Introduction

In ornamental high-value species, such as yellow tail cichlid Pseudotropheus acei, discus Symphysodon aequifasciata, electric blue cichlid Sciaenochromis fryerii and blue streak hap Labidochromis caeruleus, emphasis is placed on achieving high levels of skin pigmentation as this is one of the most important quality criteria dictating their market value (Gouveia et al. 2003; Harpaz and Padowicz 2007). High fry quality and survival in the production of ornamental fish is also important. The age and nutritional status of broodstock are the major factors that effect productive and quality of fish eggs (Izquierdo et al. 2001); it is reported that the essential fatty acids, alfa tocopherol, ascorbic acid and carotenoids in fish feeds affect on the stimulation of sexual maturation, enhancement of fertility, egg quality and viability of the juveniles (Scabini et al. 2011). Among these components, carotenoid sources have an important role on the coloration and reproduction performance of fish, and studies have shown that dietary supplementation of carotenoid sources improves the reproduction performance of fish (Vilchez et al. 2011; Watanabe and Vassallo-Agius 2003). Commercial aquafeeds typically contain the natural components like carotenogenic microalgae and krill (Gouveia et al. 2002, 2003; Verakunpiriya et al. 1997) as well as astaxanthin and cantaxin (de la Mora et al. 2006; Kalinowski et al. 2005; Lakeh et al. 2010). Carotenoids may have various biological effects in fish such as provitamin A, immunoenhancement or antioxidation (Izquierdo et al. 2005). The primary sources of color in the skin of aquarium fish are from dietary microalgae, phytoplankton and higher plants. Additionally, micro algae have been used as dietary supplements to enhance health and nutritional performance of a range of fish species. Improvements of growth, feed utilization, lipid metabolism, physiological activity, stress response, disease resistance and carcass quality have been reported with dietary algal inclusion levels of 1–5% (Güroy et al. 2011; Mustafa and Nakagawa 1995). Spirulina is one of the most commonly used micro algae in aquafeeds because of its rich source of protein, vitamins, essential amino acids, minerals, essential fatty acids and carotenoids such as β-carotene, xanthophylls, zeaxanthin, echinenone and cryptoxanthin (Nakagawa and Montgomery 2007).

The effects of Spirulina on fish growth, feed intake, pigmentation and nutrient utilization have been investigated for several fish species (Mustafa et al. 1997; Nandeesha et al. 1998; Palmegiano et al. 2008; Takeuchi et al. 2002). The yellow tail cichlid is popular due to its brilliant colors and because it may be kept in small aquaria (Axelrod et al. 2007). There is no information in the literature on the effects of dietary Spirulina levels on growth, coloration and reproductive performance in yellow tail cichlid. Therefore, the aim of the present study was to determine the effect of dietary Spirulina levels on the coloration, reproductive performance and growth of yellow tail cichlid.

Materials and methods

Fish and rearing conditions

Yellow tail cichlids were obtained from a local commercial aquarium (Zonguldak, Turkey) and transported to the Ornamental Fish Unit of Armutlu Community College, University of Yalova, Turkey. Yellow tail cichlids were randomly distributed among 12 tanks at a density of 10 (2 male and 8 female) fish per tank with three replicate tanks for each dietary treatment. Experimental groups were fed twice daily (0830 and 1630) by hand to visual satiation. The tank flow rate was 3 l min−1, and water quality was monitored daily. Water temperature was maintained at 26.7 ± 0.0°C, dissolved oxygen at 8.1 ± 0.06 mg l−1 and pH at 8.14 ± 0.06. The system was housed in a climate-controlled laboratory with controlled photoperiod (12 h light:12 h dark).

Experimental diets

Spirulina meal was provided by Egert Doğal Ürünler Limited (İzmir, Turkey) (Table 1). Four isonitrogenous (350 g kg−1 crude protein) and isoenergetic (21 MJ kg−1) experimental diets were formulated according to Güroy et al. (2012). A diet with fish meal as the main protein source was used as the control diet (C). The other three diets were formulated incorporating Spirulina at 2.5% (SP2.5), 5% (SP5) and 10% (SP10) of fish meal weight. Fish oil and vegetable oil were used at a 1:1 ratio. The proximate composition of the experimental diets is shown in Table 2.

Table 1 Chemical composition (%) of fish meal, Spirulina meal and dehulled soybean meal
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Table 2 Formulation and proximate composition of experimental diets
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Dietary ingredients were mixed in a food mixer (Dirmak Food Equipment, Turkey, model no: IBT-22) with warm water until a soft slightly moist consistency was achieved. This was then cold-press extruded (PTM P6 extruder, Yalova, Turkey) to produce a 1-mm pellet. The moist pellets were then fan-dried and stored frozen at −20°C until use.

Sampling and chemical analyses

Analysis of crude protein, moisture, lipid and ash in diets and ingredients was performed according to standard AOAC (2000) procedures. Dry matter was determined by drying at 105°C until a constant weight was obtained. Ash content was determined by burning in a muffle furnace at 525°C for 12 h. Crude protein (N*6.25) was analyzed by the Kjeldahl method after acid digestion. Crude lipid was analyzed by the Soxhlet method. Crude fiber was determined by acid/alkali hydrolysis recovering filtered residue and ignition of the dried sample for 3 h. Nitrogen-free extract (NFE) was calculated by taking the sum values for crude protein, lipid, ash and crude fiber and then subtracting this from 100. Dietary gross energy was calculated using the conversion factors of 23.7 kJ g−1 for protein, 39.5 kJ g−1 for lipid and 17.2 kJ g−1 for carbohydrate (Brett and Groves 1979).

Reproductive performance

The reproductive performance of yellow tail fed their respective diet was monitored over 12 weeks. Brooding females were checked for spawning activity daily. Whenever present, eggs were gently removed from the buccal cavity of brooding fish, and the hatching rate monitored over 6–10 days.

Color measurement

Fish were individually weighed and measured for skin color using a Minolta CR-300 Chroma Meter (Minolta Camera Co. Ltd., Asaka, Japan) before commencement of the feeding trial to establish baseline measurements (week 0) and then every 2 weeks for the 12-week period. The measurements were performed on left flanks of body area and caudal region of each fish. The Chroma Meter was set to take absolute measurements in the L* a* b* measuring mode (CIE 1976) using D65 illuminant. L* is the lightness variable (where white = 100 L* and black = 0 L*), a* is the red chromaticity coordinates where +a* stands for red, and −a* stands for green, and +b* is the yellow chromaticity coordinates where +b* stands for yellow, and −b* stands for blue.

Carotenoid analyses

The skin was dissected from the dorsal body area for carotenoid content determination. Total carotenoids were extracted with acetone and quantified spectrophotometrically using the extinction coefficient (E 1%1cm) of 2,100 (Gouveia et al. 1997).

Calculations

Growth performance, in terms of specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) were determined using the following formulae:

$$ \begin{gathered} {\text{Feed Conversion Ratio}}\left( {\text{FCR}} \right) = {\text{FI}}/{\text{WG}} \hfill \\ {\text{Specific Growth Rate}}\left( {\text{SGR}} \right)\left( {\% {\text{ day}}} \right) = 100 \times \left( {\left( {{\text{ln FBW}} - {\text{lnIBW}}} \right)/{\text{T}}} \right) \hfill \\ {\text{Protein Efficiency Ratio}}\left( {\text{PER}} \right) = 100 \times \left( {{\text{WG}}/{\text{PI}}} \right) \hfill \\ \end{gathered} $$

where FBW is the final body weight (g), IBW is initial body weight (g), FI = feed intake (g)WG = weight gain (g), T = time (days) and PI = dietary protein intake (g).

Statistical analysis

All data were subjected to a one-way analysis of variance (ANOVA), when a significant difference was found among treatments; Duncan’s multiple range test was performed to rank the groups using Statgraphics 4.0 (Manugistics Incorporated, Rockville MD, USA) statistical software (Zar 2001). All values were considered significant at the 5% level.

Results

The growth and reproduction parameters for yellow tail cichlid fed increasing levels of Spirulina are shown in Table 3. The survival rate was 100% for all treatments. Mean final weight ranged from 7.31 g (C) to 8.56 g (SP10) and was significantly lower in fish fed diet C than all Spirulina diets. Furthermore, the final mean weight (FMW) and specific growth rate (SGR) of fish fed diet SP10 were not significantly different compared to fish fed SP2.5 and SP5 diets. All the experimental diets were well accepted by fish; furthermore, feed intake (FI) tended to elevate with increasing dietary Spirulina level, and fish fed diet SP10 (12.50 g fish−1) had significantly higher FI values compared to fish fed diet C (9.63 g fish−1). No significant differences in feed conversion ratio (FCR) were observed among these groups. Although the protein efficiency ratio (PER) of group C was lower than that of all Spirulina diets, these differences were not significant (P > 0.05).

Table 3 Growth and reproduction performance of yellow tail cichlids after 12 weeks of feeding on experimental diets
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Dietary Spirulina significantly affected the total egg production (TEP) of the yellow tail cichlid and the subsequent hatching rate (%) of the eggs (Table 3). The TEP of yellow tail varied from 101 to 346, with the all Spirulina groups superior (P < 0.05) than those fed the diet C. Additionally, the TEP was higher in fish fed with the SP2.5 (346) diet than in diets SP5 (231) and SP10 (191). The eggs from fish fed all Spirulina diets displayed significantly higher hatching rates compared to the eggs from fish fed diet C (P < 0.05). Although hatching rate tended to decrease with increasing dietary Spirulina level, no significant differences were observed among these groups (P > 0.05).

There were significant effects of experimental diets on lightness (L) values in the body area (Table 4) and in the caudal region (Table 5). The skin of fish fed diets containing Spirulina had significantly lower lightness values than fish fed the control diet in the both caudal and body regions. Red/green tonality (a) of skin from the body varied from 1.56 (C) to 2.27 (SP5), with the highest values being found in fish fed the Spirulina diets. The red/green tonality (a) of skin from the body of fish fed diet SP2.5 (2.05) was not significantly different compared to fish fed the SP5 diet (2.27). The yellow/blue tonality (b) in the body was not affected by the concentration of Spirulina in the diet (P > 0.05). However, the yellow/blue tonality (b) in the caudal region was elevated with increasing dietary Spirulina levels, and fish fed diet SP10 (−8.17) had significantly higher the yellow/blue tonality (b) values compared to fish fed diet C (−6.88). The highest carotenoid concentrations in skin were obtained in diets supplemented with Spirulina (1.47–2.30 μg g−1) (Fig. 1) (P < 0.05).

Table 4 Color parameters (L, a, b) in body of yellow tail cichlid fed experimental diets for 12 weeks
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Table 5 Color parameters (L, a, b) in caudal region of yellow tail cichlid fed experimental diets for 12 weeks
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Fig. 1
figure 1

Total carotenoid of skin of yellow tail cichlids after 12 weeks of feeding on experimental diets

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Discussion

The present study is the first study to evaluate Spirulina in diets for yellow tail cichlid. The current investigations were performed to test the feasibility of including dietary Spirulina meal in practical diets for yellow tail cichlid. In the nutrition trial, supplementation of Spirulina had clear beneficial effects on the growth, skin coloration and reproduction performance of yellow tail cichlid. The SGR of fish fed all Spirulina diets were significantly higher compared to the non-Spirulina supplemented diet (C). Because Spirulina is rich in proteins, vitamins, minerals, essential amino acids and fatty acids (Nakagawa and Montgomery 2007), it has been identified as a potential feed ingredient for cichlids and ornamental fish and appears to be a promising dietary ingredient. Numerous studies have shown that dietary Spirulina can affect the growth performance of various cichlid and non-cichlid fish species. For example, in cichlids, it has previously been reported that 20% (Ungsethaphand et al. 2010) and 40% (Olvera-Novoa et al. 1998) of FM can be replaced with Spirulina without detrimentally affecting the growth performance of tilapia Oreochromis mossambicus. Furthermore, James et al. (2006) reported that dietary inclusion of 8% Spirulina significantly elevated growth performance of the ornamental red swordtail Xiphophorus helleri. The present study is in agreement with the prior reported cichlid and ornamental studies and illustrates the possible use of Spirulina as a partial substitute for FM in yellow tail cichlid diets.

To the authors’ knowledge, there is no information about the effects of dietary Spirulina meal on reproductive performance of cichlids; however, James et al. (2006) reported that dietary Spirulina elevated red swordtail reproductive performance. In the present study, reproductive performance of yellow tail cichlid also increased with the dietary supplementation of Spirulina meal; the highest TEP and hatching rate was observed in the SP2.5 diet, but there were no significant differences among the Spirulina diets in terms of hatching rate. The reason for this elevation in reproductive performance is not fully understood, but previous studies have shown that reproductive performance can be modulated by dietary carotenoids (Watanabe and Vassallo-Agius 2003), which may be mediated through various biological responses to the elevated dietary provision of provitamin A, protection from adverse lighting conditions, promoting chemotaxis of spermatozoa or antioxidant functions (Izquierdo et al. 2005). An improvement in reproductive performance in response to elevated inclusion of dietary carotenoid sources has been previously reported in gilthead seabream Sparus aurata (Scabini et al. 2011), yellow tail Seriola quinqueradiata (Vassallo-Agius et al. 2001, 2002) and rainbow trout Oncorhynchus mykiss (Dabrowski et al. 1987).

Dietary carotenoids do not only have functional roles in modulating reproductive processes, but also, as is well documented, carotenoids are utilized in diets to induce coloration. In the present study, the diet containing the Spirulina meal was the most successful in inducing the yellow and blue coloration in the skin of the yellow tail cichlid. Spirulina meal has also been used successfully to increase the skin coloration of red tilapia (Matsuno et al. 1980), red sword tail (James et al. 2006), blue gourami, Trichogaster trichopterus (Alagappan et al. 2004) and goldfish, Carassius auratus (Gouveia et al. 2003; James et al. 2009). Moreover, Ako et al. (2000) reported diets containing 1.5–2.0% of a carotenoid-rich strain of Spirulina platensis, and 1% of Haematococcus pluvialis significantly enhanced coloration of red velvet sword tail, rainbow fish Pseudomugil furcatus and topaz cichlids Cichlasoma myrnae. Indeed, Spirulina is a well-recognized carotenoid source, containing high levels of xanthophyll, β-carotene and zeaxanthin, and dietary inclusion of Spirulina has been reported to affect fish pigmentation (Gouveia et al. 2003; Nandeesha et al. 2001). The skin coloration changes observed in the present study were confirmed by the observed elevated total carotenoid levels (μg g−1) in the skin of yellow tail cichlids fed dietary Spirulina meal.

The results clearly show that Spirulina meal could be used in yellow tail cichlid diets to replace up to 10% of the dietary fish meal without causing any adverse effects on growth, reproductive performance or coloration. Indeed, all fish fed with Spirulina diets exhibited higher growth values and broodstock performance. Spirulina meal clearly offers much potential for inclusion in diets for yellow tail cichlids, and this preliminary study confirms a basis for more extensive investigations.