The occurrence, distribution and biology of invasive fish species in fresh and brackish water bodies of NE Morocco

Study Extent

Morocco is currently divided into 12 administrative regions, including the Oriental Region (fig. 1), which occupies almost all the eastern side of the country and covers an area of 88,681 km2 (see Mabrouki et al., 2018 for details). The Oriental Region includes the wilaya of Oujda (Oujda–Angad prefecture) and the provinces of Berkane, Driouch, Figuig, Guercif, Jerada, Nador and Taourirt. The watershed of the Moulouya (fig. 1), which includes nearly 43,412 km2 of eastern Morocco, covers much of the Oriental Region. With a length of 600 km, the Moulouya is the longest Moroccan River flowing into the Mediterranean. Its main tributaries are the Oueds Ansegmir, Melloulou, Za and Msoun, all permanent. Other tributaries are presently intermittent (3–5 flash floods on average per year) (Bensaad et al., 2017; Mabrouki et al., 2017).

Sampling

Field investigations (often in the framework of various hydrobiological studies) have been carried out since 2014 at 45 stations throughout the Moulouya River basin, including its main affluents: Oued Anzegmir (side of the High Atlas), Oued Melloulou (Middle Atlas slope) and Oued Za (High Plateau), and at about 60 stations spread throughout eastern Morocco from the northern regions of Nador and Saïdia, to Figuig in the southeast and Talessint and Bouanane in the southwest (fig.1). The stations that showed the occurrence of the mentioned fish species were re-examined between 2017 and 2018. Quantitative sampling of fish fauna was carried out using nets, searching in the most suitable places for the studied species. Sampling lasted an average of one hour over an area of 10 m2 at each station, sufficient time to trap and catch virtually all the fish in each area. Invasive species caught were preserved in formalin solution, while native fish (especially fry) were returned to the water. Permission to perform these studied was granted by the authorities.

Quality Control

Statistical analyses were carried out using software R package version 3.3.1. (R Core Team, 2019). In the modelling of counting processes, here the abundance of a species, two kinds of models are commonly implemented, namely the Poisson model and the negative binomial model (Hilbe, 2011). Frequently, counting data is characterized by overdispersion, whereby the sample variance is greater than its average. In the case where the anomalous dispersion is proved, the Poisson regression is no longer suitable for modelling this distribution, and the negative binomial regression model, allowing more flexibility in the dispersion, should be used. The relevance of Poisson regression or negative binomial models was evaluated by the Pearson Residue Test (Plackett, 1983).

Method steps

1. For this study, ten environmental parameters were selected: sulfate (SO42–), biological oxygen demand after 5 days (BOD5), phosphate (PO43–) and nitrate (N-NO3) were measured in the laboratory. Conductivity, salinity, pH, dissolved oxygen, temperature and the mean depth were measured in situ using a multiparametric measuring device (WTW, Multi-Line P4). Two replicas of water samples from each station were taken in 500 ml polyethylene bottles. The water samples were preserved with 2 ml of concentrated hydrochloric acid (pH = 2). According to standards ISO 5667-6 (1990), ISO 5667-2 (1991) and ISO 5667-3 (1994), water samples were transported in a cooler at a low temperature (± 4 °C) to stop the metabolic activities of organisms in the water. The current velocity, well known for its selective action on habitat and species distribution (Mabrouki et al., 2019a), was quantified by its mean value at three different locations of the same station. In the absence of a hydrometric reel to measure current velocity it was estimated using a stopwatch at various points of the watercourse by measuring the time it takes for a floating object to cross a given path. The average speed (converted to cm–1) was semi-quantitatively estimated, followed by a transformation into three modalities: 1, very low to no current < 5 cm–1; 2, low current 5 < 2 < 25 cm–1; and 3, average current 25 < 3 < 50 cm-1.

1. Aphanidae
   rank: family
2. Aphanius fasciatus
   rank: species
3. Fundulidae
   rank: family
4. Fundulus heteroclitus
   rank: species
5. Poeciliidae
   rank: family
6. Gambusia holbrooki
   rank: species

Morocco is currently divided into 12 administrative regions, including the Oriental Region (fig. 1), which occupies almost all the eastern side of the country and covers an area of 88,681 km2 (see Mabrouki et al., 2018 for details). The Oriental Region includes the wilaya of Oujda (Oujda–Angad prefecture) and the provinces of Berkane, Driouch, Figuig, Guercif, Jerada, Nador and Taourirt. The watershed of the Moulouya (fig. 1), which includes nearly 43,412 km2 of eastern Morocco, covers much of the Oriental Region. With a length of 600 km, the Moulouya is the longest Moroccan River flowing into the Mediterranean. Its main tributaries are the Oueds Ansegmir, Melloulou, Za and Msoun, all permanent. Other tributaries are presently intermittent (3–5 flash floods on average per year) (Bensaad et al., 2017; Mabrouki et al., 2017). Surveys Field investigations (often in the framework of various hydrobiological studies) have been carried out since 2014 at 45 stations throughout the Moulouya River basin, including its main affluents: Oued Anzegmir (side of the High Atlas), Oued Melloulou (Middle Atlas slope) and Oued Za (High Plateau), and at about 60 stations spread throughout eastern Morocco from the northern regions of Nador and Saïdia, to Figuig in the southeast and Talessint and Bouanane in the southwest (fig.1). The stations that showed the occurrence of the mentioned fish species were re-examined between 2017 and 2018. Quantitative sampling of fish fauna was carried out using nets, searching in the most suitable places for the studied species. Sampling lasted an average of one hour over an area of 10 m2 at each station, sufficient time to trap and catch virtually all the fish in each area. Invasive species caught were preserved in formalin solution, while native fish (especially fry) were returned to the water. Permission to perform these studied was granted by the authorities.