FCR values of tilapia fry in our study varied between 1.45 and 1.66,
which is in agreement with the results of El-Tawil and Amer (2010), who
reported FCR values of 1.45–1.66 when feeding Nile tilapia with 5%–15%
Ulva sp. meal. Anh et al. (2013) observed FCR values 0.93 to 2.47 in red O.
niloticus on a diet of 0% to 33% Enteromorpha-enriched feed.
Our PER ranged between 2.01 and 2.29, in agreement with Anh et al.
(2013), who noted a similar range of PER (1.83–2.28) in case of the red O.
niloticus on diets with 0% to 33% Enteromorpha-enriched feed.
Replacing fish meal protein with plant protein in fish feed generally
affects the whole-body composition of fish (Shelton 2002). In the present
study, the lipid content of monosex male tilapia fry significantly decreased
with increasing GW level in the diets, similar to the observations of Appler
and Jauncey (1983). Conversely, protein content was highest in fish maintained
at 10% GW and 20% GW in the diets. Protein content was higher in
the common carp at 15% Ulva sp. and the gray mullet at 28% Ulva sp. han
in control fishmeal diets (Diler et al. 2007).
Increasing GW protein from 10% to 50% in the diets reduced feed prices
by 4.43% to 15.74% compared to the 0% GW protein diet. Overall, the best
diet in terms of cost per kg of fish flesh was observed in fish fed the 20%
fishmeal replaced diet.