The effects of rearing density on growth, size heterogeneity and inter-individual variation of feed intake in monosex male Nile tilapia Oreochromis niloticus L.

Abstract

The growth dispersion of farmed fish is a subject of increasing interest and one of the most important factors in stocking density. On a duration of 60 days, the effect of stocking density on the growth, coefficient of variation and inter-individual variation of feed intake (CVFI) of juvenile Nile tilapia Oreochromis niloticus L. (14.9 ± 1.2 g) were studied in an experimental tank-based flow-through system. Groups of fish were stocked at four stocking densities: 200, 400, 600 and 800 fish/m3, corresponding to a density of ∼3, 6, 9 and 12 kg/m3 and referred to as D1, D2, D3 and D4, respectively. Each treatment was applied to triplicate groups in a completely randomized design. No treatment-related mortality was observed. The fish densities increased throughout the experiment from 3 to 23.5, 6 to 43.6, 9 to 56.6 and 12 to 69 kg/m3. Results show that mass gain and specific growth rate (SGR, %M/day) were negatively correlated with increased stocking density. Groups of the D1 treatment reached a mean final body mass (FBM) of 119.3 g v. 88.9 g for the D4 groups. Feed conversion ratios (FCRs) were 1.38, 1.54, 1.62 and 1.91 at D1, D2, D3 and D4 treatments, respectively. Growth heterogeneity, expressed by the inter-individual variations of fish mass (CVM), was significantly affected by time (P < 0.001), stocking density (P < 0.001) and their interaction (P < 0.05). The difference in CVM was particularly conspicuous towards the end of the experiment and was positively correlated with stocking density. Similarly, radiographic study shows that CVFI was also found to be significantly greater for groups reared at high stocking densities (D3 and D4) than the other treatments (D1 and D2). These differences in both CVM and CVFI related to the stocking density need to be taken into account by husbandry practices to assure the production of more homogeneous fish size. A simple economic analysis indicates a parabolic relationship between profit and density with optimal final density at the peak of the curve. Given reasonable assumptions about production costs, the optimal final density (D opt) is 73.7 kg/m3. A sensitivity analysis shows that changes in the fixed cost have no effects on the optimal final density. However, small change in variable costs, such as feed and juvenile costs, may have substantial effect on the optimal density.

Bioeconomic modeling of optimal harvest time in Nile tilapia (Oreochromis niloticus) considering size heterogeneity and minimum marketable size

“…Regarding the selection process, the results coincide with the reports by Azaza et al (2013), and Khaw et al (2016), in which the organisms with less dispersion contributes to obtaining more significant economic benefits. A common practice in aquaculture is to repeatedly select organisms during culture to reduce size variation during growth.…”

Effects of stocking density on growth of zebrafish (Danio rerio, Hamilton, 1822)

“…This parameter (SGR) decreased with increasing density which was 1.71 ± 0.02 to 0.56 ± 0.02. Azaza et al (2013) also reported that SGR is affected significantly by stocking density and they observed highest SGR for lowest stocking density for Nile tilapia (Oreochromis niloticus). FCR increased with increasing stocking density and the range of FCR was 1.85 ± 0.02 to 2.56 ± 0.11 (Fig.…”

“…On the other hand, relatively high rearing density hampers fish health and welfare as well as their production due to stress, predation and competition for food, so the determination of optimal rearing density is a precondition for maximum growth for highest production that leads to maximum profit. Therefore, the impact of rearing density on growth and reproduction of some fish species has been recorded like Atlantic salmon Salmo salar (Hosfeld et al 2009), rainbow trout Oncorhynchus mykiss (McKenzie et al 2012), Nile tilapia Oreochromis niloticus (Azaza et al 2013) and Japanese Medaka Oryzias latipes (Rosemore and Welsh 2012). An interesting work was carried out by Castranova et al (2011) who worked on zebrafish and suggested that using densities as high as 12 fish/liter does not have a negative effect on reproductive performance.…”

Effect of size heterogeneity of Nile tilapia (Oreochromis niloticus) on the optimal harvest time: a bioeconomics approach

“…A critical problem in the production of Nile tilapia Oreochromis niloticus in intensive and hyper-intensive systems (30-400 fish m -3 ) is the heterogeneity of body size. The organisms in the same cohort show different growth rates in response to biotic and abiotic factors (Barbosa et al, 2006;Azaza et al, 2013).…”