Analysis of morphometric and meristic characteristics of three cichlid species in central Iraq: farmed and wild

Unintended or deliberate releases of aquaculture-generated fish into the feral have sparked unease among fishery experts (Ryman et al., 1995; Youngson et al., 1991). Even though such exercises (purposeful) are regularly accomplished to assess the decline yield triggered by human-stimulated habitat destruction, a selection of feasible habitat impairments could be concurrent with this application (Bostanci et al., 2021). First, providing larger numbers of fish in a controlled spot will disrupt the inhabitants’ mass, at least primarily. This may disrupt the density-dependent characteristics of the fish or the habitat (Elliott, 1990). Changes in the amount of food available, the existence of competitive contacts, or the reaction of predators are all examples of factors that may affect the development and presence of wild fish. Aquaculture system fluxes may be a clue to seasonal changes in group strength, according to theoretical beliefs (Fagen & Smoker, 1989). Second, aquaculture fish may differ from feral fish in terms of external characteristics or genetics. Such differences might disrupt the cooperation between feral and given fish, which would subsequently lead to an impact on providing outside of those areas due to obvious density dependence.

Researchers widely used morphometric and meristic features to identify fish species (Turan et al., 2004), as they continue to be the most straightforward methods for distinguishing different species. Evidence from previous studies suggested that morphological variation in meristic traits is the most common way to classify fish (Bronte et al., 1999; Creech, 1992; Hockaday et al., 2000; Mamuris et al., 1998). Researchers, frequently used statistical procedures to split and group fish (Agnew, 1988; Avsar, 1994). Swain and Foote (1999) noted that using methods that directly study biochemical or molecular differences in heredity, such as traditional strategies, is still very important for understanding how populations differ. Changes in a species’ morphometric and meristic characteristics from different locations might result in changes to its genetic makeup and territorial problems that influence the genotype, or both at the same time (Parish & Sharman, 1958). While changes in ecological sources affect morphometric and meristic features equally, these responses might vary depending on the situation and can display species-specific changes.

Phylogenetics and studies on group genetic evolution rely heavily on analyses of morphometric and meristic differences and irregularities in fish groups. According to Turan et al. (2006), many years of introducing and domesticating a fish species— especially one that comes from the wild—means that it has adapted well to a wide variety of geographical locales, which in turn causes phenotypic alterations in the progeny populations. The cause might be environmental variables or hybrids created by extensive inbreeding (El-Serafy et al., 2007; Lehoczky et al., 2025).

For three main reasons, domesticated fish could look different from their feral species. First, since fish have very flexible exterior characteristics, the breeding process may significantly alter their shape (Pakkasmaa, 2000). Second, the strength and route of selection vary between aquaculture and wild fish, which is why they could differ. Third, the use of non-wild fish for provision is one reason why farmed fish might differ from wild ones. Fortunately, the practice of releasing non-wild fish has declined, and the potential consequences of territorial modifications are increasingly recognized (Taylor, 1991). Similar to what has happened with economically viable farmed fish, planned artificial selection may likewise cause genetic alterations in populations of cultured fish (Einum & Fleming, 1997; Fleming & Einum, 1997). Fish that originate from aquaculture facilities are usually confronted with circumstances very different from those faced by their feral equivalents, which might lead to behavioral, morphological, and physiological changes (Beecham et al., 2007). One of the first natural facts provided by Hanson et al. (2007) is the association between morphology and the swimming event. For many fish and other aquatic animal species, swimming performance is the most important trait determining ability (Plaut, 2001).

People widely exploit the remaining species of cichlids in aquaculture around the world and sell them as high-protein food fish internationally. Researchers believe that almost 4000 years ago, the Egyptians were the pioneers of tilapia farming. After being considered for cultivation in the Far East in the late 1940s, a number of tilapia species were eventually transported to the Americas a decade later (Gupta & Acosta, 2004). For many reasons, including its adaptability to a wide range of salinities, its high tolerance to organic pollutants and low levels of dissolved oxygen in water, and its resistance to diseases, tilapia have achieved great success in the aquaculture sector (Cruz & Ridha, 1994). Moreover, as shown by their biology, these fish have a short food cycle, are delicious, and can convert leftover food and waste into excellent protein sources (Galemoni de Graaf and Huisman, 1999; Penña-Mendoza et al., 2005; Yi et al., 1996).

Unlike other nations (Barriga-Sosa et al., 2004), Iraq has not been informed when or how the tilapia species would be introduced. Coad (1996) believed that the tilapia species had made their way to Iraq from Syriavia the Euphrates River. Reports of three tilapia species in Iraq’s southern and central regions date back to 2007. No tilapia from northern Iraq has been reported as of yet. The first tilapia species documented in Iraq is C. zillii, which was gathered from two locations on the waters of the Euphrates by Saleh (2007). O. aureus was detected by Mutlak and Al-Faisal (2009) in Basra City’s major outfall drain (3rd River), located in southern Iraq. Al-Faisal and Mutlak (2015) recently documented O. niloticus in Iraq’s Basrah region. Based on findings in two different locations—the third river outflow drain in Basra City (Mutlak & Al-Faisal, 2009) and the Al-Delmj Marsh in the country’s central region (Al-Zaidy, 2013)—C. zillii seems to be the most prevalent tilapia species in Iraq. Although many authors in Africa have already compared the morphology of cultured and wild tilapia stocks (e.g. Anane-Taabeah, 2019; El-Zaeem et al., 2012; Hassanien et al., 2011; Ikpeme et al., 2017; Jawad et al., 2020; Ndiwa et al., 2016; Teugels & Vreven, 1997; Tibihika et al., 2020), such studies are conspicuously absent for tilapia species in Iraq.

This research aimed to study the morphological and meristic characteristics of three cichlid species in central Iraq—C. zillii, O. aureus, and O. niloticus— caught from two different environments (wild and farmed). Accurate fisheries management and resource optimization rely on morphometric and meristic data. This will be useful for developing further strategies for the production and preservation of these species. The results of this study will also highlight the problems caused by the accidental and deliberate release of farmed fish into the wild, which may have a negative impact on populations of wild fish. The findings will be of particular importance to Iraqi decision-makers.

All morphometric characteristics of the three species showed differences between those raised in aquaculture and those found in the wild, with the wild specimens being shorter overall than the aquaculture ones (Table 1). Therefore, the boxplot of meristic characteristics in Figs 1 and 2 indicated that NDFR, NAFR, and NPFR values were higher in the aquaculture habitat for all species except NPFR for C. zillii and NPFR for O. aureus (Fig. 2). For NGR, LLS, and NV, all counts were higher in aquaculture specimens (Fig. 3). Since none of the meristic traits overlapped (Figs 2 and 3), it was possible to distinguish between the fish from the two habitats using any variable. Consequently, all morphometric and meristic characteristics showed substantial habitat-to-habitat changes (p < 0.01) (Tables 1 and 2).

Figure 2

Boxplot. Samples from farmed and wild cichlids of three species: C. zillii, O. aureus, and O. niloticus were analyzed for three meristic characters: NPFR, NDFR, and NAFR. The mean ± standard error for each character was calculated. NAFR, number of anal fin rays; NDFR, number of dorsal fin rays; NPFR, number of pectoral fin rays.

Figure 3

Boxplot. Three meristic characteristics (number of gills rakers on the first gill arch [NGR], NV, and number of LLS) and for both wild and farmed specimens of three cichlid species (O. niloticus, C. zillii, and O. aureus) are shown by the mean ± standard error. LLS, scales on the lateral line; NGR, number of gill rakers; NV, number of vertebrae.

In Figs 1 and 2, in the boxplots for all variables, it is observed that neither in the medians, quartiles, nor for the whiskers was there overlap. The variability was greater for specimens from aquaculture, where it was observed, for example, for O. aureus and for O. niloticus, than for the NGR, LLS, and NV variables, with quartiles showing bias towards higher values, as well as whiskers. The rest of the variables show very low variation.

The cross-validated discriminant analysis using morphometric characters from all 896 specimens correctly classified 93.9% by variant of each species (Wilk’s lambda = 2.63 E–8, p < 0.001). The lowest classification rate, 73.0%, was achieved using samples from Oreochromis niloticus from the wild (OAW), while samples from C. zillii from aquaculture and wild were the best, with a validated correct classification of 100.0, as well as O. aureus and O. niloticus from aquaculture (Table 2). Cross-validated analysis misclassified specimens from wild O. niloticus, where 8.4% were misclassified with O. niloticus from aquaculture (Table 2).

It is widely believed that fish, being aquatic creatures, are particularly vulnerable to environmental and genetic influences on their external characteristics (Currens et al., 1989; Wainwright et al., 1991). Scientists have found that both types of influences affect fish’s appearance. Conversely, factors beyond genetics and the environment, such as nutrition, have been found to modify the exterior features of crucian carp, Carassius carassius (L.), or enhance predator resistance, while optimal nutritional conditions have been noticed to induce a deeper body morphology in this species (Brönmark & Pettersson, 1994).

The three cichlid species studied were from the aquaculture facility and the wild. The samples from the first group, which lived in nature, were completely different from the samples from the second batch, which dwelt exclusively in the tanks. The disparities in the habitats induced dissimilarities in various morphological characteristics within the two lots of fish, which might indicate that such deviations are caused by ecological impacts, distinctions in the hereditary framework, or both.

Even so, disparities between feral and cultivated groups were primarily the outcome of habitat differentiations. Former reports demonstrated the main part of circumstances acting in morphological distinction among groups of inherently identical fish (Kinsey et al., 1994; Ryman et al., 1984).

Jawad et al. (2020) investigated the meristic features of the cichlid species O. niloticus, which is native to the Republic of Benin in West Africa, in an introduction study. A total of 5 meristic and 10 morphometric characteristics were determined and tallied in this investigation. In both the wild and farmed O. niloticus populations, the values of 6 for the number of pelvic rays and 31 for the number of scales on the LL were invariable. There was no significant difference in the NPFR (p = 0.814), anal fin rays (p = 0.328), and dorsal fin spines (p = 0.255) among the three other estimates. These three meristic traits had extremely comparable values.

Numerous morphological attributes (i.e., body color, size, and shape), behavioral issues, and immunological (changes in chief histocompatibility intricate), biochemical (isoenzymes), and molecular simple sequence length polymorphism (SSLP) (Sharp et al., 2002) attributes have been enjoyed recognizing distinct inbred stocks. Yet, different from other attempts, morphological assessment proposes substantial sums of records in a brief time with no need for utilizing advanced talent or costs. Combined with the use of box plots by regions (habitats) vs. the parameters used in the current study, complete partitioning of wild and cultivated groups with significant changes in external features was noted. This finding proves that this technique is a convenient means for distinguishing between groups of the three cichlid species explored. Moreover, the nine body characteristics utilized in the current assessment played a major part in morphological discrimination.

This study found that compared to the wild group, samples from the aquaculture facility group had larger values for all nine body proportions. Possible causes of these differences between the two species’ habitats include different water temperatures, turbidities, food availability, and water depths and flows. Specifically, variations in turbidity among the aquaculture establishment and the natural environment may have caused the increased eye dimension in the samples from the aquaculture facility group (Matthews & Robison, 1988). This was probably a significant habitation preference, which Aleev (1969) linked to the location of the eyes in the skull. These morphological discrepancies may possibly have originated from the discriminating rearing procedures utilized in aquaculture, inherited drift after establishing cohorts, or the distinct source of fish utilized in breeding groups (Karaiskou et al., 2009). Likewise, the aquaculture group’s estimations of the meristic traits were higher than those of the feral group. This suggests that it was possible to distinguish between the two groups. Furthermore, there seemed to be intraspecific variances since the two groups’ meristic estimation trends were not equal or similar.

The present investigation onto the evaluation of the three cichlid species’ wild and farmed populations uncovered differences in meristic traits and highlighted the most prominent distinctions between the two sets of fish. In the feral group, the range of modification in meristic characteristics, such as the NDFR, anal fin rays, NGR on the 1st gill arch, number of scales on the LL, and NV, was higher in the samples attained from the aquaculture facility than those of the feral groups of the three cichlid species searched. In addition, the number of pectoral fin ray counts was observed to be higher also in the aquaculture samples of C. zillii than in those from the feral group of the same species (Table 1). Matsuoka (1987) and Boglione et al. (2003) stated results regarding these characteristics. The discrepancies in the range of the meristic attributes are believed to be impacted by both ecological and inherited issues (Foote et al., 1999); even so, in certain examples, various researchers (Davidson et al., 1985; Hedgecock et al., 1989; Kinsey et al., 1994; Shepherd, 1991) associated such inconsistencies primarily with habitat influences and phenotypical flexibility (Lindsey, 1981; Stearns, 1989; Swain & Foote, 1999; West-Eberhard, 1989).

The aquaculture group of the three cichlid species’ morphological characteristics deviated from the familial model, as shown by the feral group, the body proved to be more powerful with more fin rays. This shift in body durability is in contrast to findings from research on marine-farmed salmon, where a reversal tendency toward feral fish was seen and deemed to be mostly caused by environmental factors (Fleming et al., 1994; Swain et al., 1991; Taylor, 1991). This could be attributed to the various methods of raising fish. Conversely, to the feral group of the three cichlid species, the aquaculture group fish were raised throughout their lifetimes and at no time came into interaction with the natural habitat. Likewise, they were put through a controlled, artificial variety test that focused on weight for fast development (Gjedrem et al., 1988), which possibly caused a noticeable change in depth (Gjerde & Schaeffer, 1989).

Since there were no previous investigations on the morphological and meristic attributes of the aquaculture and feral groups of C. zillii and O. aureus and investigations only exist on O. niloticus, discrepancies in fin morphological attributes of the aquaculture group of O. niloticus were likewise stated by other researchers (Anane-Taabeah, 2019; Ikpeme et al., 2017; Jawad et al., 2020; Tibihika et al., 2020). Non-interfering swimming diversification associated with unnatural selection likely followed significant degrees of fin nibbling (Abbott & Dill, 1985) and abrasion (Bosakowski & Wagner, 1994).

Enhanced food availability may have directly affected changes in the outward characteristics of the three cichlid species’ aquaculture groups. The lack of predators in aquaculture facilities (Einum & Fleming, 1997; Johnsson et al., 1996) may have changed the focus to food opposition since selection against predator-vulnerable species has been loosened. The basis of such discrepancies in anti-predation actions may perhaps have been increased via development hormone discharge, and consequently, desire for food is initiated (Johnsson et al., 1996).

The quality of growth in the three cichlid species in aquaculture establishments was of a higher quality than that found in nature (Metcalfe et al., 1988), which was disturbed by factors such as lipid or weight levels and the pace of adjustments in growing proportions at the time (Thorpe, 1986). Such fast development degrees are inherited in the aquaculture samples (Thorpe, 1986). The current findings displayed that the aquaculture groups of the three cichlid species examined disclosed discrepancies in health apart from those of the feral group that originated from taming and were associated with planned and not deliberate choice. As greatly of this variation figured to be an adaptable reaction to the aquaculture setting, it can be of importance for plans endeavoring to develop aquaculture invention (Doyle et al., 1991). However, this dissimilarity poses a threat to wild communities when fish escape and compete with and breed with three wild cichlid species. There is increased competition for resources and the introduction of new genetic traits into feral populations when samples from aquaculture flow off into rivers. Due to the non-native origins of the aquaculture group and the variations that have emerged over farming, numerous of these characteristics are thought to be harmful to local ecosystems (Einum & Fleming, 1997). Although natural selection has the potential to rid wild populations of these superfluous traits, the annual influx of aquaculture populations makes this process very difficult, if not impossible.

The present finding that distinguishes between aquaculture and feral populations of the three cichlid species focused on the external and meristic features shown by the results of Barriga-Sosa et al. (2004) and Narváez et al. (2005), who stated the morphological discrepancies amid feral and aquaculture groups of Nile tilapia (O. niloticus). Researchers have classified such distinctions into the categories of food, environment, and surroundings (feral and farmed). However, in the current investigation, all meristic characteristics were significantly unlike between the groups studied, which disagrees with the study conducted by Solomon et al. (2015) on Clarias gariepinus.

Compared to other vertebrates, fishes often exhibit more variety in morphological traits within and between species as well as across groups. According to Allendorf (1988), Thompson (1991), and Wimberger (1992), the change signifies a shift in feed areas, predator types, accessibility to food, and additional environmental issues.

The morphological and meristic evaluations of aquaculture and feral groups of three cichlid species investigated in this study disclose substantial phenotypical deviations induced by habitat settings. Aquaculture groups frequently demonstrated differing attributes, like modified body outlines, such as deeper bodies and shorter caudal peduncles, with meristic modifications like fin ray or scale count disparities, accountable to breeding methods, such as regulated alimentation, decreased preying on, and expanse restraints. Conversely, feral groups demonstrated morphology adjusted for ecological niches, highlighting attributes correlated to the ability to search for food, hunter avoidance, and hydrodynamic capability. Such naturally evoked lack of correspondence emphasizes the part that phenotypical flexibility plays in cichlids, proposing that external feature disparity only may not suggest taxonomical differences. These conclusions warn against dependence on conventional morpho-taxonomic techniques, as conflicting attributes in regulated habitats might hide actual developmental links or mock species dispersal.

The perceived dissimilarities between reared and feral cichlid groups give emphasis to serious encounters for cichlid classification. In case the morphological attributes deviation is taken the wrong way as a genetic distinction, systemists imperil incorrectly dividing groups that live in the same habitat into dissimilar taxa or concealing valid species borders. As an example, flexibility in meristic attributes such as NDFR could precede to expanded species accounts, while body measurements merging in aquaculture might obscure differences between species. Highlights the need to combine hereditary, habitat, and biogeographical information with conventional morphological methods to delimit species correctly. Likewise, such outcomes recommend a re-inspection of historic categorizations, specifically for cichlids with prevalent breeding instigations, where non-natural collection and habitat impacts could pose difficulties for taxonomic precision. Finally, these visions are a support for adaptable classification contexts that credit phenotypical flexibility, guaranteeing vigorous species control and protection approaches in both natural and man-made changed habitats.

Data for C. zillii, O. aureus, and O. niloticus from the wild and from the aquaculture facility after 2018–2019 sampling period were unavailable due to exceptionally low wild population density at the sampling site. Consequently, the analysis focuses on the datasets where robust paired comparisons between wild and farmed stocks were feasible. While this study utilized data from 2018 to 2019, its findings remain highly relevant. The results establish a crucial baseline for the morphological characteristics of key cichlid species in central Iraq prior to the accelerated environmental changes observed in recent years. The demonstrated efficacy of morphometric and meristic analysis for discriminating between wild and farmed stocks provides a cost-effective tool for ongoing monitoring programs. This is essential for managing potential ecological interactions, such as interbreeding or competition, between escaped aquaculture fish and native wild populations. Future studies building upon this baseline will be critical for assessing the long-term impacts of aquaculture and climate change on Iraq’s aquatic biodiversity.

Further investigations on the operational meaning of the morphological distinctions attained in the existing examination on the three cichlid fish species might aid in explaining the influence of morphological discrepancy on the endurance of aquaculture samples in the wild. To conduct more comprehensive assessments of the impact of escaped fish samples from an aquaculture facility on feral fish groups or fishery landings or to evaluate supplying plans, collaborative methodology such as genetic, morphometric, and other biological markers (e.g., size and otolith growth patterns, fatty acids, and trace elements) will be used. This will help with the creation of plans for the long-term preservation and sustainability of natural stock and will also significantly enhance our knowledge of the species’ biology and ecology.