A comparative study of the effects of pelleted and extruded feed on growth, financial revenue and nutrient loading of Nile tilapia (Oreochromis niloticus L.) cage culture in a lacustrine environment

Abstract

We compared the benefits of using extruded feed (EF), against pelleted feed (PF) to guide cage culture investments in Great Lakes. Three out of six cages in the same farm had fish that were fed EF and the other half, belonging to a different farm had fish that were fed PF. The diets were similar in crude protein, lipid and energy content. However, the fiber content in PF was 4 times higher than that of EF. The fish fed on EF grew better (438.0 ± 7.4 g) than the fish fed on PF (220.8 ± 2.9 g). The cost of production for EF was about 26% lower than for PF, primarily because of better feed utilization. The load of P and N for PF diet was 59% and 29% higher, respectively, than when EF was used.Therefore, EF feed delivered better economic gains with lower environmental impact than PF feed. KEYWORDS:Cage culture; Nile tilapia (Oreochromis niloticus); cost of production; market channels; pellet stability; nutrient load. have only one production cycle per year, since turnover in the lake, occurring between August and October, may cause heavy mortalities (KMFRI 2016). The preferred market size of Nile tilapia around the L. Victoria basin is >400 g, with sales prices per kilogram of fish varying between market sections (KMAP 2016).As is common practice in Africa, most of the cage fish production is bought by agents who transport the fish, chilled, to retailers in major cities (KMAP 2016; Awuor et al. 2019). Many farmers prefer this route to market because the agents pay cash immediately. A second sales channel is through wholesalers who resell the fish to retailers and/or directly to consumers at the local markets. Here, the wholesaler pays for the fish up to a week later. Finally, a small fraction of the production is bought directly by consumers at the landing site. The farmgate price for tilapia in sub-Saharan Africa is relatively low, due to the limited purchasing power of the local buyers and because of competition with cheaper frozen tilapia imported from China (Awuor et al. 2019). Since there is little direct contact between farmers and consumers the price is determined primarily by the intermediaries. As a result, profit margins of fish farms are narrow. Globally, aquaculture practices and studies have shown feed costs to represent half or more of production costs and are, therefore, an important factor in determining the economic outcome for fish farms (Watanabe 2002;

Impacts of Nile tilapia cage culture on water and bottom sediment quality: The ability of an eutrophic lake to absorb and dilute perturbations

“…and TP (162.7 ± 5.6 μg/L) observed at the cage site at the end of the culture period could be attributable to nutrient leaching from fish feed and faecal matter, as well as metabolites. Previous research reported poor FCR (2.6) for fish feeds used in the study area (Musa, Aura, Tomasson, et al, 2021) which could have caused disproportionate increases in the TP and TN loadings. This suggests that fish cage culture in freshwater lakes such as Lake Victoria raises concerns about water quality deterioration attributable to both solid (Aura, Nyamweya, et al, 2018;Ngupula et al, 2012) and soluble wastes, especially nitrogen and phosphorus compounds.…”

“…In contrast to conventional land‐based aquaculture pond systems, cage systems do not use organic or inorganic fertilizers with high N and P contents, even though they are essential elements for organismal development. Accordingly, fish feed for cages have been reported to contain higher P contents than required by the fish (Ackefors & Enell, 1994; Musa, Aura, Tomasson, et al, 2021; Von Sperling & Chernicharo, 2005). Thus, the highest levels of TN (423.2 ± 1.4 μg/L) and TP (162.7 ± 5.6 μg/L) observed at the cage site at the end of the culture period could be attributable to nutrient leaching from fish feed and faecal matter, as well as metabolites.…”

“…Thus, the agro‐industrial and municipal sewerage TP and TN discharges through the major rivers is estimated to be 2,113,000 and 12,193,000 kg/year, respectively. On the contrary, it estimated that the Anyanga cage culture site, the epicentre of cage aquaculture in Lake Victoria, produces 20,480 kg of N and 970.7 kg of P per each fish production cycle (Musa, Aura, Tomasson, et al, 2021). Thus, the agro‐industrial and sewerage discharges contribute more than 2000 and almost 600 times the quantity of P and N into the lake, compared with fish cage culture contributions.…”

“…to contain higher P contents than required by the fish (Ackefors & Enell, 1994;Musa, Aura, Tomasson, et al, 2021;Von Sperling & Chernicharo, 2005). Thus, the highest levels of TN (423.2 ± 1.4 μg/L)…”