Distinction of the Gambusia species introduced in Italy

Stefano Valdesalici * & Diego Montanari**

* Via Cà Bertacchi N.5, 42030 Viano (RE), Italy. Email: valdekil@tin.it

Abstract

Italy was one of the first country where Gambusia species was introduced as mosquito control agent at the start of last century. This species is here identified by the structure of the males gonopodium.

Introduction

Almost 45 valid species belong to the genus Gambusia  (Page et al.1991; Lydeard et al.1995; Lucinda 2003) and are widely spread in North, Central  and South America, Caribean islands included. Two of these species, specifically  Gambusia affinis (Baird & Girard 1853) and Gambusia holbrooki (Girard 1859) were widely introduced through out the whole world for mosquito population control purposes during the early 20th century. The systematic position of both species was clarified in Etnier et al., 1993 (see also Wooten et al. 1998). Italy was one of the first countries where Gambusia has been introduced as mosquito control agent in 1925 (see Stapleton 2004). Until the Seventies (1970), their presence was mainly registered in Northern Italy and along the Tirrenic shore, but during recent years, many new populations arose also along the east coast and in the South. For the same reasons, specimens have been introduced also in Spain, France, Ex-Jugoslavia, Albania, Greece and as far as the Balcanic area, Russia included (see Grimaldi & Manzoni 1990) and successively all over the world. Many articles and books report the presence of both this species, but for sometime only one is considered alive in our country, but they usually do not report any specific study or test to confirm that. For this reason and also due to our interest in the Italian killifish, Aphanius fasciatus (Valenciennes in Humboldt & Valenciennes 1821), that often share the same body of water with Gambusia, we decided to work on this topic.  The purpose of the present study is to clarify that situation, identifying the species introduced in Italy by the structure of the males gonopodium.

Material and Methods

Male specimens of 4 different populations, from all the  Italian territory (north, south and Islands), was collected with the help of hand dip net and then preserved in alcohol.

The localities of collections were: 

        Modena (Sant Anna, June 2004, 44°36’25” N 11°01’05”E ),

        Palermo (Giardino zoologico, April 2005, 38°06’56”N 13°21’40”E),

        Lecce (ponds near University, May 2005, 40°21’12”N 18°10’26”E)

        Cagliari ( collected on February 2006, Lago Poggio dei Pini, Capoterra ,  

                         39° 08' 48" N 8° 58' 29"E).

In order to examine the gonopodium, and take a photograph of it, each specimen was taken from the test tube containing the alcoholic solution and then washed with pure water. The gonopodium of each male, has been removed surgically using a bisturi and pliers for dissection, then it was put in to a little observation chamber that allowed examination through an optical microscope. The tissues were lit by a white-light lamp. The kind of image we were looking for, was obtained both using 10x and 20x objective lenses and then it was snapped with a digital camera, connected to the microscope, and then saved on the PC. The identification of the species is based on the differences of the males gonopodium structure (see Etnier et al. 1993).

Discussion

All the specimens we tested, by taking photographs of their gonopodium, show clearly that the distal segments of the most ventral element of the gonopodium, is finely serrate dorsally. Thus, even if many authors, indicate that G. affinis is the mainly widespread mosquito fish in our country, this study is definitely a clear indication that the species introduced, and still living, in Italy is G. holbrooki. The gonopodium structure is frequently used to discriminate species see as eg. Meyer&Schartl (2002), Poeser (2002) and Chambers (1987). We hope that this work may interest more people, in order to get more material and information over this topic.

Acknowledgements

We want to thank Fracesco Denitto, Federico Marrone, Michele Silvestri and Alessandro Spiga for the preserved specimens. Thanks to Daniele Cavazzoni for assistance in preparing the first draft of the manuscript

Thanks to Alessandro Tozzi and Alessandro Spiga for the pictures .

We thank the Animal Biology and Ecology department of the Università degli Studi di Cagliari, in particular Dr. Marisa Gaviano, who allowed us to work with microscopes for this research.