.24 mm), numerous gill rakers( 45.11±3.14), longer and thinner filaments and a higher gill arch length ( 42.21±2.34) compared to the wild fish. To achieve sustainable development of commercial aquaculture feeds, there is need to improve the efficiency of feeding fish on feeds with standardized physical parameters (Pellet stability in water, sinking rate, bulk density and pellet dimensions) and the right chemical composition to maximize feed utilization.