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The literature contains a large number of data (Pavlov et al, 1970; Kasumyan, Kazhlaev, 1993, Mamedov et al., 2009; Shamushaki et al., 2007) on the development of the olfactory and taste sensitivity to food chemical signals and behavioral search reactions in ontogeny of sturgeon species. However, information regarding food behavioral response of ship of Kura population (Acipenser nudiventris Lovetzky) and its hybrids with other species of sturgeon to various chemical stimuli and food objects are very limited. Insufficient information regarding the behavior of the ship sturgeon and other aspects of its biology. Apparently is explained due to the poor accessibility of the ship for experimental studies because of the small density of this fish in the natural waters, and

their rare appearance in last year's at the farm conditions. Ship of Kura population included in the "Red Book" of Azerbaijan and is fished only for reproductive purposes. Given the above, the scope of this work was to study the development in ship ontogeny the of a behavioral food search response evoked by chemical stimuli, as well as to determine the sensitivity of ship to these stimuli.

Materials and methods.

The study was carried out in 2006-2007 at the Khylly Sturgeon Fish Farm of Azerbaijan. Objects of study were the larvae and juveniles (aged 8-45 days, 5 months and 10 months after hatching) of ship of belonging to the Kura River population. Fish were grown up in pools. Body length, weight and age (from hatching) of experimental fishes are shown in

Table 1.

The number of experiments which were performed on the each of fish age groups were ranged from 6 to 8. The water temperature during Behavioral trials were carried out in experimental two-section aquariums with water flow. The concept of experimental aquarium as well as the methodology of the behavioral experiments and evaluation of the intensity of fish behavioral response was described in details in early publications above (Kasumyan, Kazhlaev, 1989, 1993, Kasimov, Mamedov, 1990, Mamedov et al., 2009). The solutions of monosodium glutamate - MSG

(NaOOCCH2CH2CH (NH2)-COOH) were used as the chemical stimuli.

Concentration of solutions MSG was expressed in mol / l.

Results and discussion.

Observing the behavior of the pre-larvae of ship in the pools showed that the period of their rest is less than at pre-larvae of Russian sturgeon. Kura ship pre-larvae begin to show motion activity for 3 days prior to the beginning of active (exogenous) feeding. At the age of 10-12 days (the first 1-2 days of active feeding), most of the ship larvae moves along the bottom of the aquarium, some larvae occasionally quickly rise into the upper layers of the water, and then, after a short swim, sink to the bottom

again. Injection into the aquarium MSG solutions in concentration from 10-3 to 1 mol /l does not cause any changes at the background behavior of the larvae of this age (Table 1).

Table 1. The intensity of the food search reactions (in 5-points scale) evoked by solutions of MSG in different concentrations in ship having different age

Object of researches

MSG concentration, mol /l

Length L, mm

Weight P, mg

Age, days.

1

101

102

103

104

 

20

37

10

0

0

0

0

0

-

27

100

14

1,240,1

1,1±0,1

0,6±0,1

0,3±0,1

0

-

37

310

25

2,9±0,1

1,8±0,1

1,4±0,1

0,9±0,1

0,4±0,1

0

51

820

35

3,240,1

2,3±0,1

1,5±0,1

1,2±0,1

0,9±0,1

0

69

1830

45

3,2±0,1

2,3±0,1

1,6±0,1

1,4±0,2

0,9±0,1

0

120

6750

180

3,2±0,1

2,6±0,1

1,6±0,1

1,6±0,2

0,9±0,1

0

210

28700

300

3,2±0,1

2,9±0,1

1,6±0,1

1,6±0,2

0,9±0,1

0

After the transition to the full exogenous feeding (age of 14 days) the ship larvae still actively swam most of the time at the bottom of the aquarium. Acts of catching of organic particles lying on the bottom of the aquarium by touching with their barbels has been observed rarely. Introduction to the aquarium of the sodium glutamate solution in concentration 1 mol / l evokes a obvious behavioral response ship larvae of this age: 10-20 seconds after beginning of SGM injection larvae that are near the entrance of the compartment with odour, sink to the bottom and began to show the characteristic elements of search behavior -moving along a zigzag trajectories. During the movement along these trajectories fish touched the bottom surface of aquarium with the ends of the barbels. Frequency of catching acts and moving activity in individuals responding to chemical stimulus had increased significantly. The total duration of the reaction was no more than 5-6 minutes.

The intensity of behavioral response of ship at the age of 25-27 days to the solution of sodium glutamate becomes significantly stronger. The characteristic elements of search behavior - moving along the bottom of the aquarium in circular and S-shaped loop paths and zigzag trajectories, and a high frequency of acts catching as well. Such characteristic

elements demonstrate often the fish that are close to the compartment with the odour , as well as in the surrounding areas of the aquarium bottom. Reacting specimens demonstrate the high motion activity. The most intensive search behavior show the individuals being in the compartment with the stimulus. In this area the gathering of fish is formed that vigorously and repeatedly moved in circular and S-shaped path, making frequent acts of catching. While moving at the search circular and S-shaped path fish makes yaws - small displacement of the head and the front part of the body on either side of the main direction of motion. Ship show low response to solutions of sodium glutamate concentration 10-4 mol / l.

The background behavior and the search response is not significantly altered in fish on the next age group (35-40 days). A distinctive feature of the behavioral response of the fish of this age is more pronounced ability to locate the source of a chemical signal, a longer time for complete decay of the reaction (5-6 minutes), and the display of search behavior, not only in the area of maximum concentration, but also on a wider section of the bottom of aquarium. Behavioral response was observed up to a concentration of a solution of sodium glutamate 10-4 mol/l.

Behavioral experiments performed on the juveniles at age of 5 and 10 months shown that the definitive level of chemical sensitivity of ship at this age is the same as in much younger fish at the age of 35-40 days -

10-4 mol / l.

At the result of the present study it was found that the chemical sensitivity to food chemical signals in the ontogeny of the Kura ship occurs immediately after the transition of young fish to full exogenous feeding. Similar results were obtained in other species of sturgeon (Kasimov, Mamedov, 1990; Kasumyan, Kazhlaev, 1989, 1993). In particular, it was found that the ability to respond to extracts of food organisms occur in the ontogeny of Russian sturgeon (Acipenser gueldenstaedtii), Siberian sturgeon (Acipenser baerii) and stellate sturgeon (Acipenser stellatus) after the transition to full exogenous nutrition in 8-12 days after hatching.

Peculiarities of the ship reaction and first of all orientation of fish to

odour source indicates the ability of young ship relying on the perception of food chemical stimuli, not only to obtain information about the presence of food signal in the water, but also to search for its source.

The researches conducted in other species of sturgeon has shown that young sturgeon reaches definitive level of olfactory sensitivity to food odors by the second month of their life, about 20 days after appearance of ability to respond to these signals. It was found that the development of olfactory sensitivity to food chemical odors in the Russian sturgeon (Acipenser gueldenstaedtii), Siberian sturgeon (Acipenser baerii) and stellate sturgeon (Acipenser stellatus) ended when the young fish reaches an age of 35, 38 and 35 days after hatching, with a body length of 45; 42 and 38 mm and a weight of 650, 520 and 242 mg, respectively (Kasumyan, Kazhlaev, 1993 Kasimov, 2003, etc.). This process is completed simultaneously with the formation of the definitive level of olfactory sensitivity to food chemical signals. This is also demonstrated by a study of the cytoarchitectonics of olfactory bulb of sturgeons, which shows that by the age of 35 days the allocation of core cell layers in it completes (Rustamov, Obukhov, 1986). It was found that the level of definitive olfactory sensitivity in the aforementioned types of fish to extract of food organisms is 0.0001 g / l. This level of sensitivity is typical for fish with low level of development of vision ablity, such as, in particular, the sturgeons. In ship the definitive level of chemical sensitivity to a solution of sodium glutamate in the age of 35-40 days makes 10-4 mol /l, and further increase of the sensitivity (aged 5-10 months) does not happen.

The studies found that the behavioral response to a food chemical signal in the young fishes of various species of sturgeon occurs on a single stereotype. Absence of any significant species specific differences in reaction of ship from other sturgeon species, apparently occurs due to the substantial similarity overall strategies of sturgeon (Pavlov, Sbikin, 1989), the proximity of functional development and the role of food search response of distant sensory systems of distant action.

Data on the time of formation of the search reactions can be used to adjust the size-age standard artificially reared sturgeon juveniles released into natural water bodies. The findings suggest a promising job on creation

of high olfactory stimulant of feeding behavior for sturgeon, which can be widely used to improve the attractiveness of the scent of artificial feed.

References

Kasimov R.Yu. Physiological and ecological justification of terms of release of sturgeon young fishes from farms in Azerbaijan // Proceedings of the International Conference "Modern problems of biological resources of the Caspian Sea." - Baku. - 2003. - P. 23-26. (in russian).

Kasimov R.Yu., Mamedov Ch.A. Behavioral responses and possibilities of learning yuveniles of the South-Caspian Sturgeon population to various substances dissolved in water and the role of chemosensory systems in their provision // Izv. Akad. Nauk Az. SSR. Ser. Biol. - 1990. - N. 1. - P. 94-102. (in russian).

Kasumyan A.O., Kazhlaev A.A. Behavioral response of sturgeon fish to the natural

chemical signals food // "Chemosensitivity and chemocommunication of fish." -Moscow. - 1989. - P. 167-174. (in russian).

Kasumyan A.O., Kazhlaev A.A Formation of search behavioral response and olfactory sensitivity to food chemical signals in ontogenesis of Acipenserids // Vopr. Ikhtiology. - 1993. - Vol. 33. - N. 2. - P. 310-320.

Mamedov Ch.A., Gadzhiev R.V., Akhundov M.M. New technologies of sturgeon cultivation in Azerdaijan. Baku: Elm, 2009. - 260 p. (in russian).

Pavlov D.S., Sbikin Yu.N., Popova I.K. Role of senses during feeding of yuveniles of Acipenserids // Zool. Zh. - 1970. - Vol. 49. - N. 6. - P. 872-880. (in russian).

Pavlov D.S., Sbikin Yu.N. Some results of the study of the behavior of sturgeon // "The morphology, ecology and behavior of sturgeon." - Moscow: Nauka, 1989. - P. 124-141. (in russian)

Rustamov E.K., Obukhov D.K. The development of the olfactory bulb in the ontogeny of sturgeons // Journal of Evolutionary Biochemistry and Physiology. - 1986. - T. 22. - N. 3. - P. 294-298. (in russian).

Shamushaki Jafari V.A., Kasumyan A.O., Abedian A., Abtahi B. Behavioral response of Persian sturgeon, Acipenser persicus juveniles to free amino acid solutions // Mar. Freshwater Behavioral Physiology. - 2007. - V. 40. - N. 3. - P. 219-224.

Effect of Weaning Age on Growth And Survival of Pikeperch (Sander Lucioperca) Larvae

Hadis Mansouri Taee1, Hossein Ouraji2, Hossein Rahmani2, Iraj Efatpanah Komaie3, Mahmood azimirad4

1 Young Researchers Club, Khorramabad Branch, Islamic Azad University, Khorramabad, Iran;

2 Department of Fisheries, Sari Agricultural Sciences and Natural Resources University, Iran;

3 Dr.Yousefpour Marine Fish Propagation, Rearing and Restoching Center (Siahkal-Guilan-Iran);

4 Department of Fisheries, Faculty of Natural Resources, University of Tehran, Karadj, Iran

Abstract

The aim of current study was to find the optimal transition time from live food to artifical food in pikeperch (Sander lucioperca) larvae. In this experiment, pikeperch larvae were fed with seived pond zooplankton and Artemia nauplii from the first feeding up to day 16 post-hatching (16 dph), then three weaning times were used on 16 , (W16), 22 (W22), 28 (W28) dph and compared with a control group (fed on live food only). According to the obtained results, the best growth (mean weigth gain = 152.78+2.97 mg) and the highest survival rate (61.85+2.51%) were reported in control group. The lowest weight gain (mean weigth gain = 28+5.58 mg) and the lowest survival rate (13.33+5.30%) were observed in larvae weaned at 16 dph. As the larvae fed live food had the best growth performance it is assumed that the most suitable method for pikeperch larvae rearing was exclusively with live food, however, the results of growth performance in larvae weaned at 28 dph was noticeable.

Keywords: Sander lucioperca, Larvae, Weaning, Artifical food, Live food

Pikeperch, Sander lucioperca (previously named Stizostedion lucioperca) is a valuable species for aquaculture due to its rapid growth, flesh quality and high commercial value Hamza et al. (2008). This species, had been introduced into water reservoirs in several European countries Larsen and Berg (2008). Pikeperch is found in freshwater and brackish water in the Caspian watershed (Ural, Volga, Kura and Sefid Roud rivers) and in the basins of the Black, Azov, Aral, and Baltic Sea Craig (2000) and it is one of the most valuable fish in the southern part of Caspian Sea and distributed from the Gorgan Bay to the Anzali Lagoon Abdoli and Naderi (2009). Pikeperch stocks in the Caspian Sea declined during the past decades because of over-fishing and destruction of natural spawning sites Ivanov (2000). To restock this valuable species in the Caspian Sea, the Iranian fisheries organization annually produces and releases pikeperch fry into the Caspian Sea. Total fry production of pikeperch increased from 3.9 million in 2000 to more than 16 million in 2006. (Iranian fisheries organization annual report, 2008).

In Iran, the larval rearing of pikeperch takes place in the earthen ponds and stocking of ponds with pikeperch larvae is done when rotifers bloom. In ponds, pikeperch larvae initially feed on rotifes and when the larvae size increases, feed on copepod nauplii azimirad (2010). However, production of pikeperch fry using artificial food is not practised yet.

The weaning time of pikeperch larvae has been investigated in several studies, but different results were obtained (Xu et al., 2003; Ostaszewska et al. 2005; Hamza et al.,2007; Kestemont et al., 2007). In one study Kestemont et al. (2007) on weaning time, the highest final body weight of pikeperch larvae was found in larvae weaned at 19 dph , while the survival rates of larvae was generally poor. But a recent study Hamza et al. (2007) reported that pikeperch larvae can be weaned from 15 dph without significant negative effects on digestive enzymes or development of digestive tract. However, in their study, the final body weight of larvae in 36 dph that weaned from 15 dph was very low.

According to Canavate and Fernandez-Diaz (1999), growth and

survival are powerful tools understanding the effects of both live food and artificial diet on first-feeding of fish larvae. Therefore, this study was carried out to specify the most appropriate weaning time for pikeperch larvae and evaluate the effects of various weaning times on larvae.

Materials and Methods

Facilities and Fish

In this experiment, the larvae used (16 dph) were the offspring of one batch of eggs from semi artificial spawning with hormonal injection Kucharczyk et al. (2007) wild females and males caught in the spawning season (lately winter season) in Aras dam, Urmia, Iran. The brood stocks were transported to the Center of Renewing Fish Resource Yosefpoor, Siahkal, Iran. After spawning on nest, incubation, hatching and yolk sac resorption, 6-day old larvae were fed add-libitum a mixture of sieved zooplankton (mainly rotifers) collected from ponds and Artemia nauplii at 4 h interval throughout the day from 8 am to 8 pm, then two thousand four hundred 16 dph were distributed in to the 12 circular tanks (200 larvae per each tank). The flow rate in each tank was approximately 0.5-1 L min-1 with a slight aeration. Tanks were cleaned by siphoning once a day to remove the unconsumed food, fish waste and dead larvae Kestemont et al. (2007).

The larvae were kept in outdoor flow-through water tanks supplied by filtered pond water (filter size = 50 u). Temperature and dissolved O2, controlled daily, was kept at 19°C and above 6 mg L-1, respectively. pH was determined twice a week and observed at level 7-8 Szkudlarek and

Zakes (2007).

Experimental Diets

In this experiment, four different treatments (three weaning times and a control group) were applied in triplicates (4 x 3 =12 tanks). Three weaning times were applied on 16 (W16), 22 (w22) and 28 (W28) dph. The larval feeding scheme is summarized in Table 1. A mixture of sieved zooplankton (mainly rotifers) and newly-hatched Artemia fransiscana

nauplii were used as first live foods from 6 to 16 dph and then newly-hatched Artemia nauplii was used alone as live food from 16 dph up to the end of experiment. The commercial diet Bio Optimal (0.5 mm) was used as the weaning feed to replace the live food. The weaning procedure consisted of decreasing the proportion of Artemia nauplii while increasing the proportion of dry feed (Artemia nauplii:dry feed in a ratio of 75:25, 50:50, 25:75 and 0:100%) within 4 consecutive days Kestemont et al. (2007).Control groups were fed with Artemia nauplii from first feeding to the end of the experiment (34 dph). All groups of larvae were fed at 4 hour interval throughout the day from 4 am to 12 pm manually. Larvae were fed 100% biomass during experiment and approximately 200-600 Artemia nauplii fish-1 day-1 was targeted for the control group

Kestemont et al. (2007).

Table 1: Feeding regimes followed during the larval rearing of Sander lucioperca

Days (dph)

Control

W16

W22

W28

6-16

Artemia+Rotifera

Artemia+Rotifera

Artemia+Rotifera

Artemia+Rotifera

16-22

Artemia

BioOptimal

Artemia

Artemia

22-28

Artemia

Bioptimal

Bioptimal

Artemia

28-34

Artemia

Bioptimal

Bioptimal

Bioptimal

Sampling procedures

Every 6 day, 10 pikeperch larvae from each replication (30 larvae per treatment) were sampled and weighed collectively by precision balance (0.1 mg sensitivity) while the total length individually was measured. The number of dead larvae was recorded daily. The number of sampled larvae was taken into account for survival. Growth parameters and survival rate were calculated as follows: formulas:

• Gain of Body Mass ,GBM=final body weight (mg)-initial body weight (mg);

• Avarage Daily Growth, ADG(mgxdays-1)=(final body weight (mg)-initial body weight (mg))x rearing period-1 (days);

• Specific growth rate, SGR (% day-1)=100x(ln final body weight (mg)-ln initial body weight (mg))xrearing period-1 (days);

• Condition factor, CF = 100x(body weight (mg)xbody length SL-3

(mm));

• Survival Rate, SR (%)=100x(final abundance (individuals)xinitial abundance-1 (individuals));

• Mortality Rat, MR (%)=100x(initial abundance (individuals)-final abundance (individuals))x initial abundance-1 (individuals)

Statistical Analysis

All statistical analysis were performed using statistical package SPSS, version 16.0. Data that expressed as percentages were subjected to arcsine transformation before statistical analysis. The homogeneity of variances of means was tested by Levene's test. When data were normally distributed, the mean values for each parameter of different treatments were analyzed by one-way analysis of variance (ANOVA). When significant differences among treatments were found (P<0.05), the means were compared with Duncan's multiple range test.

Results

The growth performance data and survival reate of sander lucioperca larvae in different trearments are presented in Table 2. Based on results, the highest weight gain and specific growth rate were observed in larvae fed only live food during the whole period of rearing (control group). On the other hands, the lowest weight gain and specific growth rate were found in larvae weaned at 16 dph. According to the results (Table 2), larvae weaned on day 28 (W28) showed significantly (P < 0.05) higher weight gain and specific growth rate compaire to the larvae weaned on 16 (W16) and 22 (W22) dph. By extending the period of feeding with live food, weight gain, specific growth rate and avarage daily growth rate of pikeperch were increased. The highest survival rate was obtained in larvae fed only live food during the whole period of rearing (Fig. 1). The mean survival rates of larvae weaned on day 22 and 28 post-hatching

were 19.26±6.09 and 48.89±0.96%, respectively. The highest mortality rate was recorded in larvae weaned at 16 dph (Table 2).

Table 2: Growth parameters and survival of Sander lucioperca larvae in experiment treatments

Treatments

Parameters

Control

Weaning 28

Weaning 22

Weaning 16

Final weight

155.30±2.97d

115.15±2.80c

56.95±1.61b

30.52±5.58a

GBM

152.78±2.97d

112.63±2.80c

54.43±1.61b

28.00±5.58a

ADG

5.46±0.11d

4.02±0.10c

1.94±0.06b

1.00±0.20a

SGR

14.72±0.07d

13.65±0.09c

11.13±0.10b

8.87±0.67a

CF

1.06±0.09c

1.10±0.06c

0.75±0.03b

0.62±0.03a

CMR

38.15±2.50a

51.11±0.96b

80.74±6.10c

86.67±5.30c

Groups with different alphabetic superscripts differ significantly at P<0.05

Conra] WIS W22 Wit)

Treatment

Fig 1. Mean survival rate of Sander lucioperca larvae in relation to different weaning time. Values are mean ± SD of triplicates (10 larvae sampled per replicate, n=30). Control: fed only on live food; W16: larvae weaned at day 16 post-hatching; W22: larvae weaned at day 22 post-hatching; W28: larvae weaned at day 28 post-hatching.

Discussion

The determination of the optimum weaning time of pikeperch larvae is one of the key factors to the further development of pikeperch

intensive larviculture Kestemont et al. (2007). Results of the present study showed that live foods were more efficiently utilized by the pikeperch larvae and larvae fed only on live food during the whole period of experiment showed the best growth performance. The higher efficiency of live foods for larvae was attributed to the presence of digestive enzymes in live foods that help in the digestion processes (Verreth et al., 1993; Kolkovski et al., 1995).

On the other hand, the lowest growth and survival were observed in larvae weaned at 16 dph . The poor response of 16- day old larvae to artificial feed could be related to the incomplete development of the digestive system and poor effeciency in digestion and assimilation. A study by Hamza et al. (2007) suggested that pikeperch larvae can be weaned from 15 dph without significant negative effect on digestive system (except for alkaline phosphatase). However, it should be mentioned that in that study, growth performance of larvae weaned at this age (15 dph) was poor and survival rate was not reported. On the other hand, Kestemont et al. (2007) reported that the optimal weaning age for pikeperch larvae was on 19 dph while the survival rate of larvae at this weaning age was 15.3%. They also observed the highest survival rate (24.8%) in larvae fed on only Artemia nauplii. Survival rate and growth performance of larvae are powerful tools to evaluate the success of weaning time. If weaning time larvae is not suitable, it leads to a poor performance in terms of survival and growth in larvae.

The present study showed that larvae weaned on 28 dph obtained significantly higher weight gain and specific growth rate than larvae weaned on 16 and 22 dph. This results indicate that at this age the acceptance of artificial feed by pikeperch larvae have been improved and probably digestive capability of pikeperch larvae developed. This finding is supported by Hamza et al. (2007) who stated that pikeperch larvae acquire the adult mode of digestion around 29 dph. They reported the appearance of gastric glands with pepsin secretion and pyloric caeca at

29 dph.

Generally, the acceptance of artificial diet by larvae depends on a number of factors, i.e. suitable size, texture of feed and aroma of feed

Dabrowskii (1984). In this study, a commercial diet (Bio optimal) with suitable size and good nutritional quality was used at the weaning time and larvae were fed add-libitum to ensure availability of food to each larva. Howevere, observation of feeding behaviour of larvae showed that after adding dry feed to the experimental tanks in weaning times of 16 and 22 dph , just some of the larvae attracted to the dry diet and consumed it. Therefore, the high rate of mortality obsrved in W16 and W22 treatments could be explained by the poor utilization of artificial feed after weaning. Kestemont et al. (2007) stated that the high mortality of pikeperch larvae between the ages of 12 and 18 dph was related to the non-feednig phenomen in which larvae were attracted towards the tank walls and refused feeding.

In conclusion, from the biological point of veiw, the most suitable method of pikeperch larvae rearing was only with live food during the whole period experiment (until 34 dph). However, the results of growth performance in larvae weaned at 28 dpg age was noticeable. In other words, mean weight gain of larave in W28 treatment was three-forth (75%) of larvae fed only on live food. Therefore, it is possibel to rear the pikeperch larvae using artificail feed from 28 dph.

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Influence of replacing fish oil with canola oil on nutritive value of Rainbow Trout

Ali Masiha1, Eisa Ebrahimi1, Nasrollah Mahboobi Soofiani1, Mahdi Kadivar2, Mohammad Reza Karimi1

1Division of Fisheries, Department of Natural Resources, 2Department of Food science, College of Agriculture, Isfahan University of Technology. masiha.ali@gmail.com

Introduction

In the course of just a few decades, fish farming has developed into a highly productive and efficient industry to produce animal protein for human consumption. In addition to good growing conditions, a prerequisite for productivity and economic sustainability in fish farming can be a reliable supply of effective feeds. For various reasons, fish meal and fish oil have historically been the dominant raw materials in the production of fish feeds. Due to the development of more energy dense feed types as well as general growth of the aquaculture industry, a significant proportion of the total global fish oil is used for its feed preparation. A lipid requirement equal to 100% of the world's total fish oil production is estimated by the year 2010 [24].

While marine oils are superior in their fatty acids composition they also contain a variety of toxic compounds including polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF) and dioxin-like polychlorinated biphenyls (DL-PCB), particularly the non-ortho and mono-ortho substituted PCBs [14, 15, 17, 18]. These compounds are suspected to be carcinogenic and immunosuppressive in humans [2, 6, 32]. It is also well-known that lipid oxidation is one of the major concerns in fish-derived food products. Polyunsaturated fatty acids (PUFAs) are more easily oxidized than saturated fatty acids (SFAs), and therefore, food products enhanced with the PUFAs n-3 are also more prone to lipid oxidation. There is potential human health risks associated with increased consumption of oxidized PUFAs n-3 products [10, 21].

While it is obvious that a substitute must be found, replacing fish oil in diets has its own difficulties as most of the vegetable oils are relatively poor sources of n-3 fatty acids. Exceptions to this are flaxseed and canola oils which are rich in alpha linolenic acid (18:3n-3) (53% and 12%

respectively) [25]. However, these oils are devoid of longer chain n-3 highly unsaturated fatty acids (HUFAs n-3) and their inclusion in trout diets results in a significant decrease in the tissue levels of eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-

3, DHA) [3, 4].

Freshwater fish are capable of converting C18 PUFAs to the longer chain C20 and C22 PUFAs [13] which are the functionally essential fatty acids in vertebrates [22].

The aim of the present study was to evaluate the effects of fish oil replacement with canola oil on nutritive value of fish for human consumption.

Materials and methods

Rainbow trout fingerlings with a mean initial body weight of 16.5+0.5 g were purchased from Cheshmeh Dimeh fish hatchery (Shahre kord, Chaharmahal and Bakhtiari, Iran) and used in this study.

Three iso-nitrogenous, iso-calorific and iso-lipidic purified experimental diets were formulated from 100% fish oil (FO), 100% canola oil (CO) and 1:1 blends of the oils (FCO). Diets were prepared and stored according to Abery et al., (2002) [1] and De Silva et al.,

(2002) [9].

This study was conducted indoors in a thermostatically controlled room. Fish were housed in nine 100 L fiberglass circular rearing tanks in a semi re-circulating system with an in-line oxygen generator and a physical and biological treatment plant (flow rate of 6 L min-1). During experiment, fish were kept under a 12-h light: 12-h dark cycle. The experiment was conducted at 13.6+1.3°C, water quality parameters were measured every second day using Aquamerck test kits (Merck, Darmstadt, Germany) with a mean pH of 7.3+0.2 and levels of ammonia and nitrate below 0.1 mg L-1.

270 individually weighed and measured fingerlings were randomly distributed into the tanks (30 fish per tank) and randomly assigned to one of the 3 different experimental diets (3 replicates for each experimental diets). Fish were fed twice daily at approximately 08.30 and 17.00 h to apparent satiation for a period of 56 days. At the end of the experiment a sample of 18 fish (2 fish per replicate) was taken and anesthetized in

excess anesthetic (Benzocaine 0.5 mg L-1) for fillet fatty acid profile analysis.

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