Biological monitoring of wild thicklip grey mullet (Chelon labrosus), golden grey mullet (Liza aurata), thinlip mullet (Liza ramada) and flathead mullet (Mugil cephalus)(Pisces: Mugilidae) from different Adriatic sites: meristic counts and skeletal anomalies

This paper reports on a part of PRISMA project, funded by the Italian Ministry of Education, University and Research (M.U.R.S.T.), involving the biomonitoring of fish populations in two different Adriatic Sea sites by using some integrated descriptors at organismic level (skeletal anomalies and meristic count variation). Given the scarcity of up-to-date data on biology, physical and chemical oceanography, and environmental geophysics, as well on the degree of pollution of this Sea, the goal of the project was to contribute at enhancing the knowledge on environmental biology of Adriatic Sea. In particular, this part of the project analyzed different samplings of some mullets species for the presence of skeletal malformations under the hypothesis that stressed environment should induce alteration in skeletal development pattern in fish, as indicated by many authors. So, the investigation on mullets skeletal structures was utilized to monitor two different Adriatic Sea sites, where exhaustive information (chemical analysis of water and sediment, i.e.) on environmental conditions lack. We observed a total of 2169 individuals, 79% of which were fry and the remainder sub-adults, collected during the seasonal migration in freshwater (spring and autumn 1997) by purse-seine. Chelon labrosus accounted for 18% of the samples, Liza aurata 24%, Liza ramada 22% and Mugil cephalus 36%. Fish were sampled in two Adriatic sites, Sacca di Goro (northern Italy, Po River delta) and Lake Lesina (southern Italy). Other samplings from Tyrrhenian Sea (Fiumicino, Tiber river mouth) and from an aquaculture facility (Grosseto) were used in order to obtain additional information on skeletal plasticity of Mugilidae. Observations included meristic counts and skeletal anomalies and some multi-parametric analyses were per-formed on the data set. The results showed significant differences among the type and rate of skeletal anomalies observed in the fish samples: as far as Adriatic samples are concerned, higher malformation charge was observed in the Sacca di Goro individuals than in Lesina ones. Further, L. aurata showed a non-specific skeletal pattern and the lowest frequency of deformed individual (8.6% of total observed individuals), unlike C labrosus, L. ramada and L. aurata. So, these Mugilidae species resulted to be differently affected by skeletal anomalies according to the sampling site