Initial development and feeding behavior of matrinxã Brycon amazonicus (Gunther, 1869), in laboratory
Author: Ana Carolina Souza Sampaio (Currículo Lattes)
Supervisor: Dr Mario Roberto Chim Figueiredo
Co-supervisor: Dra Marle Angelica Villacorte Correa
The objective of this work was to describe the main events that occurred during the initial development of the matrinxã Brycon amazonicus, correlating them with the feeding behavior presented by the larvae in the period from 24 to 240 h after hatching (HAE) or 10 days. The objective of the first chapter was to describe the embryonic and larval development of matrinxã, characterizing the main events that occurred up to 72 h after fertilization (HAF). The work was carried out at the Balbina Municipality of Presidente Figueiredo Fish Farming Station. The characterization was made based on stereo-microscopic, morphometric analysis and bibliographic comparison. Matrinxã eggs are free, transparent, spherical with a large perivithelin space (0.56 ± 0.3 mm). Successive cleavages give rise to cells with 64 blastomeres in the first AF hour.The gastrula, which started at 02 h and 40 min AF, was characterized by progressive cell involution and formation of the embryonic axis, culminating in differentiation of the head and tail, with 05 h and 30 min AF. Embryogenesis lasted for 3 h with formation of somites, notochord, optical vesicles, optics and otoliths, in addition to heartbeat and tail release. The larvae hatched at 10 h and 30 min AF, when the larval stage started, at an average temperature of 29.9ºC. The larvae hatched at 3.56 ± 0.46 mm in total length. Between 19 and 30 h after fertilization (HAF) we observed: 1) pigmentation and formation of the digestive tube 2) appearance of branchial arches 3) pectoral fin 4) opening of the mouth and 5) appearance of teeth. Cannibalism started at 34 HAF, with 5.7 ± 0.66 mm in total length, mouth opening 1.46 ± 0,19 mm and intense jaw movements accompanied by vertical swimming. The larva is capable of swimming, searching for and catching prey and escaping predators since 60 HAF, allowing its transfer to the hatchery nurseries. In the second chapter, the objective was to know the food selectivity of matrinxã in the period from 24 to 240 h after hatching (HAE). A mixture of zooplanktonic organisms (50 organisms / larvae) and feed was offered daily. The mixture offered was previously qualified and quantified and the fed larvae were sampled daily to check the food content in the digestive tract analyzed under a stereomicroscope. Selection by smaller organisms (Rotifers and nauplii) was not observed and there was no correlation between the morphometric measures of the larva and measures of the prey.The results show selection by live food, with preference for Cladoceri until the tenth day of life. In the third chapter the performance of the larvae was evaluated when submitted to different food treatments, in the period from 28 to 100 HAE, being: T1 = feed; T2 = zooplankton and T3 = Ration + zooplankton. T3 showed a higher specific growth rate (TBI) (2.03) and length (6.49 mm), however survival did not differ between treatments. The larvae started to eat live food or feed in the period between 40 and 43 HAE, when small proportions of the endogenous reserve (calf) remained, indicating the beginning of exogenous feeding in this period and use of live food up to 240 HAE. In view of the observed results,it is believed that a correct feeding management should consider reducing the incubation period from 72 h to 40 h, when the larvae should receive live food and food training to accept feed until the 10th day after hatching. This will possibly provide higher survival rates in larviculture.