Nanism (dwarfism) in fish: a comparison between red mullet Mullus barbatus from the southeastern and the central Mediterranean

Abstract

The gradient of environmental conditions from west to east in the Mediterranean results in very low primary productivity in the eastern area of this sea. This impoverishment is expressed also in higher trophic levels and has been accounted for by several faunistic phenomena. One of these is 'Levantine nanism' (dwarfism); this is characterized by smaller body size of specimens in the Levantine basin compared with conspecifics in the western Mediterranean. Nanism has been hypothesized for various taxonomic groups in the Mediterranean, but no quantitative study has yet been carried out to confirm it. In the present study male and female red mullet Mullus barbatus from trawl surveys carried out along the Mediterranean coast of Israel and the Strait of Sicily were sampled. Each fish was sexed, measured for total length (TL) and aged by otolith readings. ANCOVA analyses indicated that the TL of both males and females from Israel was significantly smaller at increasing ages than conspecifics of the same age and sex from Sicily. In addition, preliminary examination of sexual maturity of M. barbatus of both sexes indicated that the Israeli fish sexually mature at a smaller size than conspecifics of the same sex from Sicily. These findings can be explained by low productivity in the Levantine basin compared with the western Mediterranean. The low and unpredictable food supply in the southeastern Mediterranean may result in a form of r-strategy of the marginal eastern populations of this species that leads to early reproduction and smaller body size. The average higher water temperature may also partly explain Levantine nanism, as it may cause more intensive metabolic processes in the southeastern population, resulting in earlier sexual maturity and cessation of growth.

Reproductive biology of pink cuttlefish Sepia orbignyana in the Aegean Sea (eastern Mediterranean)

“…The reason for this phenomenon is the unidirectional impact of 3 main environmental factors that are different between the eastern and western Mediterranean: productivity, temperature, and salinity (Sonin et al, 2007). This study, combined with previous results (Salman, 1998;Önsoy and Salman, 2005;Salman and Önsoy, 2010;Salman, 2011), testifies that Mediterranean nanism can also be seen in cephalopods.…”

“…A phenomenon of so-called Mediterranean nanism had been suggested for various taxonomic groups of fishes and invertebrates such as sponges, crustaceans, and polychaetes (Sonin et al, 2007). The reason for this phenomenon is the unidirectional impact of 3 main environmental factors that are different between the eastern and western Mediterranean: productivity, temperature, and salinity (Sonin et al, 2007).…”

“…The species has been studied in the western Mediterranean Sea (Mangold-Wirz, 1963), but not in the eastern part of this water body, which is different in many oceanographic and biological aspects (Sonin et al, 2007).…”

Spatiotemporal patterns of catch and discards of the Israeli Mediterranean trawl fishery in the early 1990s: ecological and conservation perspectives

“…3). Despite the poor Levantine fishery suppositions made in various studies (Por, 1989, Sonin et al, 2007, these values are comparable to catch and discard rates reported for the central Mediterranean (Machias et al, 2001, D'Onghia et al, 2003, Sánchez et al, 2007. Discarded biomass alone, however, cannot represent the full extent of the impact of trawling on future year classes.…”

“…This phenomenon was hypothesized by Por (1989) and demonstrated by Sonin et al, 2007 for the red mullet Mullus barbatus. The Levant is also consistently invaded by Indo-Pacific species (e.g.…”