Date of Award
Doctor of Philosophy
Black pacu Colossoma macropomum and red pacu Piaractus brachypomus are two endemic fruit and seed-eating Amazon fishes considered to be important seed dispersing agents in flooded forests. Dwindling populations coupled with the omnivorous feeding habits, rapid growth, high meat quality and commercial acceptance of these fishes has led to them becoming prime candidates for aquaculture development. However, high aquafeed prices are the prime limiting factor for the development of pacu culture in the Peruvian Amazon. The main objectives of this dissertation were: 1) to assess the effects of fish size on seed dispersal capacity of black and red Pacu; 2) to compare seed dispersal potential of these two Amazon fishes against two other seed dispersal mechanisms (anemochory and hydrochory); 3) to determine the apparent digestibility coefficients (ADC) of three local high-carbohydrate feedstuffs (yuca or cassava, plátano or plantain, and pijuayo or peach palm) in black and red Pacu; 4) to examine the feasibility of incorporating cassava, plantain, and peach palm meal in formulated diets for black pacu; and 5) to evaluate and compare black pacu fingerling growth, feed utilization and survival when reared at three water temperatures: 27.5, 30 and 32.5 ºC. In the first study, no significant differences were found for germination rates of seeds ingested among the three different size groups of fish tested. Although germination rates varied, the findings demonstrate both fish species in different ages may play an important role as seed dispersers in the floodplain forests. In a second study, ADC for crude protein, lipid and gross energy from raw and cooked green plantain meal (GPM) and cassava root meal (CRM) were lower compared to values of other common vegetal ingredients like corn and wheat. However, ADC values for raw and cooked peach palm meal (PPM) were, in most cases, higher than those reported for raw or cooked GPM and CRM. In comparison with other traditional feedstuffs, ADC values for PPM are similar to corn and higher than those reported for soybean meal and wheat bran, which suggests this ingredient, has high potential for incorporation in low-cost pacu aquafeed formulations in the Peruvian Amazon. In a third study, weight gain, feed conversion, survival, hematocrit, hemoglobin, mean corpuscular hemoglobin concentration, alternative complement activity, and lysozyme were found to be similar among several diets tested; however, protein efficiency ratio (PER) was lower in fish fed the diet containing wheat middlings. Relative to wheat middlings, all feedstuffs tested (cassava, plantain, and peach palm meal) were effective energy sources for juvenile black pacu and can serve as carbohydrate sources in balanced aquafeeds for this species. In a fourth study, black pacu reared at 30 ºC demonstrated significantly higher final body weight, body weight gain, specific growth rate, feed conversion ratio, feeding efficiency, and PER levels than fish reared at either 27.5 or 32.5 ºC (P<0.05). No significant differences (P>0.05) were recorded for feed intake, protein intake, or condition factor. This study suggests that global temperature increase may impair the ability of pacus to efficiently utilize feed and that growth in water temperatures above 30 ºC may become limiting for this species. In summary, growing evidence suggests that over the past two decades black and red pacu populations have significantly declined as a result of human activities and over-exploitation in the Peruvian Amazon, and their substantial role as seed disperers in the flooded forests could result in serious declines of many plant and animal components of the valuable aquatic ecosystem of the Amazon basin. Therefore, aquaculture of black and red pacu in the Peruvian Amazon is an attractive option to satisfy not only the increasing demand for animal protein for human consumption, but also as a viable mitigation measure for wild fish and forestry conservation. Results from this dissertation can serve as a basis for further improvement in culture technology for these two important species.
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