Growth, metabolic rates and body composition of individually reared triploid tilapia (oreochromis niloticus) in comparison to diploid full-sibs

Growth, Metabolic Rates and Body Composition of Individually Reared Triploid
Tilapia (Oreochromis niloticus) in Comparison to Diploid Full-Sibs
Ulfert Focken1, Gabriele Hörstgen-Schwark2, Christian Lückstädt1 and Klaus Becker1
1 Department of Animal Nutrition and Aquaculture in the Tropics and Subtropics, Hohenheim University 480b, Fruwirthstr. 12, 70599 Stuttgart, Germany, E-mail: 2 Institut für Tierzucht und Haustiergenetik, Universität Göttingen, Albrecht-Thaer-Weg 3, 37075 Göttingen, Germany, E-mail [email protected] Introduction
The culture of tilapia, mostly Nile tilapia, Oreochromis niloticus, has been expanding all overthe tropics for the past decades. In contrast to many other species, it is cultured in a widerange of environments from freshwater to marine and at all possible levels of intensity.
However, problems common for many tilapia culture systems are the reduction of growthrates at the onset of sexual maturity and undesired reproduction, leading to high numbers ofsmall fish (stunting). Brämick et al. (1995) confirmed triploidization as a tool to preventstunting effects in extensive pond culture of Nile tilapia, Oreochromis niloticus. In theirexperiments, no differences in growth between triploids and diploid controls could beobserved at age of maturation (6 weeks of grow-out), however, at the time of harvest (25weeks of grow-out), triploids were significantly heavier (p< 0.01) than control fish. This wascontrary to results gained from experiments under laboratory conditions (Don and Avtalion,1986; Penman et al., 1987, Puckhaber and Hörstgen-Schwark, 1991). It was speculated thattriploid tilapia may have gained the observed growth advantage only due to stunting effectsin control ponds, although predator controlled cultivation of diploid tilapia was used. Inaddition, breeding activities of fish seemed to be responsible for decreasing growth in diploidfemales at time of maturation. In order to evaluate the (physiological) effects of triploidy inNile tilapia we set up an experiment to compare growth, metabolic rates and bodycomposition of individually reared triploid Nile tilapia with diploid full-sibs.
Materials and Methods
Experimental fish
The same population of Oreochromis niloticus (originating from Lake Mansala, Egypt) as in
the earlier lab (Puckhaber and Hörstgen-Schwark, 1991) and field experiments (Brämick et
al, 1995) was used. The brood stock of this population was kept at the Institut für Tierzucht
und Haustiergenetik, Universität Göttingen, where the experimental groups were established.
In order to produce diploid and triploid full sibs, an egg batch was randomly taken from a
single pair mating and divided into two groups. While one group remained untreated (diploid
control), eggs of the other group were heat-shocked to induce retention of the second polar
body. Heat-shock treatment was applied at 41°C for a duration of 4.5 min, 4 min post
fertilization, as described by Puckhaber and Hörstgen-Schwark (1991). Triploidization
success was confirmed by chromosome preparations (Kligerman and Bloom, 1977, adapted
by Puckhaber and Hörstgen-Schwark, 1991) in a random sample of ten embryos out of the
treated group. At the age of 90 days 60 diploid and 60 triploid fish with an average weight of15 g were transfered to the aquaculture laboratory of the Department of Animal Nutrition andAquaculture in the Tropics and Subtropics, Hohenheim University, where they were groupreared untill the beginning of the experiment.
Experimental Setup
At the age of 128 days, diploid and triploid tilapia with an initial body mass of 27g (20 fish
each) were stocked individually in aquaria (20l) connected to recirculating systems.
Concurrently, 7 diploid and 8 triploid fish were stocked individually in the boxes (5l) of a
recirculating respirometric system (Focken et al., 1994) for the continuous individual
recording of oxygen consumption. All systems were equipped with biological filters for
nitrification. NH
3 and NO2 levels were below 0.2 and 2mg/l respectively at any time. In order to prevent high nitrate levels, 10% of water were exchanged every day. Watertemperature was kept at 27°C (± 0.1°), an artificial light regime was set at 12h light:12h dark.
Feeding Regime
The fish were fed a diet with 33.8% crude protein, 13.5% lipids and 7.1% ash, gross energy
was 21.7kJ/g (all dry matter base). This diet was mostly plant derived, with soybean meal as
main protein source. Feed allowance was based on the metabolic body mass (power 0.8) of
each individual fish and was adjusted weekly according to body mass changes. Feeding rate
at a given day was identical for all fish. During the first week of experiment, fish were fed at
maintenance level in order to determine their metabolic rates at this level. Feed allowance at
this time was 3.5g/kg0.8/d. During the second week, feed allowance was gradually increased
to 17.5g/kg0.8/d and kept at this level until week 8. To ensure complete ingestion of the feed
by all fish, from week 9 to week 17, feed allowance was reduced to 14g/kg0.8/d. The daily
ration was given in 6 equal installments during the light time by means of automatic feeders.
Fish were fed 6 days/week, there was no feeding on the day of the weekly sampling.
Sampling and Analytical Procedures
The fish were sampled every week in order to monitor their body mass development. For
this, the fish were taken out from their aquaria by a scope net and weighed to 0.1g in a pre-
tared bucket half filled with water. The metabolic growth rate has been calculated as body
mass gain per metabolic body mass per day (Dabrowski et al., 1986). Oxygen consumption
data were taken every 45 minutes for each box. From these raw data, hourly rates were
calculated, averaged over 1 week and standardized for the metabolic body mass.
The experiment was terminated after 17 weeks. For chromosome examination of each fish,colchicine solution (2%) was injected into the dorsal muscle (2 mg/kg). Four hours later, thefish were killed. Gill tissue was then taken and treated like the embryonic tissue describedabove The correct ploidy staus was confirmed for each individual. Body mass, length andheight of each fish were measured. After opening the abdominal cavity, sex and maturitystatus were recorded and the weight of the gonad taken. The carcass was autoclaved,homogenized, deep frozen, lyophilized and ground to a fine powder. This was analyzed fordry matter, protein, lipid and ash content according to the official German procedure asoutlined by Naumann and Basler (1983), i.e. macro-Kjeldahl-N times 6.25 for protein,Soxleth extraction with petrol-ether for lipids, combustion at 480°C for ash. Gross energy was determined by isoperibolic bomb calorimetry (IKA C 7000) using a benzoic acidstandard.
Statistics
All data were analyzed for significant effects (sex or ploidy or interaction between these) by
Two-Way ANOVA Option of GRAPHPAD Prism 3.0. Sigificance level was set at 5%.
Body mass development and metabolic growth rates
The body mass development of the experimental fish is given in Fig. 1. At the beginning of
the experiment, there were no significant differences in body mass between male and female
& -Diploid, n = 14
& -Triploid, n = 18
% -Diploid, n = 13
% -Triploid, n = 10
Time in Weeks
Figure 1: Body mass development of diploid and triploid tilapia Oreochromis niloticus.
S : effect of sex on body mass, * : significant at p < 5%, or diploid and triploid fish. Triploid males had the highest average body mass throughout theexperiment. For the first 5 weeks, diploid males rank second. After 2 and 3 weeks, males aresignificantly heavier than females. After week six, triploid females replace diploid males inthe second rank, but the difference between diploid and triploid fish is not significant at anytime throughout the experiment. The metabolic growth rates (Figure 2) were around6g/kg0.8/d in the second week (gradual increase in feeding rate), males performedsignificantly better than females, the same holds true for triploid fish compared to diploidfish. In the following week, at a constant feeding level of 17.5g/kg0.8/d, growth rates almostdouble and than decrease gradually towards the end of the experiment. From week 3 toweek 11, typically the metabolic growth rate of triploid females is highest, after that date, thetriploid males rank first. Except for the first week and week 14, where the poor performanceof females was highly significant, there are no statistically significant differences due to sex or ploidy status, significant interaction (different effect of triploidy on males and females)could be observed only once in week 15, but as there is no significant effect of sex or ploidystatus at that time, this result must be considered incidential. The metabolic growth ratescalculated for the entire experiment are given in Table 1, there are no significant effects ofeither sex, ploidy status or interaction.
& -Diploid, n = 14
& -Triploid, n = 18
% -Diploid, n = 13
% -Triploid, n = 10
Time in Weeks
Figure 2: Metabolic growth rate of diploid and triploid tilapia Oreochromis niloticus.
S : effect of sex on growth rate, P : effect of ploidy status on growth rate,I : interaction between sex and ploidy status, * : significant at p < 5%, ** : significant at p < 1% Feed conversion
Feed conversion (FC, Figure 3) follows a pattern similar to metabolic growth rate. In the first
week of intensive feeding, all groups have FC values above 1, however, these cannot be
sustained, from week 4 to week 13, FC is around 0.5, after that date, it drops further towards
the end of the experiment. Triploid females usually perform best up to week 10, after that
date triploid, later diploid males rank first. Again, significant effects can be observed only in
weeks 14 (highly significant sex effect and significant ploidy effect) and 15 (significant
interaction). Data for FC for the entire period are given in Table 1, there are no significant
effects.
& -Diploid, n = 14
& -Triploid, n = 18
% -Diploid, n = 13
% -Triploid, n = 10
Time in Weeks
Figure 3: Feed conversion of diploid and triploid tilapia Oreochromis niloticus.
S : effect of sex on growth rate, P : effect of ploidy status on growth rate,I : interaction between sex and ploidy status, * : significant at p<5%, ** : significant at p<1% & -Diploid, n = 4
& -Triploi d, n = 6
% -Diploid, n = 3
% -Triploi d, n = 2
Feeding close to satiati on
Maintenance
Time in Weeks
Figure 4: Oxygen consumption rates of diploid and triploid tilapia Oreochromis niloticus.
Oxygen consumption
Oxygen consumption data show a marked difference between the first week at a feeding rate
of 3.5g/kg0.8/d (maintenance level) and the remaining time when fish were fed close to
satiation (Figure 4). Diploid fish tend to have slightly higher oxygen consumption compared
to their triploid sibs, but this is not statistically significant at any time.
Morphometric data
Length, height and condition factor of the fish at the end of the experiment are given in
Table 1. While the effect of sex on length is not significant, triploid fish are significantly
longer than their diploid sibs. Condition factor of triploid fish is slightly lower (although not
quite significant), indicating a more elongate shape compared to the diploid fish.
Gonadal state and gonadosomatic index
All fish had reached sexual maturity (at least for females stage 3 according to the scale by
Kronert et al., 1989, >20 eggs visible, for males stage 4 according to scale by Oldorf et al.,
1989, testes white, thickened) at the end of the experiment. First mature diploid females were
observed in week 6 (average body mass of diploid females 45 - 50g). At the end of the
experiment, most triploid females were in the phase of resorption of eggs, while diploid ones
were in any stage between 3 and 6 (spent). Diploid and triploid males were mostly in stage 7
( ripe-running) at the end of the experiment.
The gonadosomatic index (Table 1) of diploid fish was almost double that of the triploid onesin both sexes, this effect is highly significant. For both diploid and triploid fish, GSI is about50% higher in females compared to males (significant), there are no indications forinteraction between sex and ploidy status.
Chemical composition of carcass and GE
Dry matter content in fresh matter as well as protein, ash, ether extract and gross energy of
dry matter are given in Table 1. Females have a higher content of dry matter in fresh matter,
this effect is very significant. Effects of ploidy and interaction on this parameter are not
sigificant. Protein and ash content of dry matter are relatively homogenous, there are no
significant effects for these. Sex has a very significant effect on the ether extract in dry
matter, ploidy has a significant effect. This results in the highest content in female triploids
(21.6%), followed by diploid females and triploid males (18.8% and 18.4%, resp.), diploid
males had lowest content (16.9%). For gross energy content, the ranking is the same as for
ether extract, however, only effect of sex is significant.
Discussion
For interpretation of the results of this study, the experimental conditions should be kept in
mind, especially that all fish were reared individually, and that feeding rate (relative to
metabolic body mass) was the same for all fish. This setup allows for the precise analysis of
the physiological potential of the experimental fish, as factors like differences in voluntary
feed intake and in competitional behavior are completely eliminated.
Body mass development, metabolic growth rate and feed conversion follow a patterntypically observed under our experimental conditions, i.e. an initial boost followed by arather stable phase at lower levels. Towards the end of the experiment, there may have been a growth limitation due to available space especially in the respirometric boxes. Growth ratesare similar to those achieved in another experiment using the same feed formula (Schreiber etal. 1998), but the feed seems not to be optimal as higher growth rates could be achieved byfishmeal based diets under identical experimental conditions (Santiago et al., 1998).
No obvious reason can be given for the dramatic increase in oxygen consumption and drop ingrowth rates and feed conversion and the respective standard deviations around week 13. Asall groups are affected by this more or less the same way, it is most likely an external effect,e.g. an influence from the tap water used in partial exchange of water in the recirculatingsystems, however, no change has been recorded in the external parameters monitored in thisexperiment.
Combining the results for metabolic growth rate, oxygen consumption and body compositionof diploid and triploid fish, it can be concluded that the triploid fish had slightly lower energyexpenditure (oxygen consumption), but this advantage cannot be channeled into overallgrowth but only into lipid accretion. Puckhaber (1992) reports that triploid females had twiceas much lipid accretion in the abdominal cavity as diploid ones, while there were nodifferences between diploid and triploid males. Lipid content in muscles was higher intriploid fish of both sexes.
The relatively homogeneous growth of diploid and triploid tilapia is in contrast to thefindings of an earlier lab study by Puckhaber and Hörstgen-Schwark (1991) in which triploidfish had a significantly lower weight at 136, 178 and 220 days compared to a diploid control.
In contrast to the study presented here, fish were reared in groups. There is quite goodagreement between the growth observed in our experiment and in the pond experiments byBrämick et al. (1995) until the onset of sexual maturity. The fact that in our experiment thegrowth of diploid and triploid fish was comparable after the onset of sexual maturity supportsthe hypothesis of Brämick (1995) and Brämick et al. (1995) that the significant difference inbody mass between diploid and triploid fish in pond culture was due to reproduction andincreasing competition of the diploid fish.
References
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