Dinâmica de avaliações limnológicas em sistemas de criação de peixes.

Abstract

The aim of this research was to evaluate the dynamics of the physical, chemical and biological factors in the raise of tilapias in heavily organically polluted and not polluted water, working experimentally during 120 days in fish ponds at the NUPPA/UFPB, (João Pessoa/PB/Brazil). Four earthen fish pond (300m2 and average depth of 1,0m) supplied with entrance and water exit systems opposing longitudinally received the 1.200 post reversion fry of Oreochromis niloticus, (Linnaeus, 1757), Chitralada strain, originated from artificial incubation, had been stocked fish1:1m2 in each pond totaling 300 fish with 1,0g average weight and 3,0cm length. All fed with commercial feed using a protocol recommended for the manufacturer. Two ponds were supplied with water from a heavily organically polluted lagoon, and the other pair underwater filled, all of them kept to the same level replacing the losses for evaporation and percolating. All the water sample were collected, always at 07:00/08:00hours on the surface three times week and weekly, and analyzed the parameters physical, chemical and biological characteristics in the origin and use waters of the ponds- pH, dissolved oxygen, temperature, transparency, total, fixed and volatile solids, color, electric conductivity, turbidity, BD05, COD, chloride, alkalinity, total acidity, hardness, calcium, magnesium, salinity, ammonia, nitrito, nitrate, total phosphorus, ortophosfate, sulfate, pheofitina and chlorophyll a, structure of the plankton communities, the composition and production of macroinvertebrates benthics biomass, and quantitative aspects of the growth of tilapia with emphasis in the data of growth, length and weight, fillet and residue, proximal chemical composition, and the relationship of the microbiological quality of the water, the used feed and the fish skin. The nychthemeral dynamics of the limnological variables the temperature, dissolved oxygen, pH, and transparency had been realized each fourteen days. The main meteorological variables (temperature, rainfall, insulation, solar radiation, photoperiod and winds speed) and physical, chemical and fertility analyses of the pond soil were also analyzed. The results showed that the values of pH in the four pond had been inside of range recommended as ideal for the fish culture, exceeding a little at the superior limit. The increase in total and volatile solid was observed with elapsing of the experiment, and the load of suspension organic substance in the pond was greater than the inorganic, indicating that the biological activity was more elevated. The measures of ammonia in the pond had placed below of the concentration considered lethal to the tilapia and of the inadequate value to the growth of the fish - 0,25mg, even so lethal concentration (LC50) either equal 0,5mg/L. The average of phosphorous generated in the four ponds is improper to e received by the river that cross the experimental area. The results of the nychthemeral dynamics of the limnological showed that the temperature of the pond water is in accordance with the solar radiation and the days hours, being registered the extreme temperatures on the afternoon and during the dawn. The diurnal variation of the values of dissolved oxygen discloses a standard typical, with lesser concentrations in the part of the morning and a gradual increase in the part of the afternoon. The variation of pH values had the extreme after the introduction of the fish, reaching the level of pH 10,0 remaining in this value for the first weeks, and as well as it occurred with the OD, the largest variations of pH had occurred in the daylights. The transparency of the pond water had became more reduced with the growing of the fish and with development of phytoplankton. The phytoplanktonic community structure (composition, specific richness, density, diversity, equitability, and dominance) found the identification of 35 taxons in specific and the interspecific The class of Chlorophyta was dominant in the community, with ample dispersion of the some species of Scenedesmus equally distributed in all environments, followed by the Cyanophyta, Bacyllariphyta, Euglenophyta and only one sort of Dinophyta. The results showed greater presence of phytoplankton and concentration of chlorophyll a. principally in that ones with minor SDV, explain therefore the plankton origin of the turbidity. The zooplankton community presented low diversity, typical of continental water characteristic, being rotifer+nauplius, more abundant in all the samples with cyclopoid and calanoid contribution of copepod in some collects, and also a little of cladocerans. The insects bentics reflects the littoral regions characteristics, being the Diptera (Chironomidae) more abundant, followed by the Odonata, Coleoptera (Hydrophilidae, Dytiscidae), Odonata (Gomphidae, Libellulidae), Hemiptera (Naucoridae), Ephemeroptera. In the end of the experiment five units of each pond had the stomach content analyzed, the results showed the more frequency of cianoficeas seaweed debris and fragments of ration and Diatomaceae, verifying also the presence of items of zooplancton, rotifers and eggs of Rotifera and vegetable remaining portions. The processing results showed that the percentage of the rude skin, did not differ (P>0,05) for the units created in different environments, what also is verified in relation to the average percentage of residues, and the average percentages of fillets around 28,0%. The bacteriology of the water indicates that counting of total viable bacteria was placed below of the biosecurity reference, and the effluent generated had been inside of the legislation for fecal coliformes/100ml_. The external surface of fish microbiology presented the average values of total coliformes and fecal coliformes in the pond water higher to the skin surface and, in terms of total counting of meshophilic bacteria, were evidenced that the fish raised in the pair of clean water pond had presented in washed of the surface the counting ten times shorter to the water of these ponds, in counterpoint the similarity observed in the pair of pond filled with water of the lagoon. There was a significant difference of the growth of the fish between the pair of the ponds 1 and 4 with underwater to the other pair 1 and 3 with water from na eutrophic lagoon, otherwise there was an increase of population because some fish come through from the lake. In the pond 1 and 4 the weight reach the average of 491,1 and 539,5g and 27,3 e 28,3cm of lenght. The fillet obtained was around of 28,0%, with, total skin and residue between 60,2 and 72,0%. The proximal chemical composition resulted 18,6-21,4% to protein, 78,5-78,8% to umid 0,9-1,5% to lipid ancH.1-1,3% to minerals.