Rasanthi M. Gunasekera

Interactions of varying dietary protein and lipid levels in young red tilapia: Evidence of protein sparing

A 12-week feeding trial was carried out with young red tilapia, a hybrid of Oreochromis mossambicus and O. niloticus, with a mean weight of 1.185 g. Three series of isocaloric, experimental diets of 15%, 20% and 30% protein content (by dry weight) and for each series, four diets of 6%, 12%, 18% and 24% lipid content were tested. At all three protein levels the best growth was obtained with diets of 18% lipid. Daily consumption (in mg/g fish day−1) was correlated negatively to the digestible energy content of the diets, and overall rate of growth positively to the mean daily protein consumption (per g fish per day). The food conversion ratio ranged from 1.10 (P30L24) to 2.32 (P15L12), the protein efficiency ratio from 2.18 (P30L6) to 3.56 (P20L18) and apparent net protein utilization from 19.9% (P15L6) to 42.95% (P30L18), where P and L refer to dietary protein and lipid, and the subscripts to the approximate percentage. The carcass lipid and protein reflected the dietary regimes. The study indicates the protein-sparing capabilities of young red tilapia. The protein-sparing capability increased with increasing dietary lipid content up to 18% and decreased thereafter.

Effect of dietary protein level on puberty, oocyte growth and egg chemical composition in the tilapia, Oreochromis niloticus (L.)

Abstract Oreochromis niloticus were maintained on 5 isocaloric diets of different dietary protein levels (10, 17, 25, 32 and 40%). In Expt. 1, O. niloticus (initial mean weight approximately 0.3 g) maintained on diets of 10 and 17% protein levels showed lower growth rates compared to those on the higher protein levels and none reached puberty. In Expt. 2 (initial mean weight approximately 3 g), only those receiving 10% dietary protein level gave similar results; fish fed 17% reached puberty. Fish fed higher protein levels (32 and 40%) reached puberty at an earlier age, with oocytes growing and maturing faster, than those fed lower levels (≤ 25%). The former also showed higher growth rates, lower food conversion ratios and higher survival rates. When the onset of puberty and the rate of oocyte maturation were evaluated in relation to size (regardless of age), there were no significant differences among the treatments, suggesting that dietary protein may have influenced oocyte growth and puberty by its effect on growth. The chemical composition of post-vitellogenic oocytes, expressed as percent protein, lipid, moisture, and essential amino acids (mg in 100 mg protein), was not significantly different among the different dietary treatments.

Effect of dietary protein level on spawning performance and amino acid composition of eggs of Nile tilapia, Oreochromis niloticus

Abstract Oreochromis niloticus were maintained on three purified, isocalorific diets of different dietary protein levels (10, 20 and 35%), with casein and gelatin as protein sources. The dietary protein influence on spawning interval, fecundity, relative fecundity (number of eggs per unit weight) and egg size at four successive spawnings was investigated. The protein, moisture, free and bound amino acid composition of the spawned eggs were determined. O. niloticus females fed 20 and 35% protein levels maintained their spawning cycle, whereas at 10% spawning intervals were prolonged after about 4 months of feeding. Females fed 20 and 35% protein diets produced a higher number of eggs per spawn than those fed 10%, especially at later spawnings. But relative fecundity and egg size did not differ significantly between the treatments. The amount of protein in eggs of females maintained on 35% protein diet was significantly higher than in others. However, the moisture content of the eggs did not vary among the diets. Of the free amino acids, methionine, valine, tyrosine, serine, glycine and proline were influenced by the dietary regime. The total (free + protein bound) individual amino acids in the eggs were not affected by dietary protein level. However, the total overall amino acid pool of eggs in the 35% protein level was higher than in the others.

Influence of protein content of broodstock diets on larval quality and performance in Nile tilapia, Oreochromis niloticus (L.)

Abstract Performance of mature Nile tilapia females reared on three isocaloric, purified, diets of 10, 20 and 35% crude protein (CP), for a minimum period of 4 months, in relation to fertilizability, hatchability and larval quality was investigated. Care was taken to minimize the influence of males on egg and larval quality, and to ensure that the results reflect the nutritional history of the brooding females. The eggs of females reared on the 10% CP diet were not fertilized. The means of the number of eggs per spawn, egg diameter and percent fertilizability were 359 ± 31 and 398 ± 39, 2.29 ± 0.05 and 2.31 ± 0.05 mm, and 79.8 ± 4.2 and 83.8 ± 3.9 for females fed on 20 and 35% CP diets, respectively. The differences between the diets for the above parameters were not significant. However, the percent hatchability (20% CP 41.7 ± 5.1; 35% CP 68.7 ± 3.6) of the eggs and the percentage of normal larvae (20% CP 41.8 ± 4.4; 35% CP 59.8 ± 2.8) from the females on 35% CP diet were higher ( P Significant differences were, however, observed in the free amino acid content of larvae from the two groups of females, but not in other chemical traits such as total protein or moisture content. A relationship was evident between fertilizability and hatchability of eggs to their free amino acid content.

Changes in the fatty acid profiles of hybrid red tilapia, Oreochromis mossambicus X O. niloticus, subjected to short-term starvation, and a comparison with changes in seawater raised fish

Juvenile hybrid red tilapia of mean weight 52.9 ± 2.80 g were starved for 45 days, and the liver and muscle fatty acid profiles of fed and starved fish determined on Days 0, 24 and 45. A corresponding group of fish were seawater adapted and were sampled on Day 45. In fed fish the total fatty acids in the livers (expressed in μg mg−1 lipid) decreased with growth (45 days), from 816 ± 16 to 600 ± 7 and 821 ± 25 to 589 ± 23 in females and males, respectively. This decrease was significant by the 24th day. In muscle, however, the amount of fatty acids in total lipid increased with growth, in females from 365 ± 21 to 489 ± 6 and in males from 387 ± 17 to 480 ± 17 μg mg−1 lipid. Compared with fed fish, during starvation the proportion of fatty acids in total lipid increased in both types of tissues but was still lower than at the initial level, significantly so in the liver. Twenty individual fatty acids were quantified as percent of total fatty acids in liver and muscle tissues of fish from different treatments during this study. In starved fish, liver monoenes decreased significantly (P < 0.05), from 33.0 to 16.3% and 35.6 to 9.5%, and the percentage of polyunsaturated fatty acids (PUFA) increased significantly from 18.3 to 39.9% and 16.9 to 46.2% in females and males, respectively. Comparable trends were also observed in muscle, but in muscle the percentage of PUFA tended to be higher than in the liver. The fatty acids that occurred in the highest proportion were oleic acid (18:1 n − 9), followed by palmitic acid (16:0) and docosahexaenoic acid (DHA; 22:6n − 3), collectively accounting for more than 50% of the total. The relative amount of PUFA, in particular DHA, increased considerably and very significantly with starvation. Principal component analysis of the fatty acid data effectively summarized the major differences among the experimental treatments, which included substantial differences in the fatty acid profiles between sexes, fed and starved animals and between fish raised in fresh- and seawater.

Influence of dietary protein content on the distribution of amino acids in oocytes, serum and muscle of Nile tilapia, Oreochromis niloticus (L.)

In this paper changes in the physical and chemical characteristics including the amino acid content of mature oocytes (Stage 4; pear-shaped; > 2.4 mm diameter) of Oreochromis niloticus females in relation to dietary protein content of 10, 20 and 35% are presented. Corresponding changes in amino acid content of dorsal muscle and serum (18 h post-prandial) were also investigated in the females sampled. The amount of protein in oocytes of females maintained on the 10% protein diet was significantly lower (P < 0.05) than the others. However, the gonadosomatic index of females and the diameter, mean weight and moisture content of oocytes were not affected significantly by the dietary protein levels. Diet related changes were observed in total (protein-bound + free) amino acid patterns in oocytes and muscle. Total essential amino acid patterns of muscle and oocytes were positively and significantly correlated to those of the diets, but with respect to the total non-essential amino acids, only the dietary amino acid patterns for the 20 and 35% protein diets were correlated to that of muscle. Serum and oocyte free essential and non-essential amino acid patterns were also highly correlated with dietary amino acids at all three dietary levels. The significance of these observations is discussed in light of possible ‘maternal compensation’, whereby the female attempts to channel essential nutrients to developing oocytes even when her nutrition is sub-optimal.

An evaluation of the growth of Indian and Chinese major carps in relation to the dietary protein content

Published data on growth in Indian and Chinese major carps in relation to the dietary protein content, where the total energy content of the diets was 16–20 kJ g−1 and at least 10% of the protein source was from fish meal, were utilized in this study. The relationship of rate of growth (% increase in body weight per day, % ADG) to dietary protein content (% Pr) is best described by a second-order curve common to all species presently investigated, by the equation, log % ADG=−0.029+0.042 (%Pr)+(−0.0005 (%Pr)2) (d.f.=39; r=0.62; P<0.01). The dietary protein content at which maximal growth occurred was 45% and the economically optimal dietary protein content was 31%. The significance of these findings from an aquaculture point of view is discussed and the findings are compared with those from a similar study with tilapiine fish.

Lipid and fatty acid digestibility of three oil types in the Australian shortfin eel, Anguilla australis

The lipid and fatty acid digestibilities of three semi-purified, isonitrogenous (48.9–50.8% protein) and isocalorific (19.1–20.8 kJ g−1) diets, in which the lipid source was either cod liver oil (CLO), linseed oil (LO) or sunflower oil (SFO), were estimated in the Australian shortfin eel (Anguilla australis) using chromic oxide as an external marker. Apparent percent protein and energy digestibilities of the diets were not significantly (P>0.05) affected by the lipid source, but the lipid digestibility was. The percent apparent lipid digestibility was lowest in the LO diet (90.2±0.6) and highest in the CLO diet (95.6±0.2). Not all the fatty acids present in any one diet were recovered in the faecal samples. In diets with CLO, only three saturates (out of five), five monoenes and six (out of 11) PUFAs were detected in faecal samples. With all the diets, 20:0 and 22:0, and none of the n−6 HUFA were detected in the faecal samples. The digestibility of all the fatty acids, except 18:3n−3, was lowest in the diet with LO, and significantly so (P>0.05) from the other diets. In shortfin eel, there was a trend for the digestibility of saturated fatty acids of diets with the animal oil as the lipid source to decrease with increasing chain length, and in diets with vegetable oil to increase initially and then decrease. A somewhat comparable trend was also evident in respect of monoenes. When the digestibility of different categories of fatty acids is considered, the digestibility of saturates, monoenes, unsaturates, n−6, PUFA, HUFA and total fatty acid digestibilities of LO diet were the lowest, and differed significantly (P<0.05) from those of the CLO and SFO diets, except in the case of n−3 fatty acids.

Influence of dietary protein level on ovarian recrudescence in Nile tilapia, Oreochromis niloticus (L.)

Abstract Ovarian recrudescence was investigated in Nile tilapia, reared on isocaloric, semi-purified diets of 10, 20 and 35% protein content, for 2 and 4 month periods. Females immediately after spawning were used with a view to ensuring that all individuals investigated would have ova in a regressed state initially, so that subsequent changes could be correlated to dietary protein affects. In females reared for 2 months, the dietary effects on ovarian recrudescence became most evident only by Day 14, when a significantly higher percentage of Stage 4 oocytes (diameter > 2.4 mm, pear-shaped, bright yellow, post vitellogenic oocytes) were present in the 35% protein fed females as compared to those fed the 10% protein diet. In females reared on the diets for 4 months, comparable differences were evident on Day 7 after spawning. Here ovarian recrudescence of 10% protein fed females was slower than in females maintained on 20 and 35% dietary protein levels. In females reared for 2 and 4 months on the experimental diets, GSI, however, did not vary significantly amongst fish fed 10, 20 and 35% diets, in the regressed and recrudescing ovaries at Day 7 and Day 14. There was evidence to indicate that even when the females are reared on a sub-optimal diet (e.g. 10% protein) they make an attempt to go through the recrudescence process, perhaps by utilizing existing body reserves.

Changes in the amino acid profiles during embryonic development of the blacklip abalone (Haliotis Rubra)

Changes in the total amino acid (TAA) and the free amino acid (FAA) contents during embryonic development, through newly spawned eggs, to pre-settled larvae of blacklip abalone (Haliotis rubra) are described. The TAA (protein bound + free) and the FAA contents increased prior to hatching but decreased towards settlement, but the changes were not always significant between different stages of development. Threonine, arginine, lysine and leucine accounted for nearly 50 % of the total essential amino acids (TEAA) in all developmental stages. The mean FAA content of newly spawned eggs was 262.8± 28.2 pmol·ind -1 and accounted for 11.5 ± 8.3 % of the TAA. Free essential amino acid (FEAA) content increased significantly as development progressed (P < 0.05), in which threonine, arginine and lysine accounted for over 63 % of this pool. In all developmental stages, the FAA pool was dominated by the non-essential amino acids taurine + proline which accounted for 79.5 % of the total. Generally, the FAA accounted for between 10 to 15 % of the TAA in the different developmental stages of blacklip abalone. All evidence appears to indicate that in blacklip abalone the energy requirements during early ontogeny are mostly met with from the lipid reserves, and that there is a tendency to conserve amino acids until pre-settlement.