Ichthyological Research

, Volume 60, Issue 2, pp 142–148

Artificial reproduction and reproductive parameters of the internally inseminated driftwood catfish Trachelyopterusgaleatus (Siluriformes: Auchenipteridae)

Authors

    • Campus Ciências e SaúdeUniversidade Federal de São João Del Rei
  • Fábio P. Arantes
    • Programa de Pós-Graduação em Zoologia de VertebradosPontifícia Universidade Católica de Minas Gerais
  • Edson V. Sampaio
    • Estação de Hidrobiologia e Piscicultura de Três Marias, CODEVASF
  • Yoshimi Sato
    • Estação de Hidrobiologia e Piscicultura de Três Marias, CODEVASF
Full Paper

DOI: 10.1007/s10228-012-0324-9

Cite this article as:
Santos, H.B., Arantes, F.P., Sampaio, E.V. et al. Ichthyol Res (2013) 60: 142. doi:10.1007/s10228-012-0324-9

Abstract

The driftwood catfish Trachelyopterusgaleatus (Linnaeus 1766) is widely distributed in the São Francisco basin in Brazil, having internal fertilization as its reproduction hallmark. Since there are no studies on the artificial reproduction of T. galeatus, the aim of the present study was to induce spawning by hypophysation and to determine the reproductive parameters for this species. Thus, T. galeatus adults (12 of each sex) were treated with Cyprinus carpio pituitary homogenate (CPH) and 8 of the 12 females (67 %) responded positively to the treatment. The stripping of oocytes was carried out at 24 °C, 14 h after the application of CPH, and the average fertilization rate was 60 %. The number of stripped oocytes was 351 ± 5 oocytes g−1 with average egg diameters of 2.3 ± 0.1 and 3.3 ± 0.1 mm before and after eggs hydration, respectively. The oocytes of T. galeatus were opaque, light yellow, demersal, adhesive, and covered with a jelly coat. Data regarding egg production were also recorded for T. galeatus with an average of 8.2 ± 1.4 (%) for the stripped oocyte index and 3,163 ± 1,011 oocytes for total fecundity. The initial and final embryo survival rate was of 2,491 ± 953 and 1,527 ± 670 embryos, respectively. Larval hatching took up to 127 h after fertilization at 24 °C where the larvae presented a mean total length of 4.2 ± 0.1 mm. The findings obtained for T. galeatus demonstrated the success of artificial reproduction and the first description of reproductive parameters such as fecundity, embryo survival rate, and egg biology for this species.

Keywords

Induced spawningHypophysationInternal fertilizationEmbryo survival rateFecundity

Introduction

The Auchenipteridae, or driftwood catfish, are Neotropical siluriforms, distributed primarily in river systems from Panama to Patagonia, Argentina (Akama and Sarmento-Soares 2007). In the Auchenipteridae, the most common genera are Auchenipterichthys and Trachycorystes (Buckup et al. 2007; Ferraris 2003), and the driftwood catfish Trachelyopterusgaleatus (Linnaeus 1766) is widely distributed in South America. It is common in the São Francisco basin, being known popularly as driftwood catfish. The driftwood catfish are usually nocturnal, although they may be active at sunset. The species is omnivorous, feeding on a large amount of fruits, seeds, and terrestrial arthropods (Andrian and Barbieri 1996; Ferraris 2003; Santos 2005). The driftwood catfish are unique among the Siluriformes because they present internal fertilization and marked sexual dimorphism, males showing a modification in the form of an intromittent organ on the first ray of the anal fin. Moreover, the females have a saclike structure in the oviduct where spermatozoa are stored after copulation, and fertilization occurs only at the moment of spawning (Ferraris 2003; Meisner et al. 2000).

During the last few decades, natural fish populations have declined because of environmental degradation and over-fishing. This has been observed in the São Francisco basin because species of great commercial importance such as Brycon orthotaenia (matrinxã), Salminus brasiliensis (dourado), Conorhynchos conirostris (pirá), Lophiosilurus alexandri (pacamã), Pseudoplatystoma corruscans (surubim) and Rhinelepis aspera (armored catfish) have been captured less frequently over the last few decades (Sato et al. 2003a). This has led to an increased demand for techniques that aid the production of fish in conservation hatcheries (Sato et al. 2003a). Hormonal assays are widely used for the induction and synchronization of spawning in public hatcheries (Sato et al. 2003a; Sampaio and Sato 2006; Kujawa et al. 2011). Artificial reproduction of teleosts using pituitary hormones (hypophysation) has been established for several decades, mainly for species that do not reproduce spontaneously in captivity (Woynarovich and Horváth 1980; Sato et al. 1999; Sampaio and Sato 2006).

Fecundity of species is related to the intensity of annual recruitment and reproductive success (Csirke 1980). The evaluation of fecundity provides data for the estimation of natural fish stocks and the production of fingerlings (Araújo and Garutti 2002). Moreover, it can help understand the life strategy of the species, such as definition of reproduction style or maturation period (Andrade et al. 2010). Total fecundity is defined as the number of oocytes released plus the number of oocytes retained in the ovaries during the reproductive period, since relative fecundity is related to female body weight or length (Sato et al. 2003a). For various reasons, the expected oocyte number in spawning is usually higher than the production of fingerlings (Sampaio and Sato 2006). Thus, another biological variable is the embryo survival rate, which acquires practical importance in hatchery stations, since it indicates the oocyte number actually spawned per batch or per reproductive period that can reach the larval stage (Sato et al. 2003a). Therefore, the understanding of the fecundity and embryo survival rate of a species becomes an important tool that can be applied in aquaculture.

Several studies have been developed for T. galeatus such as morphological and morphometric descriptions of the developmental stages (Chacon and Mendes-Filho 1972; Sanches et al. 1999), reproduction and morphology of the genital tract (Medeiros et al. 2003; Parreira et al. 2009; Melo et al. 2011), and feeding ecology (Adrian and Barbieri 1996; Alvim and Peret 2004; Santos 2005). Although there are studies regarding the biology of T. galeatus, work describing the artificial reproduction and reproductive parameters has still not been done for this species.

Since biological information about induced spawning and reproductive aspects of T. galeatus is unknown, the goal of this study was to carry out artificial reproduction of the driftwood catfish by hypophysation in order to obtain the reproductive parameters that will provide essential biological data that can be applied to the management and conservation of this species.

Materials and methods

Breeding management. All experimental assays were performed at the Hydrobiology and Hatchery Station of Três Marias (18°11′58″S, 45°15′07″W), Minas Gerais, Brazil, in accordance with the Guidelines for Animal Experimentation established by the Brazilian College for Animal Experimentation (COBEA). The broodstock population of Trachelyopterus galeatus was captured in the marginal ponds of the Paracatu River and kept for at least 1 year in a 600 m2 pond at a stocking rate of 1 kg of fish in 5 m−2. The experiment was carried out during the reproductive period of 2003/2004, and the animals were fed with commercial pelleted feed (22 % crude protein and 10 % fat NUTRON), 1.5 % of body weight day−1, 5 days week−1.

Breeders were selected for hypophysation considering their external sexual characteristics: females with a protruding and reddish urogenital papilla and a flaccid abdomen, and males that released sperm when handled (Sato et al. 2003a). Thus, 24 animals were selected, 12 of each sex. The selected fish were weighed, measured, transferred, and kept separated by sex in concrete tanks with a capacity of 2.4 m3 each (3.0 × 1.0 × 0.8 m). The tanks, supplied with continuous water flow (15 l min−1), had the following physical characteristics, maintained throughout the experiment: temperature adjusted to 24 °C, dissolved oxygen = 5.9–6.2 mg l−1, conductivity = 72–76 μS cm−1, and pH = 6.8–7.2.

Induced spawning assay. For the hypophysation assay, all specimens (males and females) of T. galeatus were induced to spawn with Cyprinus carpio (common carp) pituitary homogenate (CPH). The CPH was prepared according to Woynarovich and Horváth (1980): dried carp pituitaries (Agrober, Budapest, Hungary) were macerated in glycerin, followed by homogenization in physiological saline solution (0.7 % NaCl). Females and males received injections of the CPH (5.0 ± 0.5 mg kg−1 body weight) administered intraperitoneally under the ventral fin. The fish were checked 8 h after the injection application and later every hour. Gamete maturation was regularly monitored by observing the behavior of the breeders, palpation of the abdomen of the females, and checking the oocytes released into the water. The time spawning was determined through hours-grade (HG), considering the temperature of the water and the time lapse until spawning happened.

Fertilization and incubation. Oocytes and sperm were obtained by extrusion and dry fertilization was performed. The fertilized eggs were placed in 20-l funnel-type fiberglass incubators (Woynarovich 1986) that received about 10 g of ova. The water (1.5–3 L min−1) in the incubators presented the following physical-chemical characteristics: temperature 23.0–25.0 °C, dissolved oxygen 5.9–6.2 mg l−1, pH 6.8–7.2 and conductivity 72–76 μS cm−1.

Total fecundity was determined considering the total number of oocytes (stripped oocytes plus released oocytes and oocytes retained in the ovaries). The oocyte number per gram of ova was also obtained by counting fresh oocytes present in about 2 g of ova samples. Additionally, the stripped ova index was calculated using the following formula (SOI = stripped ova weight 100 BW−1 where BW = body weight). For each female, the gonadossomatic index was also calculated (GSI = GW100BW−1, where GW = ovary weight). The initial embryo survival rate (number of oocytes per stripped ova) and the final embryo survival rate (number of viable embryonic eggs counted after blastopore closure) were calculated using 200 eggs collected from the middle section of the incubators. The degree-hours at hatching were obtained from the sum of the incubator water temperature taken every hour from the time of the hydrated egg until hatching. Moreover, relative fecundity and embryo survival rate were estimated in relation to the total length and body weight for T. galeatus.

Histology and morphometry. For histology, mature ovaries and testes samples were fixed in Bouin’s solution for 6–8 h at room temperature. The specimens were embedded in paraffin, sectioned at a thickness of 3–5 μm, and stained with hematoxylin-eosin.

Sixty eggs for each female (non-hydrated and hydrated) were used to measure the vitelline sac diameters, the width of the perivitellinic space and the chorion thickness using a stereoscopic microscope coupled to an ocular micrometer. Moreover, egg pigment and presence or absence of a gelatinous coat were also recorded.

The total length (mm) of newly hatched larvae was measured using 60 larvae in a stereoscopic microscope coupled to an ocular micrometer. The terminology of larvae and post larvae used in this study followed Woynarovich and Horváth (1980), who considered post larvae after the opening of the mouth.

Statistical analysis. Descriptive statistics and linear regression for biological parameters, such as total fecundity, initial and final embryo survival rate, total length and body weight were performed using GraphPad InStat (Software Inc., version 3.05, San Diego, CA, USA), and the values were expressed as mean ± standard deviation (SD).

Results

Trachelyopterus galeatus reached gonadal maturation for hypophysation between October and February, coinciding with the local rainy season. The 12 males treated (16.2 ± 1.0 cm total length; 65.0 ± 9.0 g body weight) were easily handled, and when they were kept in the experimental tanks secondary sexual character (i.e., emission of sounds) was not observed. Eight of the 12 females (17.1 ± 1.9 cm total length; 84.0 ± 24.0 g body weight) responded positively to the hypophysation (i.e., about 67 %), producing healthy oocytes. The females of T. galeatus did not adequately signal the spawning moment and presented GSI from 9.1 to 12.2 %. The females that had not ovulated presented the following biometric data: 15.2 ± 1.3 cm total length; 60.8 ± 10.1 g body weight, and GSI 9.2 ± 0.9 g.

Macroscopically, the T. galeatus ovaries and testis (fringed morphology) are paired organs where the ovarian and the spermatic ducts open into the urogenital papilla. The mature ovaries were bulky, highly vascularized, yellowish, and presented large vitellogenic oocytes observable macroscopically (Fig. 1a). Microscopically, the mature ovaries presented initial (O1, O2), pre-vitellogenic (O3) and vitellogenic (O4) oocytes (Fig. 1b). The O4 presented acidophilic yolk globules widespread throughout the ooplasm. Mature testes were whitish, voluminous, turgid, and highly vascularized with spermatogenic fringes, and lobes of the seminal vesicles were well developed (Fig. 1c). The histological analyses of the mature fringed testis (Fig. 1c) showed seminiferous tubules filled with sperm and spermatogenic cells (Fig. 1d).
https://static-content.springer.com/image/art%3A10.1007%2Fs10228-012-0324-9/MediaObjects/10228_2012_324_Fig1_HTML.jpg
Fig. 1

Macro and microscopic morphology of the ovaries (a, b) and testis (c, d) of the mature Trachelyopterus galeatus. a The mature ovaries were bulky, highly vascularized, yellowish, and presented great vitellogenic oocytes. b Histological section of the mature ovary showing vitellogenic oocyte (O4) characterized by the presence of acidophilic yolk globules (Y) throughout the ooplasm. Moreover, the initial (O1, O2) and pre-vitellogenic (O3) oocytes are also observed in section. c Mature testis are whitish, turgid, and vascularized, presenting fringes well developed (arrowheads), and secretory lobes (arrows) of the seminal vesicle. d Mature testis showing seminiferous tubules (ST) filled by spermatozoa (SPZ). Bars 1 cm in a and c, stained with H&E, and bars 100 μm in b and d

Ovulation occurred about 14 h after the dose of CPH with water temperature at 24 °C, corresponding to cumulative thermal units of 325–350 degree-hours (335 ± 10). The oocytes of T. galeatus were opaque, light yellow, demersal, adhesive, and covered with a jelly coat. After fresh stripping, the non-hydrated egg diameters were about 2.4 mm, increasing to 3.4 mm after hydration. Other findings regarding the egg characteristics, such as the perivitellinic space width, the chorion thickness, and the yolk sac diameter, are summarized in Table 1.
Table 1

Means of the non-hydrated and hydrated egg diameter, yolk sac diameter, perivitellinic space width, chorion thickness, and larvae total length after induced spawning in Trachelyopterus galeatus

Egg measurements

N

Mean ± SD

Range

Non-hydrated egg diameter

60

2,323 ± 51 μm

2,233–2,389 μm

Hydrated egg diameter

60

3,380 ± 85 μm

3,246–3,506 μm

Yolk sac diameter

60

1,673 ± 69 μm

1,558–1,766 μm

Perivitellinic space width

60

448 ± 39 μm

402–506 μm

Chorion thickness

60

405 ± 41 μm

338–467 μm

Larvae total length

60

4.2 ± 0.1 mm

4.0–4.3 mm

N number of measured structures

Data regarding biological parameters, such as the average number of oocytes per gram of ova, stripped ova index, egg fertilization rate, total fecundity, and initial and final embryo survival rate after induced spawning in T. galeatus, are listed in Table 2. In the present study, the oocyte number per gram of ova ranged from 342 to 358. The stripped ova index (%) was also obtained within values of 6.8–10.1. The total fecundity ranged from 1,505 to 4,651 oocytes. The average rate of egg fertilization was 60 %. Moreover, the average embryo survival rate was also obtained, where initial the embryo survival rate reached 2,491 eggs, while the final embryo survival rate (after blastopore closure) was 1,527 embryos, occurring about 18 h after fertilization. Finally, a linear relationship between total fecundity, initial and final embryo survival rate in relation to total length (Fig. 2) or to body weight (Fig. 3) was also found for T. galeatus.
Table 2

Means of the oocytes number per gram of ova, stripped ova index, gonadosomatic index, egg fertilization rate, total fecundity, and initial and final embryo survival rate after induced spawning in Trachelyopterus galeatus

Parameters

N

Mean ± SD

Range

Oocytes number per gram of ova

8

351 ± 5

342–358

Stripped ova index (%)

8

8.2 ± 1.3

6.8–10.1

Gonadosomatic index (%)

8

10.6 ± 1.2

9.1–12.2

Egg fertilization rate (%)

8

60 ± 5

50–69

Total fecundity

8

3,163 ± 1,011

1,505–4,651

Initial embryo survival rate

8

2,491 ± 953

1,015–3,941

Final embryo survival rate

8

1,527 ± 670

511–2,723

N female number

https://static-content.springer.com/image/art%3A10.1007%2Fs10228-012-0324-9/MediaObjects/10228_2012_324_Fig2_HTML.gif
Fig. 2

Linear relationship of relative fecundity (RF), initial (IESR) and final (FESR) embryo survival rate with total length (TL), obtained simultaneously from eight Trachelyopterus galeatus females submitted to hypophysation at Três Marias Hydrobiology and Hatchery Station during the reproduction cycle of 2003–2004

https://static-content.springer.com/image/art%3A10.1007%2Fs10228-012-0324-9/MediaObjects/10228_2012_324_Fig3_HTML.gif
Fig. 3

Linear relationship of relative fecundity (RF), initial (IESR) and final (FESR) embryo survival rate with body weight (BW), obtained simultaneously from eight Trachelyopterus galeatus females submitted to hypophysation at Três Marias Hydrobiology and Hatchery Station during the reproduction cycle of 2003–2004

The time of larval hatching of T. galeatus ranged from 125 to 129 h in water temperature of 24 °C, corresponding to 3,020–3,096 degree-hours (3051 ± 28). The larvae of T. galeatus showed no adhesive organs and an absence of vertical movements in the water column. Moreover, newly hatched larvae presented an average total length of 4.2 mm with a range of 4.0–4.3 mm.

Discussion

This study describes important biological findings regarding artificial reproduction and reproductive parameters of driftwood catfish, which presents internal fertilization. Although internal insemination is a peculiar reproductive strategy of Trachelyopterus galeatus, the present study showed that induced spawning by hypophysation in this species can be considered satisfactory since 67 % of the females released healthy oocytes that were fertilized using dry methodology. The response of driftwood catfish females to hypophysation was similar to that obtained for other siluriform species, which was 71 % in Rhamdiasapo (see Espinach Ros et al. 1984), 58.3 % in Pseudoplatystoma corruscans (see Sato et al. 1997), 70.4 % in Pimelodusmaculatus (see Sato et al. 1999), and 75 % in Pseudopimelodus charus (see Sampaio and Sato 2006). The T. galeatus females did not adequately signal the spawning moment. The non-signalling described for driftwood catfish appears to be a common feature among the Siluriformes, such as that observed for Pseudoplatystoma corruscans (see Sato et al., 1997), Pimelodusmaculatus (see Sato et al. 1999) and Pseudopimeloduscharus (see Sampaio and Sato 2006).

Since water temperature is an important parameter for biological systems, the degree-hours (i.e., relationship between time and water temperature) become an important biological tool to estimate the ovulation and larvae hatching time in hatchery stations. The extrusion of oocytes of T. galeatus was performed with an average of 335 degree-hours (i.e., about 14 h) after application of the CPH at 24 °C. These results were different from those obtained in other Neotropical siluriforms submitted to similar temperature conditions (at 24 °C): 1,022 in Rhinelepis aspera, 394 in Pimelodus maculatus, and 489 degree-hours in Pseudoplatystoma corruscans (see Sato et al. 2003a). The eggs of T. galeatus were spherical, opaque, demersal, and yellowish. The light yellow color observed in oocytes of T. galeatus is a common characteristic present in other siluriform species (Sato et al. 2003b). The yellow and orange colors of the oocytes characterize the presence of carotenoid pigments of great functional importance, because they constitute endogenous sources of oxygen and energy for embryo development (Balon 1977; Kitahara 1984, Sato et al. 2003b). The oocytes of T. galeatus presented adhesiveness and a gelatinous layer, both of which have also been described in other siluriform species: Rhamdia hilarii (see Godinho et al. 1978), Rhamdia sapo (see Espinach Ros et al., 1984), Rhamdia quelen, and Rhinelepis aspera (see Sato et al., 2003b). The presence of a gelatinous layer appears to be a common feature in siluriform eggs. The gelatinous adhesive layer allows eggs to adhere to structures present in river and lake systems (Riehl and Patzner 1998). However, a gelatinous layer without adhesiveness can occur in eggs of other Neotropical siluriforms, such as Pseudoplatystoma corruscans, Pseudopimelodus charus, Pimelodus maculatus, and Rhamdia quelen (see Sato et al., 2003b). Non-hydrated eggs of T. galeatus presented an average diameter of 2.3 mm, and after hydration the average diameter increased to 3.4 mm, representing a rise of about 46 %, which can be considered large when compared to eggs from other siluriform species: Rhamdia quelen (1.5–2.6) and Pseudopimelodus charus (1.7–2.7) (Sampaio and Sato 2006).

Morphometric data regarding the width of the perivitellinic space (448 ± 39 μm), yolk sac diameter (1,673 ± 69 μm) and chorion thickness (about 405 ± 41 μm) were measured for T. galeatus. The chorion thickness in newly fertilized eggs of driftwood catfish was relatively large when compared to other teleosts: Pimelodus maculatus (about 248 μm) (Sato et al. 1999), and values were close to those obtained for other catfish species such as Pseudopimelodus charus and Rhamdia quelen (about 425 and 506 μm, respectively) (Sampaio and Sato 2006). A very thick chorion, as observed in T. galeatus, can act as a protection mechanism for the embryo against environmental adversity (Riehl and Patzner 1998). Average diameter of the yolk sac (1,673 ± 69 μm) in T. galeatus was higher compared with other siluriform species: 694 μm in Pimelodus maculatus (see Sato et al. 1999), 1,058 μm in Pseudopimelodus charus, and 955 μm in Rhamdia quelen (see Sampaio and Sato 2006). These findings regarding yolk sac diameter for driftwood catfish suggest that this species invests significantly in the nutritional reserve for embryo development (Riehl and Patzner 1998).

Regarding oocyte number in relation to ova weight, T. galeatus presented an average of 351 oocytes g−1, which is a much smaller value than that found for other siluriformes, such as Pseudoplatystoma corruscans with 2,554 (Sato et al. 2003a), Rhamdia quelen and Pseudopimelodus charus with 1,128 and 1,073, respectively (Sampaio and Sato 2006), and Pimelodus maculatus with 3,276 oocytes g−1 of ova (Sato et al. 1999). The GSI for mature females of T. galeatus ranged from 9.1 to 12.2 %, and the average value was about 10.6 ± 1.2. Usually, mature females of siluriform species exhibit GSI values between 7 and 20 % (Sato et al. 2003b; Vazzoler 1996).

Fecundity studies are important tools for the successful management and conservation of fish stocks, but there is a paucity of current fecundity data for many species (McCarthy et al. 2008). The total fecundity of T. galeatus ranged from 1,505 to 4,651 oocytes, which is much smaller than that found for other Neotropical catfishes: 24,640–134,176 in Pseudopimelodus charus and 16,750–79,886 in Rhamdia quelen (see Sampaio and Sato 2006), 80,120–205,206 in Pimelodus maculatus (see Sato et al. 1999), and 81,900–347,604 oocytes in Rhinelepis aspera (see Sato et al. 1998). The embryo survival rate for T. galeatus was 60 %. These values can be considered satisfactory when compared to those obtained in other siluriforms, which were about 61 % in Rhamdia sapo (see Espinach Ros et al. 1984), 70.4 % in Pseudoplatystoma corruscans (see Sato et al. 2003a), 64 % in Pimelodus maculatus (see Sato et al. 1999), 72 % in Rhinelepis aspera (see Sato et al. 1998), and 75 % in Rhamdia quelen and Pseudopimelodus charus (see Sampaio and Sato 2006).

Spawning type is the way in which females release oocytes within the reproductive period and can be classified as single or multi-batch spawning. In general, in Neotropical regions, single spawning is observed in migratory species that inhabit lotic environments without parental care. On the other hand, multi-batch spawning is a common characteristic of species that inhabit lentic environments such as lakes, ponds, and reservoirs (Bazzoli 2003). In induced spawning assays, it has been observed that single spawning species exhibit synchronous oocyte development, high fecundity, eggs without adhesiveness, and fast embryonic and larval development (Sato et al. 2003b). In this study, T. galeatus was characterized as having multi-batch spawning, presenting asynchronous oocyte development, low fecundity, adhesive eggs, and slow embryo development.

Hatching in T. galeatus was on average 3,051 degree-hours (about 127 h) after egg fertilization at 24 °C, which is quite a long time when compared to other Neotropical catfishes that present adhesive and large eggs: 1,099 (about 45.8 h) in Franciscodoras marmoratus and 1,022 (about 43 h) in Rhinelepis aspera degree-hours (Sato et al. 2003b). However, in siluriform species that produce free eggs, the hatching period occurs in a shorter time, for example, 27 h at 23 °C in Rhamdia hilarii (see Godinho et al. 1978), 30–45 h at 22–24 °C in Rhamdia sapo (see Cussac et al. 1985), 16 h at 24 °C in Pimelodus maculatus (see Sato et al. 1999), and 20 h at 24 °C in Pseudoplatystoma corruscans (see Sato et al. 2003a), 499 (about 21 h) in Pseudopimelodus charus and 492 degree-hours (about 21 h) in Rhamdia quelen (see Sampaio and Sato 2006).

Regarding larval biometry, the T. galeatus larvae measured on average 4.2 mm in total length. Length of the driftwood catfish larvae was large compared to several siluriform larvae: 2.8–3.5 mm for Rhamdia quelen and 3 mm for Pseudopimelodus charus (see Sampaio and Sato 2006), 2.6 mm for Pimelodus maculatus, and 2.9 mm for Pseudoplatystoma corruscans (see Sato et al. 2003b). In this study, the T. galeatus larvae did not show the larval adhesive organ, and there was an absence of vertical movement in the water column. This is a common feature in the larvae of siluriform species, as previously described for Rhamdia quelen, F. marmoratus, Pimelodus maculatus, Conorhynchos conirostris, Pseudoplatystoma corruscans, Pseudopimelodus charus, and Rhinelepis aspera (Sato et al. 2003b; Sampaio and Sato 2006). In hatched larvae, the larval adhesive organ is important mainly in the adhesion and dispersion of larvae. In Neotropical species, this structure has been described in Salminus brasiliensis, Bryconorthotaenia, and Salminus hilarii, which are migratory characiforms that do not exhibit parental care, have eggs without adhesiveness, and single spawning (Sato et al. 2003b). Since T. galeatus is a sedentary species and presents multi-batch spawning and adhesive eggs, this could explain the absence of a larval adhesive organ in its larvae.

In summary, the results obtained here for T. galeatus demonstrated the success of artificial reproduction for this species. Since no studies on artificial reproduction by hypophysation have been carried out for this species nor was a description of the reproductive parameters available, the present study provided important biological information for the management, conservation, ontogeny, phylogeny, and embryology of this species.

Acknowledgments

We are thankful to the Estação de Hidrobiologia e Piscicultura de Três Marias and the Companhia de Desenvolvimento dos Vales do São Francisco e do Parnaíba, Três Marias, as well as CEMIG-GT for technical assistance in providing the facilities used for this study. The study was supported by grants from FAPEMIG (APQ 00837/08) and CNPq (No. 482826/2010-0). We are also grateful to the reviewers by their commentaries and suggestions that improved the manuscript.

Copyright information

© The Ichthyological Society of Japan 2012