First data on the freshwater fish fauna of Calabria (southern Italy)

Abstract

There is scarce information available about the presence and distribution of freshwater fishes in southern Italy, and ichthyological information about Calabrian lotic systems is practically inexistent. This paper reports the current status of the freshwater fish fauna in some of the most important lotic systems of Calabria. Ichthyological samplings were performed at 54 stations along 16 Calabrian rivers. Sixteen fish species belonging to eight families were found, and their presence and distribution is discussed on the basis of biogeographic considerations. The freshwater fish fauna of the area has been dramatically altered by the introduction of allochthonous species, mainly originating from the Po plain catchments. This is a prime example of faunistic transformation of a Mediterranean area.

Keywords:

• Freshwater fishes
• Calabria
• ichthyology
• allochthonous species

Introduction

The natural distribution of the native fish fauna in Italy is the result of complex palaeogeographic and palaeoecological processes. Bianco (1995) recognized four categories of freshwater fishes in Italy based on salinity tolerance: 1) Primary, taxa that originated and spread only in freshwaters (such as Cypriniformes); 2) Primary-like, freshwater species of marine origin (such as many Gobiidae); 3) Secondary, euryhaline taxa that can survive in marine environments (such as Cyprinodontidae); 4) Peripheral, recent marine derivates and diadromous taxa (such as Salmonidae, Gasterosteidae and Acipenseridae). The dispersal capacity differs among these groups. Primary freshwater fishes are an important group for biogeographic studies since they tolerate only low salt concentrations and are unable to disperse through marine environments. Hence, unlike secondary and peripheral fishes, they cannot spread from one river network to another via the sea and their distribution is strictly related to the history of hydrographical systems.

On the basis of the distribution of indigenous taxa, Bianco (1990) identified two distinct ichthyogeographic regions in the Italian peninsula, with many endemisms possibly isolated since the Messinian Age (about 5 million years ago). The Padano-Venetian district contains basins of the middle and upper Adriatic Sea north of the Vomano River, while the Tuscano-Latium district includes the Serchio, Arno, Ombrone and Tiber basins. For palaeogeographic reasons, southern Italian basins were isolated from the rest of the peninsula and contain few or no native primary freshwater fishes; rivers and streams of this area were colonised mainly by saline-tolerant species coming from the Mediterranean.

There have been few studies on the presence and distribution of freshwater fishes in southern Italy, and ichthyological information regarding Calabrian lotic systems is practically inexistent. A few non-primary species (such as Anguilla anguilla Linnaeus 1758, Salaria fluviatilis (Asso 1801) and Salmo (trutta) macrostigma Duméril 1858) are represented; according to Rogliano (1963) and Bianco (1981, 1987), they are the only native freshwater fishes present in most of Calabria (e.g., in the running waters of the Sila mountain system), where many streams are naturally devoid of fish fauna. The only available information comes from occasional and isolated reports on the presence of single species in particular Calabrian rivers (e.g., Rogliano 1963; Bianco 1981, 1987). The aim of the present study is to provide the first information on the current distribution of fish species in some Calabrian catchments.

Materials and methods

This study collates data from some ichthyological surveys in Calabria (southern Italy). Fifty-four sites along 16 rivers were analysed to investigate the presence and distribution of fishes (Figure 1). The rivers (and stations) were: Abatemarco (AB1-AB2), Coscile (CO1-CO5), Crati (C1-C5), Esaro (ES1-ES3), Lao (L1-L3), Lipuda (LI1-LI2), Neto (NE1-NE5), Ampollino (AM1), Lese (LE1-LE2), Vitravo (VI1-VI3), Rosa (RS1-RS2), Savuto (SV1-SV4), Tacina (TA1-TA7), San Antonio (SAN1-SAN2), Soleo (SO1-SO3), and Trionto (TR1-TR4). The location of each sampling station within a river reach was selected in the field based on representativeness and accessibility: various habitat types (pools, riffles and runs) were sampled on each occasion. During low flow conditions, we electrofished each station by passing once upstream, searching from one bank to the other following the methods outlined by Bohlin et al. (1989), for a total length of almost 200 m. Single-pass qualitative electrofishing was conducted using a backpack electric fishing machine (SCUBLA ELT60, operated at 25--100 Hz and 300/550 V, depending on the water conductivity). Single-pass electrofishing is a suitable and common method for assessing the distribution of freshwater fishes in small and medium-sized lotic environments (Jowett & Richardson 1996; CEN 2003; Maceda-Veiga et al. 2010). Fish were identified at species level based on Kottelat and Freyhof (2007), then were released. Cluster analysis using the Bray-Curtis similarity coefficient (single linkage — Bray & Curtis 1957) was applied to identify the faunal similarity of stations, and a similarity dendrogram was produced using Biodiversity Pro software (McAleece et al. 1997).

Figure 1. Main Calabrian lotic systems and sampling stations.

Results

The following is a list of native and introduced fish species recorded at the 54 study sites.

Autochthonous taxa

none	Anguilla anguilla (Linnaeus, 1758) (Anguillidae)
none	Salaria fluviatilis (Asso, 1801) (Blennidae)
none	Liza ramada (Risso, 1826) (Mugilidae)

Allochthonous taxa

none	Rutilus rubilio (Bonaparte, 1837) (Cyprinidae)
none	Alburnus alburnus alborella (De Filippi, 1844) (Cyprinidae)
none	Barbus plebejus (Bonaparte, 1839) (Cyprinidae)
none	Squalius cephalus (Linnaeus, 1758) (Cyprinidae)
none	Scardinius erythrophthalmus (Linnaeus, 1758) (Cyprinidae)
none	Carassius carassius (Linnaeus, 1758) (Cyprinidae)
none	Cyprinus carpio (Linnaeus, 1758) (Cyprinidae)
none	Tinca tinca (Linnaeus, 1758) (Cyprinidae)
none	Cobitis taenia (Linnaeus, 1758) (Cobitidae)
none	Salmo (trutta) trutta (Linnaeus, 1758) (Salmonidae)
none	Onchorynchus mykiss (Walbaum, 1792) (Salmonidae)
none	Ameiurus melas (Rafinesque, 1820) (Ictaluridae)
none	Gambusia holbrooki (Girare, 1859) (Poeciliidae)

The dates of introduction of the allochthonous species are not known, with a single exception. Fish introductions have been carried out in an uncoordinated, sporadic and illegal manner. Local fishermen's associations and single individuals have introduced several alien species, obviously without leaving a trace in documents or publications. The introduction date is known only for G. holbrooki: this poecilid was first introduced into Calabria in 1928--31 as part of a large anti-mosquito campaign (Paladino-Blandini 1933). The distributions of fish species are reported in Table I.

Table I. List of freshwater fish species collected at the sampling stations

	Salmo (t.) trutta	Squalius cephalus	Barbus plebejus	Carassius carassius	Anguilla anguilla	Ameiurus melas	Liza ramada	Rutilus rubilio	Cyprinus carpio	Al burnus (a.) alborella	Salaria fluviatilis	Scardinius erythrophthalmus	Cobitis taenia	Gambusia holbrooki	Onchorynchus mykiss	Tinca tinca
AB1	X
AB2	X				X
C1	X
C2	X	X
C3		X						X	X
C4		X						X	X	X
C5		X	X			X		X	X	X
C6			X	X			X	X	X
C7		X	X	X	X	X	X	X
Co1	X				X
Co2	X
Co3	X	X	X		X
Co4		X	X	X	X		X	X	X
Co5		X	X	X	X		X	X	X
Es1	X	X						X		X	X
Es2		X	X	X				X	X	X
Es3		X	X		X		X	X		X
L1	X				X					X
L2	X				X
L3		X			X			X		X	X
NE2	X	X			X			X		X	X			X
NE3		X						X	X	X
NE4		X					X		X	X	X			X
NE5		X			X		X		X	X	X
LE1	X
LE2										X			X	X
VI1	X
VI2		X						X	X				X
VI3		X		X					X				X
Rs1	X
Rs2	X
Sv1	X											X
Sv2	X
Sv3		X						X					X
Sv4		X						X					X
TA2	X											X			X
TA4		X		X				X					X			X
TA5								X		X			X			X
TA6					X			X	X	X	X
TA7		X			X				X	X	X			X
SAN1	X														X
SAN2					X			X		X	X		X
SO1	X
SO2	X				X
T1	X
T4								X

Nine of the stations were fishless, eleven stations had only one species and only four presented a relatively rich fish community, with a total of seven species. The Bray-Curtis similarity analysis showed two distinct major clusters (Figure 2).

Figure 2. Bray-Curtis similarity dendrogram regarding 54 freshwater fish sampling stations.

Discussion and conclusions

This study is the first structured attempt to analyse the presence and distribution of freshwater fishes in major lotic systems of Calabria. The analysis of data from 16 rivers, from both the Ionian and Tyrrhenian sides of the region, produced a preliminary but quite comprehensive picture of the current situation.

Headwaters of Abatemarco, Coscile, Crati, Lese, Rosa, San Antonio, Savuto, Soleo, Trionto and Vitravo contained stations with Salmo (trutta) trutta: trout were found as the only fish taxon, or in association with A. anguilla, or more rarely with O. mykiss or some accompanying cyprinids, mainly S. cephalus and B. plebejus. The other most important cluster is characterized by stations lacking Salmonidae, with various assemblages of Cyprinidae (for the most part including L. cephalus, R. rubilio, C. carpio) and other species. Two minor clusters can be recognized within this group: a first cluster (including mainly lowland stations of the Neto hydrographical network plus the final segment of Tacina) is characterized by A. anguilla, S. fluviatilis and G. holbrooki, while the other (including stations from the Crati network plus a few others from the Neto and Tacina networks) is characterized by B. plebejus, C. carassius and L. ramada. The final part of the Trionto River is isolated in the cluster analysis: this station corresponds to a peculiar environment called ‘fiumara’. The presence of R. rubilio at this station is limited to a few deep pools and can be considered occasional and ephemeral. The middle part of the Lese also constituted a separate group in the cluster analysis, since only small allochthonous fishes (A. alburnus, C. taenia, G. holbrooki) were present at this station.

Bianco (1987) reported that the cyprinid distribution in southern Italy was limited to rivers north of the line connecting Sinni (Basilicata) and Alento (Campania), while other studies (Rogliano 1963; Bianco 1980) reported that Calabrian catchments did not naturally contain primary species or even had no fishes. We report, for the first time, that this original situation has dramatically changed because of the massive introduction of allochthonous species, mostly originating from Po plain catchments (such as L. cephalus, B. plebejus, R. rubilio, S. erythrophtalmus and C. taenia). Nine stations were fishless, probably for historical reasons because there is no evidence of high alteration or pollution levels. Headwaters often hosted a fish community dominated by trout, alone or in association with eels: this could be the typical fish assemblage of the area, although the trout often clearly belonged to the Atlantic strain and thus derived from anthropogenic introductions. Lowland lotic environments were dominated by alien fish species, probably because most introduced fish species are limnophilic, preferring waters with slow current. In this context, southern catchments were to some extent separated in the cluster analysis from the Crati catchment: this difference in fish fauna composition can most likely be related to different episodes of introductions and to some environmental differences among stations (mainly regarding streambed width, water column depth, conductivity).

The present distribution of freshwater fishes in Calabria is the result of recent events, mostly related to human interventions. In fact, introductions have radically altered the original distributions of freshwater fishes in almost all Italian basins (Gandolfi et al. 1991; Zerunian 2002). The displacement of fishes into new hydrographical basins has been a common practice for a long time: Romans were the first to breed and introduce carps (Cyprinus carpio) from the Danube to the Mediterranean area for breeding purposes, and the tradition of “piscinae” was extensive in monasteries throughout Europe in the Middle Ages (Balon 1995). Another interesting example of fish introduction is the rainbow trout (Onchorynchus mykiss): this species has been released in almost all continents (except Antarctica) for recreational fishing, with a great impact on the local fauna (Cambray 2003). However, while the introduction of a single species can represent a serious but also localised threat to biodiversity, a totally different scenario is represented by the complete change of the fish fauna of an entire area, as has occurred in Calabria. The original Calabrian situation has dramatically changed because of the massive introduction of allochthonous species, mostly originating from Po plain catchments. The official and unofficial introduction of “white fishes” has caused a process of ‘padanization’ (sensu Cambray 2003) in most basins of Calabria. Fish introductions reflect human interest, suitable environmental conditions for fish establishment and the biological attributes of the introduced fish species. Some species were introduced for direct (such as S. trutta, O. mykiss, C. carpio, I. melas and many Cyprinidae) or indirect fishing purposes (such as C. taenia, probably introduced into Lake Ampollino and the Savuto river as food for introduced trout, as suggested by Bianco & Taraborelli 1984). As mentioned previously, G. holbrooki was introduced for mosquito control (Paladino-Blandini 1933). The high tolerance level of some introduced species (such as S. cephalus) surely played an important role in their widespread diffusion. Human introductions altered biodiversity at the community level, but also altered genetic pools at the population level: in particular, allochthonous brown trout strains dramatically altered the genetic characteristics of native populations. As reported by Nonnis Marzano et al. (2003), domesticated strains of S. (trutta) trutta (also known as morpha fario) were transferred from northern Italy to most of the southern freshwater basins during the last century without consideration of the presence of native populations of S. (trutta) macrostigma. This practice was subsequently replaced by the introduction of brown trout of Atlantic origin. In fact, our findings confirm for Calabria the hypothesis of Schöffmann et al. (2007) that most recently introduced trout have come from hatchery stocks of Atlantic origin (Ketmaier & Bianco 2004) whereas in the past century many southern Italian rivers were stocked with hatchery-reared brown trout originating from the northern part of the Mediterranean basin (Sommani 1969). A very puzzling situation was found during our samplings: some specimens from a few populations (found for example in the upper Lese, San Antonio and Lao) had phenotypic characters that could be referred to the macrostigma type, such as the permanence of parr marks in the adults. Unfortunately, most populations were clearly derived by recent or contemporary introductions, with trout mainly having Atlantic phenotypic traits.

In a recent study, Leprieur et al. (2008) included south-western Europe among the six most important global invasion hotspots, where non-native species represent more than a quarter of the total number of species per basin. However, information about southern Italy and especially Calabria has always been lacking. Our study fills this gap, showing that this area is an important invasion hotspot, with introduced fish species representing 68% of the total fish species richness. This is a very high percentage, compared to the percentages of non-native species reported in other Mediterranean regions such as most of Spain (5--20%) and Greece (0--5%, Leprieur et al. 2008). Interestingly, while northern and central Italian basins have undergone a diffuse ‘danubianization’ and ‘globalisation’ of their ichthyological communities (Maio 2002), the Calabrian fish fauna has been altered by the massive introduction of Padano-Venetian species.

Some factors may have favoured the establishment of alien species, such as the absence of native competitors and the high plasticity and environmental tolerance of introduced taxa. In the present situation, it may be difficult to make proposals concerning the conservation and recovery of native fish assemblages. However, reducing habitat fragmentation by the removal of small and large physical obstacles or the realization of fish passages could improve the distribution of A. anguilla. Dams and small weirs are probably the main reason for the absence of migratory species such as the European eel in many headwaters; furthermore, dams can be a source of alien species for downstream reaches (as for S. erythrophthalmus in the Savuto River). Furthermore, releases of any non-native species should be prohibited. Finally, genetic studies of trout seem to be indispensable to select native strains for the production of eggs and fry to be used in restocking programs.