Oreochromis mossambicus, (Peters, 1852) (Peters, 1852)

Lasso-Alcalá, Oscar M., Bello Pulido, Jesús A., Quintero-T., Elena, Mikolji, Ivan D. & Peñuela, José H., 2023, The Mozambique Tilapia (Oreochromis mossambicus), in hypersaline waters of Venezuela, Southeastern Caribbean Sea, Anartia (Oxford, England) 36, pp. 51-62 : 54-57

RESULTS AND DISCUSSION

On November 21, 2017, a total of 17 specimens (between 180 and 230 mm SL) of Oreochromis mossambicus were captured, in an internal sector of the Laguna de Chacopata , between the 10°39’28.55” N - 63°49’09.40” W ( Fig. 1B). Likewise, other specimens from the Laguna de Bocaripo were observed but not examined, because they were used by other fishermen for consumption. These specimens were only measured and not preserved ( Fig. 2). Additionally, on March 15, 2023, about 19 specimens were captured, preserved and transferred to the MHNLS. A summary of the basic meristic and morphometric data of the examined specimens is presented in Table 1 .

The examined specimens presented the morphological and chromatic diagnostic characters of the species ( Trewavas 1982, 1983; Skelton 1993, Lamboj 2004): Long head and snout, with two to three scales in the interocular region and 9 to 12 scales in the nuchal region, up to the origin of the dorsal fin. Dorsal with 15-18 spines and 10-13 rays. Anal fin with 3 spines and 7 to 12 rays, 14 to 20 gill rakers on its lower arm. Fine teeth closely knit in several rows on both jaws. External ones in unicuspid or caninoid mature males. Caudal fin abundantly scaled in the initial two-thirds of its surface, with the final third free of scales. In females and juveniles, the color of the body is light gray, with cream on the ventral region, presence of two to five spots along the middle region, yellow iris, and dark gray fins. Males present a characteristic sexual dimorphism expressed by the elongation of the lower jaw, which gives it a concave profile in the upper part of the muzzle. This modification is developed to attend reproductive activities, such as the excavation of nests at the bottom of the substrate. Likewise, the coloration is from a very dark gray to black throughout the body, including fins and irises, cheeks with yellowish tones, with red edges of the dorsal and tail fins, as well as the pectorals, in hyaline red tone ( Fig. 2).

Oreochromis mossambicus is a species of the Cichlidae family, native to seven countries of the Southeast Africa, including the middle and lower basins of the Zambezi, Shire, Brak, Bushmans, Kwazulu-Natal and Limpopo rivers, coastal plains from the Zambezi Delta to Algoa Bay, in Mozambique, Malawi, Botswana, Zimbabwe, Eswatini, Lesotho, and South Africa ( Philippart & Ruwet 1982, Trewavas 1982, 1983; Pullin 1988, Skelton 1993, Lamboj 2004, Firmat et al. 2013). For mainly aquaculture purposes, this species has been introduced in around 104 nations; of these, in at least 94 countries in the world (13 in Africa, one in Europe, 26 in Asia, 23 in Oceania and 31 in America [including Venezuela]), it has been successfully established ( Welcomme 1988, Canonico et al. 2005, Froese & Pauly 2023).

In Venezuela, this species was introduced from Trinidad Island (formally Republic of Trinidad and Tobago) in 1958, for the purpose of experimental aquaculture in the Estación de Piscicultura , Ministerio de Agricultura y Cría , located at El Limón , Maracay (endorheic basin of Lago de Valencia , central region of Venezuela), as indicated by some studies ( Luengo 1963, 1970; Ramírez 1971, Welcomme 1988, Lasso-Alcalá 2001, 2003). From there, in 1964, 800 specimens were introduced into the coastal system adjacent to the mouth of the Río Manzanares , known as Laguna de Los Patos (coast of the city of Cumaná , eastern region of Venezuela: Fig. 1A); with the aim of experimental aquaculture by the Universidad de Oriente ( Kahndker 1964, Carvajal 1965, Luengo 1970). Twelve years after this introduction, the disappearance of 75% of the fish and crustacean species previously known for said littoral ecosystem is noted ( Aguilera & Carvajal 1976, Jiménez 1977). Subsequently , from the Laguna de Los Patos , where it still lives today, this species quickly dispersed and invaded the coasts of the Caribbean Sea in the Golfo de Cariaco ( Nirchio & Pérez 2002, Gaspar 2008) and the Laguna de Punta Delgada ( Marín et al. 2003) ( Fig. 1A), thanks to its known broad tolerance to salinity ( Philippart & Ruwet 1982, Trewavas 1982, Pullin 1988). In the Río Manzanares basin, it has invaded from its mouth or estuary to the middle system ( Aricagua River , 250 m asl, pers. obs.), as well as the rainwater and wastewater collection systems of the city of Cumaná ( Fig. 1A) ( Nirchio & Pérez 2002. Pérez et al. 2003, Senior et al. 2004, Ruíz et al. 2005, Pérez et al. 2006b). Likewise, it has also been registered as introduced into the Río Barbacoas and its mouth ( Chung 1990), as well as the Laguna de Campoma and mouth of Campoma river ( Bonilla et al. 2010; pers. obs.), belonging to the Campoma and Casanay rivers basin, which empties in the eastern end or Saco at Golfo de Cariaco ( Fig. 1). Additionally and recently, it has also been recorded in Laguna de Los Mártires, in the northwest coast of Isla de Margarita ( Rodríguez et al. 2021; Fig. 1C). In this coastal lagoon, a generalized loss of biodiversity was found, due to the displacement and extinction of native species, where the disappearance of at least 85% of the fish community is estimated, as well as changes in the specific composition and the native community structure; and the dramatic reduction of the abundance, biomass and frequency of the native species.

In the hypersaline lagoon system of Chacopata and Bocaripo ( Fig. 1B), the fishes constitute one of the relatively best documented groups, with five studies on their biodiversity, community structure and predation, which from 1983 to 2018 quantified about 47 native species of marine and estuarine habits ( Oliveros & Martínez 1984, Acosta1985, Meaño1986, Valecillos 1993, Pérez et al. 2012, Rojas et al. 2018). Likewise, according to the local fishermen, the discovery of Oreochromis mossambicus during their fishing operations in this lagoon system dates from at least 2011. This coincides with our investigations, since in the samplings carried out between 2007 and 2008, this species was not recorded ( Pérez et al. 2012). Although it is not fully certain, we believe that its introduction into this ecosystem has been intentional, due to its proximity to other systems where the species has already been introduced. Those nearby systems are the Laguna de Campoma and Campoma river mouth (27 km away), where it has been established since at least 2009, the Laguna de Punta Delgada (38 km away), since at least 2000 (Elizabeth Méndez, pers. com.) and Laguna de Los Patos (48 km away) since 1964, as stated at the beginning of this work (see Figs. 1A, B). In addition to the short distance between these ecosystems, another argument that supports this hypothesis of intentional introduction is the importance of this species for subsistence fishing of other communities of artisanal fishermen, such as those located on the coast of Cumaná and some coastal area communities of the Golfo de Cariaco. In those fishing communities, O. mossambicus is appreciated as a subsistence food and locally known by the common name of “ universitario ”, since its origin in the region is recognized and attributed to the Universidad de Oriente.

Due to its tolerance of large variations in environmental parameters (e.g.: temperature, salinity, dissolved oxygen, pH, etc.), the Mozambique Tilapia has successfully colonized and invaded freshwater lakes, rivers, swamps, estuaries, coastal brackish lagoons, coral atolls, hypersaline desert lakes and hot springs where it has been introduced throughout the world (Trewavas 1983). Some authors indicate that it is a common species in closed estuaries and coastal lagoons ( Blaber 1997), but generally absent in permanently open estuaries and open seas ( de Moor & Bruton 1988). Contrary to this, in Venezuela, it has been recorded in the mouths of rivers such as the Manzanares and Barbacoas, and open lagoons such as Los Patos, and Punta Delgada, as well as in the adjacent sea in the Golfo de Cariaco ( Chung 1990, Nirchio & Pérez 2002, Marín et al. 2003, Gaspar 2008; Fig. 1A), Laguna de Los Mártires ( Isla de Margarita: Rodríguez et al. 2021; Fig. 1C) and in the present work we recorded it in the open coastal lagoons of Chacopata and Bocaripo ( Fig. 1B).

Also, Oreochromis mossambicus has been successfully introduced and established in other marine ecosystems. In the Greater Caribbean region ( Caribbean Sea and Gulf of Mexico), just to name a some cases, this species is found introduced in coastal marine lagoons, river estuaries, internal salt ponds, and open bays on islands and coastal waters, for example the USA ( Baker et al. 2004), México ( Raz-Guzmán et al. 2018), Puerto Rico ( Burger et al. 1992), Aruba, Curaçao and Bonaire islands ( Debrot 2003; Hulsman et al. 2008), Trinidad Island ( Joseph et al. 2022) and Tobago Island ( Mohammed 2014), in salinities ranging from 5 to 39 PSU. In the Southeastern Caribbean Sea (Northeastern region of Venezuela), salinities between 0 and 38 PSU have been recorded at the mouths of the Manzanares and Barbacoas rivers, Laguna de Los Patos, Laguna de Punta Delgada, Laguna de Campoma, the Golfo de Cariaco ( Fig. 1A) and Laguna de Los Mártires ( Fig. 1C) (Carbajal 1972, Chung 1990, Nirchio & Pérez 2002, Marín et al. 2003, Gaspar 2008, Rodríguez et al. 2021). This corresponds in part to the hypersaline conditions (> 40 PSU) in which we found O. mossambicus in the negative estuary of Chacopata and Bocaripo, whose registered salinity values range from 32.00 to 70.67 PSU (Todelo et al. 2000, Prieto et al. 2009, Pérez et al. 2012, Jiménez-Ramos et al. 2019); the latter is one of the highest values recorded for this species in a natural ecosystem. This salinity is even higher than other hypersaline ecosystems (internal lakes) where this species has been introduced; such as the Salton Sea (lake), in California ( USA), where maximum salinity is 44 PSU ( Caskey et al. 2007). However, in its natural range, for example in Saint Lucia Lake, an originally open estuary in South Africa, Whitfield and Blaber (1979) indicated that O. mossambicus can tolerate gradual changes in salinity to 120 PSU. According to these authors, ecologically, owing to its freshwater origin, Oreochromis mossambicus has been classified as a highly Euryhaline species (tolerance of 0 to 36 PSU). It is very likely that its extraordinary adaptive plasticity to new marine and hypersaline ecosystems, although with certain limitations in some locations, is due to genetic characteristics such as epigenetic modifications or adaptive mutations ( Pérez et al. 2006b).

It is important to state that the introduction, establishment and invasion of Oreochromis mossambicus has a series of implications and consequences, given other biological and ecological characteristics of this species of cichlid. Among these are its omnivorous and piscivorous predatory habits, moderate fecundity but with strong parental care of eggs and young (territorialism), and rapid population growth. Therefore, the ecological consequences from the introduced fish of this family are unpredictable ( Lasso-Alcalá et al. 2014). Some of the consequences that have been observed with the native fauna of the 94 countries where O. mossambicus has been introduced and is established, are: The direct predation of eggs, larvae, juveniles and adults; interspecific competition; reduction of abundance and biomass; displacement and extinction of species; changes in the specific composition and trophic structure of communities; generalized loss of biodiversity in the ecosystem; destruction and alteration of habitat; hybridization with species of the same or relative genus (only in Africa); and transfer of parasites ( Aguilera & Carvajal 1976, Jiménez 1977, Canonico et al. 2005, Gutiérrez et al. 2012,Firmat etal.2013,Cassemiro etal.2018, Wilson 2019, Rodríguez et al. 2021). For these reasons, O. mossambicus has been listed as one of the 100 most harmful invasive alien species in the world ( Lowe et al. 2004).

Taking into account this panorama and the current knowledge about the fish diversity of the study area in this work, it is necessary to carry out a monitoring program of the lagoon system of Chacopata and Bocaripo to determine if this invasive species has caused a change in the taxonomic and/or structural composition of the community of fish and other organisms of this ecosystem. Likewise, the presence of this and other species introduced in different coastal lagoon systems of Venezuela where they have not been detected must be evaluated, since most of the studies ( Weibezahn 1949, Mago 1965, Fernández-Yépez 1970, Gómez 1981, Heredia 1983, Cervigón & Gómez 1986, Jory 1988, Rodenas & López-Rojas 1993, Ramírez-Villarroel 1993, 1994a, b, López-Rojas et al 1996, Marín 2000; Andrés de Grado & Bashirullah 2001, Barreto et al. 2009), have been carried out more than 10 years ago. It is evident that the situation in these ecosystems must have changed. This situation is particularly disturbing if other antecedents are taken into account, since on the coasts of Venezuela, at least six other species of estuarine and marine fish ( Eleotris picta , Omobranchus sewalli , Butis koilomatodon , Gobiosoma bosc , Pterois volitans and Neopomacentrus cyanomos ) have been identified as introduced, some of them being strongly invasive ( Pezold & Cage 2002, Lasso et al 2004, Lasso-Alcalá et al. 2005a, b, 2008, Lasso-Alcalá & Posada 2010, Lasso-Alcalá et al. 2011, 2019; Cabezas et al. 2020, 2022). Added to this is the recent invasion of the octocoral Unomia stolonifera ( Alcyonacea , Xeniidae ), native to the Pacific Ocean, which is seriously impacting the native species and coastal marine ecosystems of Venezuela (Ruiz-Allais et al. 2022), and is already beginning to disperse throughout the Greater Caribbean ( Espinosa et al. 2023) .