The present study aims to compare results obtained through traditional spawning with those obtained through natural spawning for five neotropical species of commercial importance. After the second hormone dose, males and females were grouped in (2:1) ratios, except for L. macrocephalus, which was maintained at a ratio of (1:1) in 1000-liter tanks. The tanks were partially covered to prevent fish stress. The fish were under constant observation to evaluate behavior and note the spawning time. Spawning al- ways occurred after two or three fish maintained a synchronized swimming and their bodies became close and laterally aligned. In the P. lineatus and L. macrocephalus species, the emission of sounds by males during spawning was observed. After spawning, the eggs were re- moved with a plastic bucket that had a mesh retention of 0.5 mm to concentrate the eggs. This bucket was in- stalled at the outlet of the water tank, and the eggs were taken to the incubator. During transfer, a 500-mL beaker was used to measure the eggs by decanting the eggs into the beaker and measuring the volume marked.

The number of eggs per milliliter was determined by collecting four 3-mL samples of fully hydrated eggs from the bucket retainer using a 10-mL pipette; the samples were then counted on a petri plate . This counting was con- ducted for each spawning. After the last hormonal application, fish were continuously removed once the females begin to release the oocytes. The female was removed carefully using a towel. The extrusion was performed by collecting oocytes in a dry plastic becker. In the sequence, the sperm, which were also obtained by extrusion, was added directly over the freshly collected oocytes. After 1 to 2 minutes of mixing the gametes, water was added to promote the activation of sperm and fertilization. Once the eggs began to hydrate, they were transferred to incubators ac- cording to the recommendations of Ihering and Azevedo . A small quantity of oocytes (± 0.5 g) was removed before mixing with semen; these oocytes were weighed and fixed in 4% buffered formaldehyde solution for later quantification. During reproduction,nft hydroponic the water temperature remained between 24.0°C and 27.5°C, the pH be- tween 6.5 and 8.2 and the dissolved oxygen between 5.6 and 9.8 mg/L.Among the spawning induction techniques used for neotropical migratory fish, the use of extrusion is well documented , as it has been used to produce such commercially important neotropical species as dourado, S. brasiliensis; matrinxã, B. cephalus; tambaqui C. ma- cropomum and pacu, P. mesopotomicus.

This type of technique is widely used due to its low operational man- agement, high control of production and its status as a well-disseminated technique. Moreover, according to Bermudez, et al. , performing fertilization by extru- sion reduces egg handling, which is considered an im- portant factor in embryo development, reduces the chance of fungi appearance, increases the fertilization rate and increases the quality of future larvae. However, a disadvantage of extrusion is that it may increase the mortality rate of broodstock used, which is generally positively related to the species-specific degree of tolerance for handling. Females and males of Brycon siebenthalae show high mortality rates after induction . Catfish (Rhamdia quelen) and piauçu (L. macro- cephalus) commonly exhibit high mortality rates a few days after spawning by extrusion . For B. orbign- yanus, up to 100% broodstock mortality rates have been observed . In this study, we observed that in the four evaluated species survival rates of individuals increased with natural spawning. The survival percentage of spawning by extrusion was low, especially for B. orbignyanus, which exhibited more than 80% mortality of brood stock males and 100% of brood stock females. Survival after extrusion was related to species behaveior. L. macrocephalus presented most docile behavior in handling and had the highest survival rates after extrusion; the converse was observed for B. orbignyanus.