Embryonic and LarvaL dEvELopmEnt of Jundiá ( Rhamdia quelen , Quoy & Gaimard , 1824 , piscEs , tELEostEi ) , a south amErican catfish

the jundiá (Rhamdia quelen, Quoy & Gaimard) is an endemic south american fish species. because this species supports cold winters and grows faster during warm months, it has begun to be viewed as an ideal species for fish production in southern south america. in the present study, jundiá oocytes used were obtained by extrusion from females after hormone injection. soon after hydration, the eggs were transferred to 50 L conic glass incubators, with constant and controlled water influx. samples of fertilized eggs were transferred to petri dishes and, examined under a stereoscopic microscope, were spherical, demersal, and non-adhesive with defined perivitelline space and resistant chorion. cleavage stages occurred during the first 3.5 h. after hatching, larvae were transferred to 200 L glass fiber incubators. first signs of embryo movement were observed 21 h after fertilization; larval eclosion occurred 30.5 h after fertilization. present findings may provide a basis for studies aimed at determining the complete ontogeny of jundiá and may be useful in eco-toxicological studies.

from the biological standpoint, uncovering each step of embryo and larval development is of great importance.in addition, in these stages most fish species may be more susceptible to changes in dissolved oxygen concentration, ph, salinity, alkalinity, turbidity, and particularly to water contaminants.a complete knowledge of embryo and larval development stages might be useful in studying the effect of even small amounts of water contaminants, mainly those of agricultural origin that eventually reach water springs or ponds used for fish culture, a quite common occurrence in agricultural areas such as those in southern brazil.in this study, the main objective was to examine the initial stages of embryo and larval development of jundiá under controlled conditions.mAterIAl And methods the present work was carried out at facilities of the university of passo fundo, rio Grande do sul, southern brazil (687 m asl), using cultured females and males weighing respectively 685 ± 50 g and 500 ± 33 g. after capture, fish were quickly transferred to the laboratory and weighed.hormonal induction of ovulation was performed using pituitary extract injection according to a routine protocol (ittzés et al., 1999).the oocytes used were extruded by females within a 9 h 30 min-10 h 55 min period after pituitary extract injection.Extracted oocyte wet weights ranged from 68 g to 118 g. following weighing, oocytes were placed in petry dishes.collected by abdominal pressure, 10 mL of mixed semen from three males was added to each batch of eggs and gently mixed in; 100 mL of water was added to promote sperm activity, and egg fertilization and hydration.soon after hydration, the eggs were transferred to 50 L conic glass incubators, with constant and controlled water influx at flow rates of 0.7 mL min -1 at a temperature of 24 ± 1 °c.depending on the developmental phase, samples of fertilized eggs were taken with a plastic tube at different intervals from the incubators.during the first 2 h 43 min, egg samples were removed at approximately 15 min intervals, placed in petri dishes, and examined under a stereoscopic microscope (3.2 and 6.4 x magnification) equipped with a digital camera.
after hatching, the larvae of each egg batch were transferred to a 200 L glass fiber incubator filled with aerated water at an influx rate of 8-10 L min -1 .Larval development was analyzed from hatching until the time (92 h 45 min after hatching) that they were stocked in a previously fertilized pond (barcellos et al., 2004).
Water-quality parameters measured in incubation and larviculture were: temperature (at each sampling), dissolved oxygen, alkalinity, ph, turbidity, and total ammonia concentration (colorimetric methods and titulation, before beginning of experiment).

results
during embryonic development observation, eggs were kept in glass incubators under moderate agitation by influx at a rate of 180 L/h of water having the following characteristics: mean temperature, 24 ± 1 °c; dissolved oxygen level, 6 mg L -1 ; alkalinity, 19 mg L -1 ; ph, 6.8; turbidity, 3 L ntu; total ammonia concentration < 0.001 mg L -1 that on a ph-temperature conversion table indicated 0.0006 mg L -1 of un-ionized ammonia.
initial jundiá development of was divided into two phases: embryonic and larval.a sequence of the most important events observed in each phase is shown in figs 1-2 and table 1.
Eggs of R. quelen were spherical, demersal, and non-adhesive with a clearly defined perivitelline space and resistant chorion.cleavage stages occurred during the first 3.5 h.first signs of embryo movement were observed 21 h after fertilization; larval eclosion occurred 30.5 h after fertilization.

dIscussIon
as previously indicated, this study showed that the eggs of Rhamdia quelen were spherical, demersal, and non-adhesive, similar to those described by Godinho et al.(1978) for another fish of the same genus, i.e., Rhamdia hilarii, and for another siluriform fish, the Pseudoplatystoma coruscans as described by cardoso et al. (1995).
the perivetelline space in newly fertilized ova of R. quelen was relatively smaller than those of other teleosts, e.g., the piabanha (Brycon insignis steindachner) (andrade-tamelli et al., 2001) and similar to that found by Godinho et al. (1978) for the siluriform Rhamdia hilarii.a larger perivetelline space in some fish species may be understood as an embryo defense against environmental adversities and contributes to higher survival rates in lotic environments (Lake, 1967;matsuura, 1972).thus, the characteristics of R.quelen ova fit this species' preferred reproduction sites, which have clear water with little flow (Gomes et al., 2000).
the time required in R. quelen to form the first segmentation line in the ovum after fertilization (1 h 15 min), was very similar to that previously described for the same species (ihering & azevedo, 1936), similar to that described for Rhamdia sapo (matkovic et al., 1985), and also to that of Rhamdia hilarii, a silurid species of the genus Rhamdia (Godinho et al., 1978).on the other hand, it was shorter than found for Pimelodella lateristriga, a siluriform fish of the Rhamdia genus (ihering and azevedo, 1936).
in the present work, hatching of jundiá eggs occurred 30 h 5 min after fertilization at 24 °c, which is very similar to the period found for R. sapo (30 h, 22-24 °c; cussac et al., 1985). in contrast, in the first documented research on embryonic and larval development of jundiá (ihering and azevedo, 1936), this period varied from 35 to 46 h after fertilization at 18-19 °c. in Rhamdia hilarii, the hatching time was 27 h at 23 °c (Godinho et al., 1978).the difference in hatching time might be due to environmental conditions like water, temperature, alkalinity, ph (cussac et al., 1985), and water flow. in addition, other environmental factors not detected in the water could have affected developmental period of the embryos.
during the period in which larvae were kept in 200 L glass fiber incubators, a reduction in yolk and a marked evolution in body pigmentation was observed.the fish already had an adult appearance 123 h 15 min after from fertilization, presenting dark coloration and three well-developed pairs of barbels.a similar finding was made by Godinho et al. (1978), who described Rhamdia hilarii with an adult appearance 120 h after hatching.in Pseudoplatystoma coruscans, an adult appearance was detected four complete days after hatching (santos & Godinho, 1994).

tAble 1 description of embryonic and larval development stages according to time before and after fertilization and to macroscopic characteristics found in Rhamdia quelen.
Embryonic and LarvaL dEvELopmEnt of Rhamdia quelen Braz.J. Biol., 66(4): 1057-1063, 2006