Growth response and aggressive behaviour of Clarias gariepinus fingerlings reared at different photoperiods in a water re-circulatory system

S G Solomon and V T Okomoda

Department of Fisheries and Aquaculture, University of Agriculture Makurdi, Nigeria
solagabriel@yahoo.co.uk

Abstract

Photoperiod manipulation is routinely used in aquaculture industry with the aim to enhance growth in several commercially important temperate fish species. The present study therefore was designed to assess the effect of twenty-four hours of darkness (24D: 00L), twenty-four hours of light (00D: 24L) and the normal day light as the control (12D: 12L photoperiod) on aggressive behaviour and growth response of the fingerlings of tropical African catfish Clarias gariepinus.

Within the six weeks experimental period, it was observed that fish exposed to 24D: 00L photoperiod had the highest maximum and individual weight (P<0.05) while prolonged light hours stressed the fish and caused reduced growth, similarly the weight gain and growth rate was higher in 24D: 00L photoperiod while the specific growth rate were statistically same among the treatments. Feed conversion efficiency (FCE) was 58% better for fish reared in the 24D: 00L compared with those in the 00D: 24L photoperiod system. Aggressive behaviour was quantified as a measure of percentage mortality of the fish, scars on the body of fish and percentage of fish bitten, it was however observed that aggressive behaviour in the African catfish increased as the number of light hour increases with the highest survival rate of 100% being observed in the 24D: 00L photoperiod while 00D: 24L photoperiod had the highest mortality rate of 18%. This study has therefore shown that artificial photoperiod of total darkness could improve food conversion efficiency above 100% and reduce cannibalism.

Key words: African catfish, cannibalism, feed conversion efficiency

Introduction

Environmental and nutritional factors as well as genetic parameters notably influence fish growth. In addition to temperature and other environmental factors, photoperiod is an important factor that affects living organisms including fish. Effects of photoperiod on growth rate and other variables have been studied in various species (Ruchin, 2007). Light and dark alternation is generally thought to be the main synchronizer of feeding activity (Hossain et al 1999). Photoperiod not only affects feeding activity, but also plays a decisive role in growth, survival and social behaviour (Boeuf and Falco 2001). Such influences are caused by physiological mechanisms; such as altered hormone production, which may improve feed conversion efficiency (Purchase et al 2000), however photoperiod requirements are species specific and may vary for each developmental stage.

Stocking density of African catfish has for long been considered the most important factor affecting cannibalism and aggression (Kaiser et al 1995; Almaza´n Rueda 2004). In African catfish, however, aggressive behaviour is also affected by factors other than stocking density such as photoperiod (Almaza´n Rueda et al 2004). As the growing awareness in the society about animal welfare puts increasing demands on the housing conditions in fish farming facilities to enable and develop welfare friendly housing systems, more information is needed on the social behaviour and the factors that can affect the social interactions in fishes, especially in fishes which exhibit aggressive behaviour and cannibalism The present study was therefore designed to assess photoperiod effect on the growth and social behaviour such as aggression on the fingerlings of the African catfish Clarias gariepinus.

Materials and methods

Fingerlings of Clarias gariepinus were obtained through induced breeding from the Department of Fisheries and Aquaculture research farm and acclimatized for two weeks during which they were fed twice daily with 0.8mm Coppens starter feed. The fish were maintained in the re-circulatory system with an average flow rate of 4 litres/minute (dissolved O₂-7.5-11.5 mg/litre; pH 7.1-8.5; water temperature 25-30ºC).

Twenty-five C. gariepinus fingerlings of mean weight of 9.92±0.12g were selected at random weighed and placed in six rearing tanks connected to the water circulatory system. The six tanks were assigned to three photoperiods namely twenty-four hours of light (00D: 24L), twelve hours of light twelve hours of darkness (12D: 12L) and twenty-four hours of darkness (24D: 00L). The light phase was achieved with the aid of an energy bulb (60W) emitting 150 lux intensity of light measured at the surface of water while the dark phase was achieved covering the selected rearing tank with non-heat absolving tarpaulin material.

The fish during the course of the experiment were fed 5% of their body weight with commercial 2mm feed (8.2% moisture, 9.5% ash, 45% crude protein, 12% ether extract, 1.5% crude fiber) and this lasted for 6 weeks of the experiment.  Individual bodyweights were taken at the start and subsequently on weekly basis till the end of the experiment for adjustment of feeding rate of the different photoperiods and growth performance evaluation. Weights were measured to the nearest gram using a sensitive weighing balance.

Specific growth rate (SGR) was calculated as:
    (ln final weight−ln initial weight)/duration of experiment (days)

Feed conversion efficiency was measured by;

    (100*Weight gained)/Feed intake

Aggressive behaviour was difficult to quantify however Almazan Rueda et al (2004) showed that there is a strong correlation between the number of aggressive acts and the number of scars and wounds on the body of African catfish, therefore aggressive behaviour was quantified by counting the number of scars and wounds on the body of individual fish at the end of the experiment and expressed as: 

   
    (Number of scars on fish)/ (Number of fishes that survived).

Percentage of fish bitten was determined by the formula;

    100*(Total number of fish bitten)/(total number of fish at the end of the experiment)

Percentage mortality

   
    100*N_t/N₀                              

Where Nt and N₀ are the numbers of dead fish at the end of the experiment and the initial number of fish stocked at the start of the experiment..

Data were analysed using Genstat Discovery Edition 3 (VSNi 2008).

Results and Discussion

Results from the present study reveal twenty-four hours of darkness (24D: 00L) as the best photoperiod for the rearing of African catfish as increased growth was observed compared to extended periods of light (00D: 24L and 12D: 12L), Similarly the efficiency of food utilization was observe to be greater than 100% for 24D: 00L indicating that feeding fish feed less than a kilogram produced one kilogram of flesh. Similar results were reported by Britzand Pienaar (1992) and Almazan Rueda (2004), as both reported growth rates of African catfish to decline as the length of light period increased. In studies on channel catfish Ictalurus punctatus, a slight tendency for higher growth and somewhat lower food conversion ratios under a 12D : 12L photoperiod was demonstrated by Stickney and Andrews (1971), which is in contradiction to the findings of this experiment. According to Purchase et al (2000), increasing the hours of light per 24 h, has the potential for increasing growth rates without an increase in food consumption in different fish species.  Biswas et al (2006) demonstrated that under long and continuous photoperiods, higher growth rates are assured due to higher food intake and food conversion efficiency, as visual feeder fish requiring light (Cox and Pankhurst 2000). Opposite findings however were observed in the present study with reference to photoperiod as decreasing the light phase increased growth with increasing feed conversion efficiency. Physiological study of the African catfish reveals a relatively small eye per-unit body size compared to other teleost fish; this could however have strong consequence as a contributor to food capture. However, the possession of some adaptive features such as barbels is thought to be one of the important features used in search and capture of food, in line with this conclusion Ali bani (2009) proposed that visual system plays no important role in the feeding activity of paddle fish (Wilkens et al 1997) and sturgeons (Lindberg 1988). They further explain that Sturgeon eyes are very small relative to fish size and probably do not contribute much to the capture of food (Billard and Lecointre 2001). However, the possession of highly specialized organs such as rostrum, ampulla of lorenzini and barbels somehow make them light-independent for feeding. Although Clarias gariepinus is both a nocturnal and a daylight feeder, vision is not considered to be the major factor in search and capture of food (Hecht and Appelbaum 1987). This confirms the preference of African catfish for darkness  as behavioral studies illustrate that avoidance of light and a preference for dark areas are innate behaviour among young Clarias gariepinus (Britz and Pienaar 1992).

Sami (2009) stated that due to the variety of environments inhabited by fish, from temperate to tropical or freshwater to deep seawater, and the resulting high divergence demonstrated in fish physiology regarding biological rhythms in terms of feeding behaviour and locomotor activity (diurnal vs. nocturnal) and reproductive strategies (seasonal vs. continuous spawner), it is therefore difficult to generalize results found in one fish species to all teleost. Hence the variance of the present study compared to those on Tilapia by Abdel-Fattah et al  (2004), Biswas et al (2002) and Biswas and Takeuchi (2002). Abdel-Fattah et al (2004) reported that Oreochromis niloticus fry and fingerling grow better in condition of higher light phase with best weight gain, specific growth rate (SGR), feed efficiency and fish survival observed in 00D: 24L and 6D: 18L. Similarly Biswas et al (2002) and Biswas and Takeuchi (2002) demonstrated that metabolic rate and energy loss were negatively correlated with light periods. Similar observations were also reported in Atlantic salmon by Rottiers (1992) as higher growth rates were observed under longer photoperiod (08D: 16L); also Hanet al (2005) showed reduced growth in Chinese long snout catfish exposed to low (5 lux) or high (443 lux) light intensities, with specific growth rate (SGR) and feed conversion efficiency (FCE) higher in fish exposed to medium light intensities (74 lux). Therefore the difference in the result obtained in the different study compared with those cited above can be attributed to difference in fish species and fish size culture, and the chamber system of production,  and intensity and duration of illumination for the light phase. Hence, photoperiod requirements are species specific and vary for each developmental stage.

Mortality increased as the light phase increased in the present study; similarly, survival rate of 100% was observed in 24D: 00L in the experiment of Almazan Rueda et al (2005) with 98% for 18D:  6L, 98.3% for 12D : 12L and 96.6% for 6D: 18L photoperiod. Also, Appelbaum and Mcgeer (1998) observed a mortality ranging from 5% (95% survival for lesser light phase) to 23% (77% survival increased light phase), in contrast to this Ali Baniet al (2009) reported the highest survival rate (89%) in the 12L: 12D period in juvenile of great sturgeon exposed to 8 weeks of photoperiod at different light phases. The differences in the observed mortality and survival however can be attributed to differences in culture system, intensity of light, duration of light phase, and stage of the fish life cycle. The majority of deaths were un-observed and attributable to cannibalism; cannibalism was concluded to be the cause of the mortality due to the observation of dead fish missing either one or a combination of their barbels, eyes, fins, belly, tail and part or all of the body. In line with this result, Appelbaum and Mcgeer (1998) observed surfaces of dead fish to be missing one or a combination of part or all of the body and attributed it to cannibalism. Cannibalism has been established to be a common feature of nutritionally deficient fish (Smith and Reay 1991) and studies with C. gariepinus have shown that nutritional indices of larvae reared on dry food suggest partial starvation (Segner et al 1993). However, since the fish were fed the same type of diet, then the course of cannibalism and mortality in the fish is attributed to the photoperiod used and that it increases as the light phase increases.

An inverse relationship between feeding rate and cannibalism was found by Hecht and Appelbaum (1987). It could also be concluded that increase in feeding rate as a result of adjustment in growth led to no or less mortality in the fish reared in no light phase (24D: 00L) in accordance with the fact that territorialism struggle among fish was discouraged due to impaired vision caused by reduced light phase (12D: 12L), however a less proportionate increase in feeding rate as well as territorial displacement is the likely course of higher mortality in the 00D: 24L photoperiod. As in other fishes, stocking density of African catfish is considered the most important factor affecting cannibalism (Kaiser et al 1995) and aggression (Almaza´n Rueda 2004). In African catfish, however, aggressive behaviour is also affected by factors other than stocking density such as photoperiod (Almaza´n Rueda et al 2004). The number of scars and wounds on the body of the fingerlings gradually increased from 1.96±0.14 to 3.04±0.23 as the number of light hours increased. Fish at 00D: 24L photoperiod had the highest number of scars and wounds on the body. Almaza ‘n Rueda et al (2005) reported a total range of 1.4 to 2.2 number of scars at various photoperiods; however, the 6D: 18L had the highest number of scars (2.2) and the highest percentage of fish bitten, hence aggression increased as the light phase increases.

Figure 1. Cannibalized fishes from 00D: 24L photoperiod

References

Received 20 June 2012; Accepted 28 September 2012; Published 6 November 2012

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