Productivity and reproductive characteristics of silver arowana Osteoglossum bicirrhosum ( Osteoglossiformes : Osteoglossidae ) at Grande Lake , Putumayo basin , Peru

Due to the importance of ornamental fishing of silver arowana, as well as, Lago Grande lake as one of the main areas for capturing baby arowanas in Peru, the present study aimed to evaluate the productivity and the biologicalreproductive characteristics of the species in the lake, which is located in the lower basin of the Putumayo River and represents an area preferred by fishermen because the important populations of silver arowana inhabiting it. Analysis of population density, biometrics, sexual maturity, spawning, fecundity, sex ratio, water level of the lake and production of baby arowana were made. The study was developed between March and July of 2012 and to implement the activities of the study was important the participation of the Association of Fishermen “Fronteras Vivas”. In general, the population density extrapolated to the lake area was 1.29 fish/ha. Of these, the density of progenitors in the lake was 1.19 fish/ha. Also, male animals had total length, standard length and total weight higher than females and it was observed that the spawning period occurred in synchronization with the start of the growing of the hydrological regime. The average number of oocytes produced by females of silver arowana in the study area was 201 and the sex ratio was equilibrated. Furthermore, the study shows the capacity of production of the lake. In order to this the water lever influenced in the production of baby arowanas. It is important to continue studying the species for regulate the fishing and recover populations.


Introduction
human consumption and as a fingerling for the The development of new knowledge, as a result of ornamental trade (BROWN, 1995;CRAMPTOM, 1999; ongoing assessments of the dynamics of fisheries, shows MOREAU; COOMES, 2006; AGUDELO-ZAMORA et al., that fisheries resources are limited. Even, their contribution 2007;ALCANTARA et al., 2007;DUPONCHELLE et al., to the nutritional and socio-economic wellbeing of the 2012). growing human population could be affected for Actually, the silver arowana is increasingly popular on extractive activities (KVIST et al., 2001). In this sense, the the international aquarium fish market (MOREAU; productivity of Amazonian fisheries has been declining COOMES, 2006COOMES, , 2007ALCANTARA et al., 2007), with for the floodplain deforestation (SMITH, 1985), as well considerable economic importance to the communities as, uncontrolled fishing. This is observed on silver arowana around the fishing areas (LOWE-MCCONNELL, 1975;populations, Osteoglossum bicirrhosum (Cuvier, 1829), a KVIST et al., 2001;MOREAU;COOMES, 2006). Precisely, relative of pirarucu that enters the aquarium trade, which this species is considered one of the most important species capture declined significantly in the last years ( Amazon aquarium trade, being reported by Moreau To implement the activities of the study was important the and Coomes (2006) over 1 million fingerlings worth USD participation of the Association of Fishermen "Fronteras 560,000 exported in 2001 in Peru. Likewise, according Vivas" who control the activities in the lake with the help to Direpro-L (2007), the main zone for extraction of of the specialist of fishing of PEDICP, in order to meet fingerlings of the species in Peru, is the lower basin of the targets of the Manage Program established for the Putumayo River, being Lago Grande lake one of the species in the area. During the period of the study, an areas with higher production (PEDICP, 2007). The mainly average monthly rainfall of 251.5 mm and a maximum problem with the use of this resource is the routine killing temperature of 31.9°C and a minimum temperature of of mouth brooding adults to collect fingerlings for the 22.2°C were reported. Furthermore, it was reported an trade that may threaten wild populations, because the average relative humidity of 84.7%, being typical fish are caught from the wild (MOREAU; COOMES, characteristics of a humid-tropical environment. 2007) and cultivation in captivity is a young activity (ARGUMEDO, 2005;COSTA et al., 2009).
Population Density This species belongs to the group of the osteoglosids, Sampling areas were established with the support of which are known as the bony fishes (KUMAZAWA; a group of experienced fishermen. For this, journeys NISHIDA, 2000). It is distributed in the Amazonas, around the lake were made, between 8:00 -9:00am Essequibo and Orinoco basins (WATKINS et al., 2004;and 15:00 -16:00pm. In this, were observed and MALDONADO-OCAMPO et al., 2008;ESCOBAR et al., identified areas where groups of silver arowana were 2013), inhabits shallow, black water lakes and the littoral active during the day. At dusk, it was observed the areas zone of rivers and lakes year-round, as well as invading where those groups of silver arowanas moved. In order the flooded forest during high water periods (LOWEto this, three zones were identified in Grande Lake and MCCONNEL, 1987;SAINT-PAUL et al., 2000). defined as areas occupied by silver arowana groups Furthermore, silver arowana reaches 1 m in total length during the all day, and these zones were delineated. The and three pounds in weight, approximately (LOWEdelineated areas constituted the sampling areas for MCCONNEL, 1987), and is a predator (LOWRY et al., population census and were characterized by stand 2005) that prefers fish (AGUDELO-ZAMORA et al., 2007). near the bank and with abundant aquatic vegetation. Something important is that silver arowana has differences Silver arowana population was estimated through census in the reproductive-biological characteristics according to during the night by journey in the areas delimitated the basin that inhabits, showing different patterns in previously. Animals registered in each of the sampling fecundity, sexual maturity (RABELLO-NETO, 1999, 2002 areas were plotted on the Grande Lake total area given GUTIERREZ et al., 2009), sex ratio, spawning, as well as, the report as fish ha. With the experience of the growth parameters (DUPONCHELLE et al., 2012). Thus, the fishermen were able to identify progenitors and stage biological-reproductive differences would be very of the offspring that these progenitors incubated. important for the management of the species in a determined area.
Biometrics Due to the importance of ornamental fishing of silver Direct and indirect samples were taken. Direct arowana, as well as, Grande lake as one of the main samplings were performed twice a month with the areas for capturing the species, the present study aimed participation of fishermen by using of gillnets of 4.5'' to evaluate the productivity and the biologicaland 5'' of mesh size, put between 30 to 40min per set, reproductive characteristics in the lake during the and located in three places suggested by a group of specific year period of using of the species, contributing fishermen. Also, direct samplings were performed by to the knowledge of the species.
using arrows and the specimens were captured by journeys around the lake. The assessment of indirect 2. Material and Methods sampling consisted of the fish captured from the study This study was executed at Grande lake (2°31'10.7"S area and landed in Huapapa. Total length, standard 70°29'23.5"W), near to Huapapa community, located in length and total weight were considered. For the lower basin of the Putumayo River, Peru. This lake has determining the relationship between weight and length an elongated shape with an area of 289.12 ha and an of the studied specimens was performed a linear average depth of 5 m. Also, it belongs to the group of correlation analysis of Pearson. lentic water, which has high organic matter decomposition of the leaves of the forest, as well as low Degree of sexual maturity conductivity and a slightly acidic pH. In addition to this, The degree of sexual maturity was recorded of Lago Grande has important populations of silver females and males captured based on the scale of arowana in good conditions and its proximity to gonadal maturity proposed by Ruiz (2011). Huapapa, which is the main community in the lower basin of the Putumayo River, represents an area preferred by Subsequently, the length of first maturity was calculated fishermen, especially for fishing the baby arowanas. The by comparing the percentage of sexually mature study was developed between March and July of 2012. individuals plotted versus length. Biota Amazônia Spawning observed (7.51%) were juveniles. Furthermore, were observed that the larvae hatched by parents were in the The gonadosomatic index (GSI) was determined, so stage I. The population density extrapolated to the lake that allowed to estimate the spawning season. The area was 1.29 fish/ha. Of these, the density of formula described for the determination of GSI was: fish progenitors in the lake was 1.19 fish/ha, of which a weight (g)/weight of gutted fish (g). GSI and the water density of parents with egg into the mouth was 0.27 level in the study area were compared, to see if these fish/ha and 0.93 fish/ha for progenitors with larvae. variables were related.
Furthermore, the study showed a density of 0.10 juvenile/ha.

Fecundity
This parameter was determined by direct count of the Biometrics oocytes of females sacrificed. Relations between fertility, For biological-reproductive characteristics of silver length and weight, were made to determine if the arowana were collected 140 individuals among juvenile production of oocytes in the species was influenced by (27) and adults (113) (±7.62) in standard length and 1635.14 g (±489.87) in total weight. Male animals had total length, standard Water level of the lake length and total weight higher than females (p<0.05 in The initial value was measured with the Garmin GPS, all three cases). Etrex10 model, by recording the height provided by the The linear correlation analysis of Pearson between equipment to the water level in the lake. From that value standard length and weight of silver arowana indicated recorded was placed a measuring rod and it was that it was a strong positive correlation between the both checked daily at 06:00am for measuring the increase or 2 variables analyzed (r=0.85, p<0.05, R =0.72) decrease of the water level. Furthermore, quality water (Graphic 1). This result showed that as the fish grew in of the lake was determined by analyzing monthly water length so did in weight too. As the correlation analysis temperature (°C), water transparency (cm), pH, dissolved made included gravid females, which could influence the oxygen (mg/L), free carbon dioxide (mg/L), ammonia erroneous result since had greater weight for the ovaries (mg/L), alkalinity (mg/L) and total hardness (mg/L).
filled, linear correlation analysis of Pearson was made, excluding gravid females, existing a strong positive Production of baby arowana correlation between standard length and weight 2 Extraction values of baby arowanas from the lake (r=0.852, p<0.05, R =0.726). during the 2012 campaign were recorded. Likewise, the stage and the number of larvae per parent were recorded based on the next characteristic: The larvae 1 (stage I) are called "lying" with yolk sac, initially are transparent and have no proper movement, with a weight of about 1 g and diameter of 10 mm. The larvae 2 (stage II) are called "swimmer" and reaches sizes greater than 35 mm long, the yolk sac represents approximately 20% of their body weight with a tendency to disappear, has proper movements for swim and float. The length and weight of the progenitors (at least for 50%) were recorded. Also, was made an analysis of mortalities of larvae and fingerlings taken from the lake during the fishing period. The linear correlation analysis of Pearson between the standard length and the number of oocytes showed no association with á=0,05.

Population Density
Degree of sexual maturity In this study, 373 individuals of silver arowana were counted in the lake, of which 92.49% were adult parents.
The size of silver arowanas observed with sexual Of these adult parents, 20.64% were parents with egg maturity ranged 53-78 cm in total length and 51-74 cm in into the mouth and 71.85% were parents with larvae into standard length for females and for males between 59the mouth. Only a small percentage of individuals 84 cm and 56-80 cm in total length and standard length, Figure 1. Degree of association between standard length (cm) and weight (g) of silver arowana, Osteoglossum bicirrhosum, Lago Grande lake. Biota Amazônia respectively. The length of first maturity for silver arowana Fecundity population in the study area, occurred at about 58 and 62 The average number of oocytes produced by females cm in standard length for females and males, respectively of silver arowana in the study area was 201. The minimum (Graphic 2); size in which 50% of the individuals observed number of oocytes recorded was 115, belonging to a were sexually mature.
female of 58 cm total length, 56 cm standard length and total weight of 1100 g. The maximum number of oocytes was 265 registered for a female of 61 cm total length, 58 cm standard length and total weight of 1450 g. The linear correlation analysis of Pearson between the standard length and the number of oocytes showed no association (r=0.207, p>0.05) (Graphic 4). This meant that the number of oocytes produced per female of silver arowana was not related to length. Likewise, the linear correlation analysis of Pearson made between the total weight of the fish and the number of oocytes, indicated that there was a weak positive correlation between the variables (r=0.465, p<0.05) (Graphic 5).

Spawning
Females with an average total length of 50.92 cm (±3.75), an average standard length of 48.58 cm (±3.45) and an average total weight of 1045.83 g (±172.49) were immature and presented low GSI (0.23±0.08). Females with total length of 67.29 cm (±4.75), an average standard length of 64.41cm (±4.35) and an average total weight of 1945.88 g (±458.98) were mature and had high GSI (5.14±1.30) due to the presence of oocytes in the ovary. Post-spawning females showed low values of GSI (0.51±0.20) and an average total length of 66.23 cm (±5.82), an average standard length of 63.44 cm (±5.75) and an average total weight of 1676.74 g (±421.36), indicating that they had traces of oocytes. The ANOVA indicated that there was no significant difference between the values of total length and standard length of mature and post-spawning females (p>0.05). With regard to the monthly variation of GSI in relation to the hydrological regime, we observed that the decline of the spawning period was between April and May. Also, it was observed that the spawning period occurred in synchronization with the start of the growing of the hydrological regime (Graphic 3).

Sex ratio
The 48.57% of the fish caught were males and 51.43% were females (n=140). That is because there was a tendency of effort concentration on silver arowana males, because they are captured for removal the baby arowanas. Otherwise, to submit the results to the chi-square test, it was observed that there was no significant difference between the proportions of both sexes, being the sex ratio 1:1 (p>0,05).

Measuring the water level
The minimum value was recorded in March with an average of 6.96 m and the maximum value in April 4. Discussion with 8.38 m on average. Likewise, a decrease in water There is no reliable scientific information reporting level was observed in May and June, and then the level population density of silver arowana in water bodies, water increased again in July. That fact did not allow being this study the first. In this regard, Tresierra and the use of the resource by the fishermen, because the Culquichicon (1993) mentioned that it is difficult to increased water level influenced to the dispersion of estimate fish densities in natural systems; however, this parents with larvae into the mouth to the flooded species inhabits identifiable areas within the lake areas in the lake (Graphic 6). All parameters allowing a reliable report. Also, the maximum length analyzed were within the appropriate range for the reported in this study for both females and males was development of the species in the wild (Table 1).
lower than that reported in other studies (CALA, 1973;LOWE-MCCONNELL, 1987;ARGUMEDO, 2005) which were recorded specimens with lengths greater than 1 m. On average, the silver arowana in the lake has length and weight higher than in other basins in Peru, except in the Amazon basin, as reported by Duponchelle et al. (2012). In other sense, the length of first sexual maturity in silver arowana was determined in Peru as 62 cm for females, being the base for regional regulations of minimum capture size (TANG; GOMEZ, 2005). In another study, the length of first sexual maturity in the Ucayali basin was 65.9 cm and 73.9 cm for females and males, respectively (AYALA, 2001), and in the river Caucaya-Colombia, it was determined 75 cm and 72 cm Production of baby arowana for females and males, respectively (SANCHEZ et al., A total of 14595 baby arowanas were extracted 2007). The differences may be due to the different from the lake, with a mortality level of 2.30% in the conditions of aquatic ecosystems and the fishing extraction-gathering process, remain viable and sold pressure, what is happening with the fertility too. It is to aquariums in Iquitos a total of 14260 baby important to consider these results in the establishment of arowanas. In this regard, management fishermen and rules for fishing in the area. Concerning to the spawning, gatherers made on the appeal did not cause it occurred in synchrony with the rising of water level significant losses in the number of offspring marketed. (AYALA, 2001;TANG;GOMEZ, 2005;RUIZ, 2011), The use of this species was conducted in the months of except the reported by SANCHEZ et al. (2007), where March and April. In March was reported an extraction spawning occurred at low water levels. Related to the of 12541 larvae with a mortality of 2.62%, remain sex ratio, the proportion determined as 1:1 show that the viable and sold 12 213 larvae. In April, 2054 larvae Manage Program established in the area is, possibly, were extracted with a mortality rate of 0.34%, retrieving the population (PRADA-PREDREROS; remain viable and sold 2047 larvae to aquariums in AGUILAR- GALINDO, 1997) and it is an indicator that Iquitos. It should be noted that the existence of relation the fishing has not destabilized the sex ratio (TRESIERRA; between the Putumayo regime and the fishing of the CULQUICHICON, 1993). Finally, this is the first report species, which high water level contributed well in that shows number of fingerlings extracted by fishing in reducing harvest levels in April (14.073%). It was also one of the main areas for capturing the species for observed that the offspring in stage I had a higher ornamental trade, being this activity very important for mortality rate (3.49%) in comparison to offspring in economic sustainability of the communities around the stage II (2.11%).