SUMMARY
     Trophic ecology studies give basic and necessary information to 
understand the biological and ecological role that carries out fishes in 
ecosystems that they inhabit to establish protocols of management of their 
populations. In these studies the relationships between the species biology and 
physiology and their habitat, feedings habits, type of diet and biotic relations 
are established.
     This thesis contribute in a better knowledge of biology, phenology and 
feedings habits of five benthic fish's species of commercial interest in the 
Valencian littoral for which almost doesn't exist information. These fish's species 
are the red mullet (Mullus surmuletus), the Portuguese sole (Synaptura 
lusitanica), the red scorpionfish (Scorpaena scrofa), the stargazer (Uranoscopus 
scaber) and the common torpedo (Torpedo torpedo). This study also relates the 
importance of ecology and physiology of fishes with the incorporation of 
polluting substances like heavy metals and to know their accumulation patterns 
in different organs and tissues.
     The study area was the Cullera Bay (Spain), and the fish samples come 
from the artisan fishing landings. We carried out 30 samplings between July of 
2004 and January of 2006 in order cover all the seasons. We obtained in whole 
1102 fish of different heights, of five selected species.
     The biometric and morphological data of each species, allowed us to 
characterize the sample, to analyze its evolution across the time and to 
establish some biometric relations that helped us to explain aspects of the 
growth and nutritional and reproductive biology of each species.
     We found that those species are fished in the whole bay, of artisan form 
and with a trammel net, in a rank of depths between 6 and 20 meters, and 
throughout all the year. Their distribution and abundance are determined 
mainly by factors like the seasonal variation. Some species as S. scrofa and T. 
torpedo can display a segregation by sexes in their distribution pattern.
     With regard to the size in most of the species, 50% of the individuals have 
reached the sexual maturity before having a size of 25 cm. Over this size it is 
considered that the most of the individuals are adults and they have already 
had at least one reproduction, and below the 15 cm they are still youthful. Most 
of the species have their sexual maturity cycle and spawning in spring and early 
of the summer. These dates coincide with periods of recruitment of juvenile, 
moreover being in addition favourable for the accumulation of energetic 
corporal reserves.
     The stomachs of the fish of the selected species were examined for the 
study of the feeding habits and trophic dynamics. We determinate the vacuity 
index, weight of the stomach content, filling index or repletion index, and 
weight and average number of the preys by stomach. The trophic composition 
of the diet was studied by means of the numerical index, gravimetric index, and 
occurrence frequency of the preys and combined methods of analysis, besides 
making an evaluation of the food strategy of each species. Also, some 
morphological characters of the species, related to the feeding habits, were 
analyzed, as they are the length of the gut and the mouth area. Finally, within 
this section we studied the trophic relations between species, from the point of 
view of the dietary breadth, diversity of prey items ingested and dietary 
overlap, in order to determine the trophic level in each species.
     From the data of the diet analysis, we have verified that the fish have a 
greater feeding activity in favourable seasons. Also, the females seem to feed 
themselves more, probably by their physiological requirements for the 
reproduction. Moreover, the fishes of greater sizes usually have heavier 
stomach contents, because they have larger stomachs and bigger mouths.
     The dietary preference in the studied species were diverse, in such a way 
that M.surmuletus is fed on small but abundant preys, mainly Crustaceans 
(Brachyura and Amphipoda), and Polychaeta in smaller proportion, with a 
generalist feeding strategy. On the other hand, S. lusitanica fed almost 
exclusively on Polychaeta, consequently its strategy is clearly specialist. Of the 
three remaining species that based their feeding on fish, S. scrofa and T. 
torpedo displayed a specialist strategy and U. scaber a generalist one strategy. 
S. scrofa fed in abundant amounts of preys of average size, predominating 
fishes, crustaceans and molluscs. T. torpedo fed on preys of great size, and its 
diet is composed mainly by fishes, polychaetes and molluscs. Finally, U. scaber 
consumes preys of great size with a low number by stomach, based in fishes, 
crustaceans, molluscs and polichaetes. Of the five species, two species have 
trophic levels that correspond to omnivorous, with preference by animals (M. 
surmuletus and S. lusitanica), and three species to carnivorous, with the higher 
trophic levels, being important consumers of fishes (S. scrofa, U. scaber and T. 
torpedo).  
     Finally, in some fishes belonging to the samplings of July of 2004 and 
March of 2005, was carried out an analysis of the content of heavy metals (Cd, 
Pb, Zn and Cu). Analysis of the sediments of the bay was carried out too. 
Related to the metal levels in fishes, we observe a general trend in which the 
smaller metal concentrations are found in the muscle, and the higher in the 
liver. When comparing among the different species, we did not find a defined 
trend of accumulation for any metal, in relation to the habitat or trophic level, 
neither with the age or size of the fish. From the factors of bioaccumulation we 
cannot say that some specie accumulates more. It is necessary to emphasize 
that the lead is the less accumulated, and the others are in similar proportions. 
Even when the feeding is one of the main routes of incorporation of metals in 
the fishes, doesn't exist evidences of biomagnification in some species of the 
study, neither in any of its organs or tissues.