EFFECTS OF DIFFERENT DURATION OF FEEDING ON RESULTS OF CARP (CYPRINUS CARPIO) FRY CAGE CULTURE IN COOLING WATER

Jacek Sadowski, Jarosław Filipiak, Rajmund Trzebiatowski

ABSTRACT

The “Safir” trout feed (Aller Aqua) was offered to carp (Cyprinus carpio) fry of 21 + 5 g/ind. initial weight, stocked at a density of 300 ind./m³ in cages placed in cooling water. Identical rations (5 – 4.0% metabolic weight) were offered for 6, 12, and 18 h per day. The data obtained showed the best results (as indicated by SGR and FCR) of culturing carp of up to about 75 g individual weight were obtained when the feeding took 18 h, 12 – 18 h being the best duration of feeding for the carp weighing 75 – 130 g. No effect of duration of feeding was observed in the carp weighing more than 130 g.

Key words: carp, cooling water, feeding time, metabolic daily ration..

INTRODUCTION

Water temperature [1, 10] and oxygen content [15] are regarded as the most important environmental factors affecting fish growth. Neither in open nor in cooling waters can those factors be adjusted by man. For this reason, when culturing fish, attempts are made to optimise fish growth rate by, i.a., using appropriate diets [7, 10, 12] and adjusting feed rations [7, 8, 13]. Relatively few studies were carried out on frequency and duration of feeding [2, 5, 9] as factors determining fish growth rate. For this reason, an attempt was made in this work to study effects of feeding time on results of carp fry culture in cooling water.

MATERIALS AND METHODS

The study was carried out within 1 August – 6 September 1995 at the Agricultural University of Szczecin Department of Aquaculture’s Fisheries Research Station (FRS), situated in the vicinity of the “Dolna Odra” power station at Nowe Czarnowo. Carp fry (0+) of about 20 ą5 g mean individual weight, purchased from a pond fish farm, was stocked in 1 m³ working capacity net cages; the stocking density was 300 ind./m³.

The fish were fed daily for 6, 12, and 18 h with the 2 – 5 mm pellet diameter “Safir” extruded trout feed (Aller Aqua) containing 47.2% protein, 17.5% fat, and 5308 kcal gross energy content. Daily feed rations, calculated with respect to the fish metabolic weight (W^0.8), were identical in each experimental treatment and ranged, depending on water temperature and fish weight, within 5.0 – 4.0% (Table 1).

The magnitude of daily food ration, dispensed each day from 9:00 hours on by timer-fitted feeders, was calculated from the formula:

   (1)

where:

DFR, daily food ration (kg),
MFR, metabolic food ration (%),
n, number of fish in a cage,
W, mean individual fish weight (kg).

To follow the dynamics of changes in the major culture parameters, and to adjust the food rations, the fish from all the cages were weighed, to 0.05 kg, every 6 – 8 days. The data obtained served to calculate mean values of Food Conversion Ratio (FCR), Specific Growth Rate (SGR), apparent Net Protein Utilization (aNPU), Energy Retained (ER), and apparent Lipids Retained (aLR) as in the formulae below:

   (2)

where:

T, number of days elapsed,
W_ip, initial mean individual fish weight (g),
W_ik, final mean individual fish weight (g);

   (3)

where:

P, amount of food offered (kg),
W_k, final weight of fish in a cage (kg),
W_p, initial weight of fish in a cage (kg);

   (4)

where:

B, crude protein weight in fish body on termination of the experiment (g),
B₀, crude protein weight in fish body before the experiment (g),
N_p, crude protein weight in the food offered (g);

   (5)

where:

E_k, gross energy content in fish body on termination of the experiment (kcal),
E_p, gross energy content in fish body before the experiment (kcal),
EP, gross energy content in the food offered during the experiment (kcal);

   (6)

where:

T, weight of lipids contained in fish body on termination of the experiment (kg),
T₀, weight of lipids contained in fish body on day 1 of the experiment (kg),
T_p, weight of lipids contained in the food dispensed during the experiment (kg).

To check for significance of differences between the experimental treatments, the LSD test at P = 0.05 was applied to all the parameters calculated.

At the beginning and on termination of the experiment, 5 individuals were picked from each experiment treatment to determine, after homogenisation, per cent contents of dry matter (drying for 12 h at 105°C), crude protein (Kjeldahl technique, Kjeltec 1026 apparatus), lipids (Soxhlet technique; 12 h ethyl ether extraction), and ash (combustion for 12 h at 550°C). Similar assays were performed on the feed, the carbohydrate content being calculated in both cases as a difference between the dry matter and the sum of the remaining components. To calculate the gross energy content, the values given by Brody [4] as 5.65 kcal/g crude protein; 9.45 kcal/g lipids; and 4.1 kcal/g carbohydrates were used.

Water temperature, oxygen content, and pH were determined quasi-continuously (every 60 min) with an automatic recorder. The mean, maximum, and minimum daily values of the environmental parameters are shown in Figs 1A-C.

RESULTS AND DISCUSSION

Frequency with which the feed is administered is one of major elements of fish feeding regime. In the present study, timer-equipped feeders dispensed the feed continuously, in small portions, for different periods of time.

Effects of feeding time on results of culture are related to the fish gut capacity and duration of food passage through the gut, the passage time decreasing with increasing water temperature [18]. In the case of rainbow trout, the frequency of feeding higher than twice a day did not result in an increase in the amount of food consumed [3]. According to Ruohonen [16], the rainbow trout growth rate increases with frequency of feeding, the highest growth rate occurring at 60 feed portions a day. Similar experiments demonstrated an optimal feeding frequency to be two portions per day for Ictalurus punctatus [2], one portion per day for Channa striatus [17] and Salvelinus alpinus [11], and one portion every other day for Epinephelus tauvina [6].

In their studies on feeding carp individuals weighing 173 mg, Charles et al. [5] found the highest growth rate to accompany 3 food portions dispensed per day. On the other hand, Omar and Gunther [14] showed that a higher SGR was attained in feeding carp 6 portions a day than at 4 daily portions. The experiments referred to above did not involve feeding frequencies higher than 6 feedings a day, i.e., the frequencies much lower than those applied in our study. It was in the experiment described by Hogendoorn [9] only that the frequency of feeding the African catfish (Clarias gariepinus) of 0.5 g/ind. was similar to that in this work. We demonstrate that, when the timer-equipped feeders dispense the feed over 24 h, a higher growth rate is attained than when the feeders work for 12 h (during the day or at night) or when the food is offered two or four times a day. At the same time, no statistically significant differences between feed conversion ratios obtained with 4 portions a day and with 24 h feeding could be demonstrated. The highest growth rate of individuals weighing about 75 g each was arrived when the food was offered for 18 h (Table 1). The best results with respect to the fish weighing from 75 to about 120 – 130 g each were recorded at 12 and 18 h feeding times (no significant differences in SGR and FCR between the two treatments) (Table 1). Once the fish grew to more than 130 g/ind., neither their growth rate nor feed conversion ratios showed statistically significant between-treatments differences. On termination of the experiment (6 September), the fish were still kept in the cages and fed identical feed rations. The initial differences in growth rates resulted in mean individual weights as recorded on 4 October, i.e., 63 days after stocking, being 385, 492, and 516 g for the fish fed for 6, 12, and 18 h a day, respectively. Thus the differences emerging during the experiment resulted in the final weight of fish fed for 18 h a day to be b y as much as 34% higher than that of the fish fed for 6 h daily.

Among the data reported in Table 2, noteworthy is the aLR value, the lowest in those fish fed for 18 h a day and resulting in the lowest body lipid content (Table 3). This result is most likely related to the duration of feeding. The fish obtaining their entire daily food ration (and thus the entire daily energy supply) during 6 h adjusted their metabolism accordingly: they digested more feed and accumulated more energy per unit time than those fish obtaining an identical food supply during a longer period of time, which most probably resulted in a higher accumulation of energy (in the form of body lipids) in the first. Moreover, those fish feeding for 12 and 18 h were forced to prolong their feeding activity, which may have resulted in their lower lipid retention.

To sum up, duration of feeding is one of the most important elements of carp fry culture in cages placed in cooling water. An appropriate adjustment of feeding time allows to considerably improve the results of culture. Prolonged duration of feeding seems to improve effects of culturing fish of a low individual weight as the carp have been observed to be capable of feeding throughout the day. Thus it seems purposeful to carry on studies on effects of feeding duration in order to further improve carp culture and feeding regimes.

CONCLUSIONS

1. Effects of duration of feeding on growth rate and feed conversion ratios in carp depend on the fish individual weight.
2. The best culture results are obtained when carp weighing 75, 75-130 g/ind., and more are fed for 18, 12, and 6 h a day, respectively.
3. Extension of feeding time results in reduced aLR and body lipid content of carp.

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