Growth And Survival Of Huso Huso Larvae Biology Essay

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Co-feeding of fish larvae with live food and formulated diet has been at the focus of fish nutritionists since last decade. In this study we tried to refine the feeding practices of great beluga sturgeon (Huso huso) larvae using different combinations of newly hatched Artemia urmiana nauplii and trout starter diet. Three replicate groups (250 fish/replicate) of first-feeding Huso huso larvae were fed on the basis of four main feeding regimens: (1) live food (live nauplii of brine shrimp Artemia urmiana); (2) indirect transition (5 days live food followed by gradual transition to formulated diet); (3) direct transition (using different combinations of live and formulated diet from start feeding); (4) formulated feed (FD). It was found that combining live food and manufactured diets (co-feeding) from first feeding stage (direct transition) significantly improves the weight gain in H. huso larvae followed by indirect transition, live food and FD. But survival was significantly higher in larvae fed on pure live food and direct transition regimens compared to indirect transition and FD. It was concluded that co-feeding of H. huso could be started immediately from commencement of exogenous feeding.

Introduction

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Economically, sturgeons are very important in Caspian Sea fisheries. Five different species of sturgeons, namely Acipenser persicus, Acipenser stellatus, Acipenser nudiventris, Acipenser guldenstadti and Huso huso live in the Caspian Sea. Huso huso is the largest fish in the Caspian Sea producing the most costly roe. Therefore this fish has been the focus of much attention in Iran since last decade because it is particularly interesting species in terms of rearing value. However, there is very little information on the feeding patterns of this fish. This is especially true of the larval and juvenile stages, which are the most critical stages in the life-cycle of the fish.

At the onset of exogenous feeding, different sturgeon species present an anatomically complete digestive tract with a marked specialization of each of its different segments (Buddington & Christofferson, 1985; Gawlicka et al., 1995; Gisbert et al., 1998). As a consequence, artificial larval diets have been used for intensive commercial culture of several acipenserid species from the onset of exogenous feeding (Charlon & Bergot, 1991; Giovannini et al., 1991; Hung, 1991; Gisbert & Williot, 1997). However, the end of the lecithotrophic stage and transition to exogenous feeding still represents an important source of larval mortality (Buddington & Christofferson, 1985; Giovannini et al., 1991; Gisbert & Williot, 1997; Bardi et al., 1998), suggesting some nutritional problems associated with the digestion and assimilation of artificial diets, which are normally formulated for salmonids or marine fish species (Hung, 1991; Gisbert & Williot, 1997). Combined feeding of live and manufactured diets, referred to as co-feeding, from the start of exogenous feeding or from an early larval age, could be considered as an alternative strategy.

Mohler et al (2000) indicated high survival in Atlantic sturgeon Acipenser oxyrinchus oxyrinchus using Artemia nauplii and commercial feed. They reported a complete conversion to formulated feed with less than 25% mortality in 20-26 day feeding trial. Dilauro et al (1998) offered five different formulated diets in combination with live brine shrimp Artemia sp., to the Lake sturgeon Acipenser fulvescens larvae. They reported no diet effect (P ≤ 0.05) on mean survival between the groups, but significantly higher growth in fish fed on only brine shrimp. Ware et al (2006) investigated the effects of six feeding regimens on the survival and growth of cultured shortnose sturgeon fry in 30 days feeding regimes using formulated diet and cofeeding the live and formulated feeds. They reported significantly higher survival and growth in groups co-fed with Artemia compared to live food and commercial feed alone. Bardi et al (1998) reported higher than 95% survival in Mexico sturgeon Acipenser oxyrinchus desotoi larvae when fed on brine shrimp compared to nearly complete mortality (>99%) when fed on formulated feed during a 3 weeks feeding trials. According to their findings diet-switching experiments revealed that survival and growth rate of first-feeding larvae increased if they were fed brine shrimp for 1 week and then switched to experimental microdiet.

A number of other studies have demonstrated the effectiveness of co-feeding in enhancing the marine and freshwater larval performance beyond that achieved by feeding either types of feeds alone (Kanazawa et al., 1989; Holt, 1993; Leu et al., 1991; Abi-Ayad and Kestemont, 1994; Vega-Orellana et al., 2006; Curnow et al., 2006b; Hamza et al., 2007; Rosenlund and Halldórsson, 2007).

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The aim of the present work was to investigate how different feeding regimes, live feed alone or co-fed with an inert diet, influence the survival and growth factors in H. huso larvae under controlled laboratory conditions.

Materials and Method:

Eight thousand 3-days old post-hatch yolk-sac larvae of H. huso were obtained from Shahid Marjani Sturgeon Hatchery and transported in oxygenated plastic bags to the Artemia and Aquatic Animals Research Institute, Urmia University. They were then stocked in a big tank containing UV-treated underground freshwater.

Tanks were supplied with UV treated fresh water obtained from a well with a flow rate of approximately 1L/min. Dissolved oxygen was maintained above 7 mg/L using constant aeration and fish were exposed to a natural photoperiod of approximately 12:12 L:D. Tanks were flushed daily in the morning to remove trapped feces. Water temperature was 20 ± 1°C and pH 7.30-7.50. Temperature, pH and dissolved oxygen were monitored once or twice daily. No other water quality parameters were measured due to the constant nature of the well water quality and high exchange rate of the water used in the tanks.

After absorption of their yolk sac, larvae were transferred to 45 liters polyethylene tanks. Two feeding groups were adopted. In the first group the fish larvae were fed on newly hatched Artemia urmiana nauplii (N) for 5 days followed by gradual replacement with commercially formulated trout starter diet (FD). Whereas in the second group the fish larvae were fed on different combinations of newly hatched Artemia nauplii and FD from the first day of exogenous feeding. Fish were fed on the basis of 35% body weight (first 5 days), 25% (days 6-10), 15% (days 11-15) and 10% body weight (days 16-20) respectively. Daily rations were divided into six equal meals and fed at the intervals of four hours. The experiment in both groups was continued for 20 days until all feeding treatments were totally converted to FD in all feeding treatments. Survival was monitored every day and zootechnical performances (total length, wet weight, dry weight, SGR and FCR) were accessed on days 7, 14 and 21 of the experiment according to standard methods.

Experimental feeding regimes:

Artemia nauplii (N) throughout the experiment

N for first 5 days + 10% daily replacement of N with FD from day 6 (total conversion to FD occurring on day 15)

N for first 5 days + 30% replacement of N with FD on day 6 and 10% daily additional replacement with FD from day 7 (total conversion to FD occurring on day 13)

N for first 5 days + 50% replacement of N with FD on day 6 and 10% daily additional replacement with FD from day 7 (total conversion to FD occurring on day 11)

N (90% feed weight) and FD (10% feed weight) on day 1 + 10% daily replacement of N with FD from day 2 (total conversion to FD occurring on day 10)

N (70% feed weight) and formulated feed (30% feed weight) on day 1 + 10% daily replacement of N with FD from day 2 (total conversion to FD occurring on day 8)

N (50% feed weight) and formulated feed (50% feed weight) on day 1 + 10% daily replacement of N with FD from day 2 (total conversion to FD occurring on day 6)

FD throughout the experiment

The approximate chemical composition of the formulated food and Artemia nauplii used in this study is shown in table 1.

Table 1: The chemical composition of Artemia nauplii and formulated diet. (The values indicate the averages values of replicates with standard deviations).

Feed

Crude protein (% DW)

Crude lipid (% DW)

Carbohydrate % DW

Ash (%)

Energy (cal.g⁻¹)

Formulated diet

50 ± 2

12 ± 1.5

12.5 ± 1

13.5 ± 1

4000 ± 31

Nauplii

61.6 ± 0.8

11.6 ± 2.1

20±2.9

6.8 ± 2

5013.1 ± 88.3

Statistical analysis was carried out using analysis of variance (ANOVA, SPSS ver 13). Differences between means were determined and compared by the Tukey test. All tests used a significance level of P ≤ 0.05.

Results:

Results obtained from the feeding experiments are briefly summarized in Tables 2 and 3. Growth of fish was significantly higher in all co-fed groups compared to the fish fed on only Artemia nauplii and FD (P < 0.05). Fish larvae receiving 70% Artemia nauplii and 30% commercial food on first day followed by 10% daily replacement with FD (treatment 6) demonstrated maximum growth. Lowest SGR and highest FCR were obtained in fish larvae fed on FD and Artemia nauplii respectively (P < 0.05). Although SGR was highest in treatment 6, but no statistical differences were observed among different cofeeding groups. We found that feeding H. huso larvae with combination of live food and FD from the beginning of exogenous feeding (direct transition) results in significantly higher weight gain compared to indirect mode of transition to FD. Very little growth and high mortality (mostly due to cannibalism) was observed in fish fed on FD compared to all feeding treatments. Significantly greater survival was observed in the fish fed on live food (70.6%) and in co-fed groups 5 and 6, (65.7% and 59.7% respectively) compared to fish in other feeding treatments. There was no significant difference in the survival of fish fed on live food and those co-fed with 10 and 30% FD from the beginning of exogenous feeding. It was observed that early co-feeding results in higher survival and weight gain compared to feeding on Artemia nauplii for 5 days and gradual shifting to FD. FCR was lower in all transition treatments compared to fish fed on live food and FD.

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Table 2. Initial and final length, wet weight and dry weight of H. huso larvae fed on different combinations of live food and commercial feed. (Initial total length, wet weight and dry weight were 25 mm, 59 mg and 10.3 mg respectively).

Treatments

Final length (mm)

Final W. Wt. (mg)

Final D. Wt. (mg)

1

57.6 ± 2.8a

1033.9 ± 236.4b

101 ± 43.8b

2

65.9 ± 2a

1566 ± 192.8c

188.1 ± 33.6c

3

65.5 ± 2.5b

1568.2 ± 109.1c

194 ± 6.1c

4

68.3 ± 2.9b

1645.6 ± 201.5c

205.2 ± 25.1c

5

68.9 ± 1.6b

1702.3 ± 100.4c

210.6 ± 11.7c

6

69.4 ± 2.2b

1814.5 ± 66.9c

233.4 ± 13.1c

7

66.2 ± 1.4b

1579.3 ± 115.8c

192.3 ± 13.4c

8

32.3 ± 2.2a

145.1 ± 15.7a

16.3 ± 3.2a

Different superscripts in each column indicate significant difference between treatments (p < 0.05).

Table 3. Mean SGR, FCR and survival of Huso huso larvae fed on different combinations of live food and commercial feed

Treatments

SGR

FCR

Survival

1

14.23 ± 1.17b

1.64 ± 0.4b

70.6 ± 3.4d

2

16.37 ± 0.6c

1.50 ± 0.07a

53.7 ± 2.3bc

3

16.39 ± 0.3c

1.47 ± 0.01a

50.8 ± 2bc

4

16.62 ± 0.6c

1.49 ± 0.02a

47.7 ± 3b

5

16.8 ± 0.3c

1.53 ± 0.03ab

65.7 ± 6.8cd

6

17.13 ± 0.2c

1.56 ± 0.01ab

59.7 ± 11bcd

7

16.43 ± 0.36c

1.50 ± 0.04a

52.7 ± 8.8bc

8

4.5 ± 0.5a

2.66 ± 0.1c

20 ± 2a

Different superscripts in each column indicate significant difference between treatments (p < 0.05).

Discussion

In most marine species compound diets fed alone have a poor ability to sustain fish larvae growth and development (Cañavate and Fernández-Díaz, 1999; Robin and Vincent, 2003; Curnow et al., 2006a). The low performance usually observed when feeding an inert diet from mouth opening to marine fish larvae may be due to sub-optimal diet composition and the larval poor ability to modulate its digestive enzymes (Cahu and Zambonino Infante, 2001). Therefore, feeding regimes based on a co-feeding strategy have been proposed for farmed species, such as dourado (Vega-Orellana et al., 2006), Asian sea bass (Curnow et al., 2006b), pikeperch (Hamza et al., 2007), and cod (Rosenlund and Halldórsson, 2007).

Artemia nauplii are used extensively world-wide as live food for the larval stages of commercially important fresh water and marine fish species. The cost in infrastructure, labour and energy to culture this zooplankton represents a significant expenditure and the supply and nutritional quality of brine shrimp can vary as well (Sorgeloos, 1980; Watanabe et al., 1983). Furthermore it seems that acceptable growth rates in a number of fish species cannot be maintained using live feed exclusively due to the low nutrient content and restricted feed intake (Olsen et al., 1992). This has prompted a great deal of interest in the development of an artificial larval microdiet (MD) as an economic alternative to live feeds. However, a lower performance is commonly reported when inert diets have been fed to larvae from the onset of exogenous feeding. They may be due to the composition, palatability, or physical characteristics of dry feed (Person Le Ruyet et al., 1993), or an inability to properly digest the feed (Holt, 1993; Kolkovski et al., 1993; Walford and Lam, 1993; Zambonino Infante and Cahu, 1994). But markedly improved performance were reported when inert MDs were co-fed with live zooplankton (Kanazawa et al., 1982; Szlaminska and Przybyl, 1986; Ehrlich et al., 1989; Fermin and Bolivar, 1991; Marte and Duray, 1991; Tandler and Kolkovski, 1991; Walford et al., 1991; Person Le Ruyet et al., 1993; Lavens et al., 1995).

Use of Artemia nauplii alone or co-fed with commercial diet at start feeding or during early development of different species of sturgeon fish has been reported by a number researchers (Dilauro et al. 1998; Bardi et al. 1998; Mohler et al., 2000; Volkman et al. 2004).

Results obtained in present study indicated that a carefully programmed use of live food co-fed with commercial diet could be successfully used in feeding great sturgeon (Huso huso) larvae from first feeding stage. The results indicated that co-feeding H. huso with live food and FD from the start feeding presented best performance supporting the findings of Ware et al. (2006) with shortnose sturgeon. Based on their findings, Acipenser brevirostrum exhibited higher survival and growth in different types of co-feeding regimens compared to live food regimen. H. huso larvae demonstrated significantly higher growth and survival when live food was combined with FD at start feeding compared to transition after 5 days initial feeding with live food. Unlike findings of Dilauro et al. (1998) and Bardi et al. (1998), our findings proved that H. huso can readily accept the co-feeding of live food and FD from first feeding without prior feeding on live food alone. H. huso larvae demonstrated high capacity for rapid transition to complete FD within 7 days from onset of exogenous feeding.

It has been proved that co-feeding enhances larval performance beyond that achieved by feeding either types of feeds alone (Kanazawa et al., 1989; Holt, 1993; Leu et al., 1991; Abi-Ayad and Kestemont, 1994), and to permit weaning in a shorter time (Person Le Ruyet et al., 1993). This finding seems to be true for both H. huso. An increased supply of more suitable nutrients may be the main effect of co-feeding on better performance of the fish larvae that accepts FD along with live food. However, the fish larvae suffered significantly high mortality when they were offered only formulated diet from first feeding. It seems that a large number of larvae die from starvation, showing little interest on formulated diet as sole diet. Feeding on FD alone resulted in high cannibalism in H. huso larvae, proving that inert food alone does not meet all their nutritional requirements at first feeding. Apparently there is a specific period during development when different sturgeon fish larvae will eat manufactured diets and this seems to be related to their behavioural and physiological capacity. It seems that successful co-feeding depends on the ability of the fish larvae to eat dry feed when live feed is also present.

It is concluded that H. huso larvae could be co-fed with a combination of Artemia nauplii and commercial feed from onset of exogenous feeding with rapid total conversion to FD within 7 days. Co-feeding resulted in considerable reduction of consumable costs (including Artemia cyst), materials, personnel and space needed for preparation of feed and feeding process. Co-feeding in H. huso seems to serve two purposes; it improves and stabilizes the nutritional condition of the larvae and it pre-conditions the larvae to accept the manufactured diet when the live food is withdrawn, resulting in a shorter weaning period.

Acknowledgements

This study was carried out with the financial support of the Artemia and Aquatic Animals Research Institute, Urmia University, Iran.