The morphological aspect of a brown tilapia compared to that of the Nile tilapia ( Oreochromis niloticus )

. Brown tilapia is the descendant of long-finned ornamental tilapia. This is a new kind of tilapia with normal-sized fins. Thus, it is not suitable as an ornamental fish. Despite this, the feasibility of brown tilapia for food fish should be evaluated. The present study aimed to investigate the morphological aspects of brown tilapia in terms of morphometric, meristic, length-weight relationship, condition factor, morphological abnormality, and fluctuating asymmetry compared to those of the NIRWANA Nile tilapia ( Oreochromis niloticus ) which commonly cultured in Indonesia. The observations were undertaken at the end of the grow-out phase. The grow-out phase was conducted for four months, while the larval rearing and nursery phases were previously conducted for two months. The results showed that, except for the color, the brown tilapia could not be morphologically differentiated from NIRWANA Nile tilapia. The brown tilapia's length-weight relationship and condition factor were similar to those of the NIRWANA Nile tilapia. As such, in NIRWANA Nile tilapia, the brown tilapia exhibited some fluctuating asymmetry with no morphological abnormality. Those overall results suggested that the brown tilapia was considered to have the potential to be developed as a new kind of tilapia food fish.


Introduction
Tilapia is one of the most economically essential fishes cultured in Indonesia [1].Recently, the popularity of tilapia as a local food fish has continuously increased, assigned by increasing the price in the market; hence, the price is higher than other economically important fishes in the Indonesian market, like common carp (Cyprinus carpio), African catfish (Clarias gariepinus) and striped catfish (Pangasianodon hypophthalmus) (pers.obs.).The kind of tilapias cultured in Indonesia, either as a pure species of Nile tilapia (Oreochromis niloticus) or hybrids with Mozambique tilapia (O.mossambicus) and blue tilapia (O.aureus), mostly had a grey color (known as black) and red color [2].On the other hand, there are also different colors in tilapias; one is brown.Originally, the brown tilapia was a kind of ornamental fish with long fins.However, the brooders of this ornamental tilapia also produce brown-colored tilapia with normal (not long) fins.Thus, this brown-colored tilapia is unsuitable (not attractive) for ornamental fish purposes and is supposed to be more suitable for food fish.Also, this brown tilapia is quite similar to the brown color of giant gourami (Osphronemus goramy), one of Indonesia's most expensive freshwater food fishes (pers.obs.).
To date, report or scientific publication about brown-colored tilapia is scarce.The report related to the brown-colored tilapia has only been published by Basavaraja & Raghavendra [3], who reported that mating between Mozambique tilapia (O.mossambicus) and red hybrid tilapia (Oreochromis sp.) might produce a brown-colored tilapia.However, it is unknown if the brown-colored tilapia and brown-colored tilapia resulting from longfinned ornamental tilapia are the same since, based on the given picture, both browncolored tilapia exhibited a different color (pers.obs.).
Since brown tilapia is a new kind of tilapia, extensive studies are needed to characterize and evaluate the feasibility of being developed as a new candidate for food fish to increase the diversification of the tilapia cultured in Indonesia.The present study was conducted to explore a morphological aspect of the brown tilapia in terms of morphometric, meristic, length-weight relationship, condition factor, morphological abnormality, and fluctuating asymmetry, as compared to those of the Nile tilapia (O.niloticus) commonly cultured in Indonesia.

History of the brown tilapia
Brown tilapia examined in the present study were descendants of long-finned brown tilapia originally collected from a governmental fish hatchery of Kediri Regency, East Java Province, in late July 2016, together with the collection of long-finned red (with black blotches) tilapia.Those long-finned tilapias (ten juveniles each of 5-7 cm standard length) were stocked together within a concrete tank (4×3×0.7 m) at the Research Institute for Fish Breeding (RIFF) Sukamandi, Subang Regency, West Java Province.Besides producing red-and grey-colored tilapias with long and normal fin lengths, during 2017 and after that, those long-finned tilapia brooders (Figure 1A and 1B) produced colored tilapia with both long fins and normal fins.Those fishes were usually grown up and used either for ornamental fish or food fish at RIFF Sukamandi.
In early June 2022, the last descendants of brown tilapia with normal-sized fins consisted of 12 males and 36 females (body weight of about 250-350 g) were plotted for mating within four concrete tanks (4×3×0.7 m); each tank was stocked with three males and nine females (sex ratio one male: 3 females).As a comparison, an equal number and body weight of brooders of a superior grey-colored Nile tilapia strain, namely NIRWANA Nile tilapia, were also plotted for mating within four other concrete tanks.In late June 2022, larvae from each concrete tank were harvested; 200 larvae were each taken randomly, then stocked into separated happas (1×1×0.7 m) placed within an earthen pond (15×15×1 m) and reared for two months.At the end of the month's nursery phase, 20 juveniles from each happa were randomly taken (160 juveniles in total) and stocked into a concrete tank (4×3×0.7 m).These juveniles were grown up for the subsequent four months of the growout phase to the end of December 2022.Then, the morphological aspects of the brown tilapia (Figure 1C) in terms of the morphometric, meristic, length-weight relationship, condition factor, morphological abnormality, and fluctuating asymmetry were characterized and compared to those of the NIRWANA Nile tilapia (Figure 1D).

Morphometric and meristic characterizations
As a new kind of tilapia, the taxonomic status of brown tilapia is unknown and needs to be resolved.Awaiting the next molecular characterization using the whole genome sequencing technique as previously performed for the Sukamandi tilapia strain [4], a biometric morphology approach was first conducted as an attempt to assess the taxonomic status of brown tilapia based on the morphological characteristics.The biometric characterization was conducted through the measurement of 24 morphometric characters (Figure 2), as conducted by previous workers in the morphological characterizations of Nile tilapia (O.niloticus) populations in the African waters [5,6].As well as conducted in previous studies [5,6], the numbers of gill rakers on the first branchial arch, pectoral fin rays, dorsal spines, dorsal fin rays, pelvic spines, pelvic fin rays, anal spines, anal fin rays and lateral line scales series (upper and lower) were counted for meristic characterization.The data obtained were then subjected to a principal component analysis (PCA) to define possible differences.

Length-weight relationship and condition factor analysis
The growth performance is an important aspect of aquaculture, especially for food fish.
Awaiting the following more complete evaluation of the growth performance, the specific growth rates of brown tilapia and NIRWANA Nile tilapia during the grow-out phase in the present study were recorded.The growth pattern of brown tilapia in the present study was also assessed using a length-weight relationship compared to that of the NIRWANA Nile tilapia.In addition, the growth pattern related to the morphological aspects of brown tilapia compared to the NIRWANA Nile tilapia was also assessed using a condition factor index.The lengthweight relationship and condition factor analysis were performed based on the total length (L) and body weight (W) at the end of the grow-out phase.The length-weight relationship was analyzed based on the power regression of W = aL b , where a was the constant and b was an exponent [7].While the condition factor was analyzed using Fulton's condition factor (K) as follows: K = (W/L 3 ) ×100 [7].

Morphological abnormality and fluctuating asymmetry observations
Since the brown tilapia examined in the present study were the descendants of a limited number of long-finned brown tilapia brooders, some degree of inbreeding might occur during the natural breeding in producing them.A high level of inbreeding results in morphological abnormality and developmental instability of morphological characteristics, commonly referred to as a fluctuating asymmetry.Thus, the brown tilapia's morphological abnormality and fluctuating asymmetry should be investigated to reveal if the inbreeding level had detrimental effects related to the morphological aspect.The Morphological abnormalities of brown tilapia and NIRWANA Nile tilapia in the present study were observed according to morphological abnormalities previously reviewed for tilapia [8].Then, the fluctuating asymmetry of brown tilapia was measured for the number of pectoral fin rays, pelvic fin rays, and gill rakers on the upper and lower first branchial arch, upper lateral line scales, and lower lateral line scales, as has also been conducted by previous workers for Nile tilapias [9][10][11][12][13].The fluctuating asymmetry in the present study was recorded for those characters in terms of the number and magnitude [14].

Results and discussion
The mating between male and female brooders of brown tilapia with normal (not long) fins produced progenies of normal-sized fins.However, not all of them had a brown color; some of them were grey (the normal color for tilapias).While the inheritance of red and black body color in tilapia has vastly been reported for many years [15,16], the brown color inheritance in tilapia has only recently been reported by Basavaraja & Raghavendra [3].However, the color pattern of their brown tilapia differed from that of the brown tilapia examined in the present study.Based on the photograph, their brown tilapia had a redbrownish body color with scattered dark blotches on the upper head and upper front body parts, while the lower parts were lighter.Whereas brown tilapia examined in the present study had an intense dark brown color in the almost whole head and body, with either somewhat light brown or golden yellow in the partly lower head and body (Figure 1).Since this difference, the brown color inheritance of brown tilapia examined in the present study should still be investigated later to confirm whether the brown color inheritance of both brown tilapias is the same.
The brown tilapia in the present study exhibited vertical dark stripes in the caudal, dorsal, and anal fins and on the body.This striping pattern was similar to that of the NIRWANA Nile tilapia.Vertical dark stripes have been reported as the main characteristic of Nile tilapia species [5].Based on the striping pattern, brown tilapia in the present study was thought to belong to the species of Nile tilapia (Oreochromis cf.niloticus).Based on the striping pattern, the brown tilapia observed in the present study was likely not a hybrid between Nile tilapia and Mozambique tilapia since the hybrid between the two species was reported as having stripes on the caudal fin without markings on the body, and some individuals had marked on the body without stripes in the caudal fin [17].
At the end of the grow-out phase, the body weight of brown tilapia averaged 121.6±32.0g, and the specific growth rate accounted for about 2.3%/day.At the same time, the final body weight of NIRWANA Nile tilapia was 158.7±35.0g, with a specific growth rate of about 2.5%/day.Those results suggested that the growth performance of brown tilapia was relatively inferior compared to the superior strain of Nile tilapia commonly cultured in Indonesia.This is due to NIRWANA Nile tilapia's growth performance improved via a selective breeding program [18], thus passing the prerequisite determined by the Ministry of Marine Affairs and Fisheries, Republic of Indonesia, to be released as a superior strain.In the future, a genetic improvement of the brown tilapia should be conducted to increase the growth performance.
The morphometric data of brown tilapia and NIRWANA Nile tilapia obtained in the present study was presented in Table 1.Then, a scatter plot of the second and third principal components scores resulting from a principal components analysis performed on the morphometric characters was presented in Figure 3.The results showed that morphometric characters of the brown tilapia and NIRWANA Nile tilapia overlapped.Those suggested that brown tilapia could not be morphometrically differentiated from NIRWANA Nile tilapia.This morphometric characterization supposed that brown tilapia might be a Nile tilapia species (Oreochromis cf.niloticus).Fig. 3. Scatterplot of scores resulted from a principal component analysis performed on the morphometric characters of brown tilapia (○) and NIRWANA Nile tilapia (Oreochromis niloticus) (Δ) along the second (PC2) and third principal component (PC3) axis of the NIRWANA Nile tilapia.In general, the meristic characteristics of both tilapias were in accordance with the meristic characteristics of Nile tilapia species reported from African water by previous workers [5,6], as well as with the meristic characteristics of Nile tilapia from other regions [11,[19][20][21].Those also suggested that both tilapias might belong to the species of Nile tilapia.The length-weight relationship of brown tilapia and NIRWANA Nile tilapia observed at the end of the grow-out phase in the present study was presented in Figure 5.As in NIRWANA Nile tilapia, the length-weight relationship of brown tilapia exhibited a negative allometric (the values of exponent b < 3).That length-weight relationship implied that the body shape of both tilapias became relatively slender with the length increase.These b exponential values of the length-weight relationship were within the range of 2-4 recommended for fishes [7].Overall, the length-weight relationships in Nile tilapia species were reported differently, either as positive allometric (b > 3), negative allometric (b < 3), or isometric (b = 3).The Nile tilapia cultured in Bangladesh [19], Myanmar [20], India [22], Tanzania [23], and Zambia [24] were reported to have negative allometric growth of the length-weight relationship.In contrast, the Nile tilapia cultured in Thailand [25] and Kenya [26] had positive allometric ones.At the same time, a Nile tilapia broodstock in Kenya was reported to have positive allometric growth for females and negative allometric for males [27].On the other hand, a Nile tilapia cultured in Ghana had a nearly isometric growth pattern of length-weight relationship [28].
The mean condition factor of brown tilapia at the end of the grow-out phase was 2.28±0.18,while in the NIRWANA Nile tilapia, it was 2.45±0.22.Those condition factors were not significantly different (P>0.05).The condition factor values that exceeded one suggested that both tilapias examined in the present study were in a good welfare condition.In addition, the condition factors of both tilapias were in accordance with those reported in the previous studies of cultured Nile tilapia, which generally ranged around 1-3 [19,23,[26][27][28][29].
Based on the present study's morphological observations, no morphological abnormality was found in all individuals of the brown tilapia observed.Similarly, all NIRWANA Nile tilapia observed also exhibited a normal morphology.These results implied that inbreeding that might have occurred in producing the brown tilapia used in the present study was still acceptable since it has no detrimental effects on the morphological aspects.Whereas inbreeding levels of 12.5% and 25% occurred in Nile tilapia have been reported to have detrimental effects (inbreeding depression) regarding morphological deformity [10].3).Out of the number of pectoral fin rays, pelvic fin rays, lateral line scales (upper and lower series), and the gill rakers (upper and lower), only the pelvic fin rays exhibited no fluctuating asymmetry.The fluctuating asymmetry has also been reported in another Nile tilapia cultured in Indonesia and other countries [9,[11][12][13]30].

Conclusion
The present biometric-morphological study suggested that brown tilapia is thought to belong to a Nile tilapia species (Oreochromis cf.niloticus).Its length-weight relationship and condition factor are similar to those of a strain of Nile tilapia commonly cultured in Indonesia, with rather inferior growth performance, suggesting its potency to be developed as a new tilapia food fish, which requires a selective breeding program to improve the growth performance.

Fig. 4 .
Fig. 4. Scatterplot of scores resulted from a principal component analysis performed on the meristic characters of brown tilapia (○) and NIRWANA Nile tilapia (Oreochromis niloticus) (Δ) along the first (PC1) and second principal component (PC2) axis

Fig. 5 .
Fig. 5.Total length (L) and body weight (W) relationship of brown tilapia (○) and NIRWANA Nile tilapia (Oreochromis niloticus) (Δ) at the end of the grow-out phase In terms of fluctuating asymmetry, both brown and NIRWANA Nile tilapias in the present study exhibited some fluctuating asymmetry (Table3).Out of the number of pectoral fin rays, pelvic fin rays, lateral line scales (upper and lower series), and the gill rakers (upper and lower), only the pelvic fin rays exhibited no fluctuating asymmetry.The fluctuating asymmetry has also been reported in another Nile tilapia cultured in Indonesia and other countries[9,[11][12][13]30].

Table 3 .
Fluctuating asymmetry of the brown tilapia and NIRWANA Nile tilapia (Oreochromis niloticus)