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Studies on f Neotropical Fauna and Environment

Beitrage zur neotropischen Fauna

Editorial Board: W. E. Ankel Giessen and Santa Marta L. Brundin Stockholm W. Bücherl Sao Paulo E. du Bois- Reymond Marcus Sao Paulo J. Gery Saint-Genles (Dordogne) J. lllies Schlitz E. F. Kilian Giessen and Valdivia H. W. ·Koepcke Hamburg P. W. Wygodzinsky New York

Editor-in-chlef: J. lllies Schlitz

PUBLISHED BY SWETS & ZEITLINGEÁ B.V. • AMSTERDAM Studies on Neotropical Fauna and Environment 12 (1977), pp. 217-223.

Breading Season, Sexual Rate and Fecundity of Basilichthys australis Eigenmann 1927, from Maipo River, Chile. (Atherinidae, Pisces)

Carlos A. MORENO, Roberto URZÚA and Nibaldo BAHAMONDE

Valdivia and Santiago ( received 31 March 1976)

INTRODUCTION

The Chilian autochthonous freshwater fish most harvested is the "pejerrey"', Basilichthys australis Eigenmann 1927, (Duarte et al., 1971). Nevertheless, there is no basic information dealing with its life history, which would permit a better management of this resource. The only research carried out in Chile dealing directly with resource management of freshwater fishes has been done in Galaxiid species (Campos 1970 a; 1972) and in the "argentine pejerrey", Basilichthys bonaeriensis Cuv. & Val. (Burbidge et al., 1974). B. australis inhabits rivers, small brooks, ponds and lakes between Aconcagua river in the north and Rahue river in the south (Fowler, 1945). lt is a pelagic species (Campos, 1970 b) with omnivorous feeding habits, that consumes mainly diatoms, filamentous algae and both larvas and adult specimens of Chironomidae (Urztla et al., 1975f The present study deals with sorne aspects of its spawning, e.g. breading season, sexual rate and fecundity.

11. MATERIAL ANO METHODS

1630 specimens were obtained, collected r'nonthly between August 1969 and August 1970 a:t Maipo river (Santiago, Chile) near Llolleo with a nylon gill net of 18 mm stretched mesh that was dragged along from tbe extremes by two men from one shore to the other for two hours. Total length was measured to the nearest millimetre, total weight to the nearest gram and gonad weight to the nearest 0.1 g. Sex was identified visually in mature specimens and, by means of smears under optic microscope in small fish and immature ones. The gonad­ somatic relation (G.S.R.) was determined foreach individual and then the mean for each month was calculated with the formula: G.S.R.=Wgx 100/ wt 218 C. A. MORENO ET AL. where Wg = gonad weight (g) and Wt = total weight (g) without considering gonad weight. Relative fecundity was determined in a subsample of JO females during the breading season. For each female the total number of eggs was counted under a binocular microscope (24x). An egg subsample of four females was used for measuring the egg diameter overa graduated slide (0.01 mm). Condition (K) was determined for each individual and then the mean was calculated in each sex monthly by the formula: K= Wt/ Lt3 x 10.000 where Wt = total weight (g) and Lt = Total length (mm) (Lagler, 1966). In each month the percentage of empty stomachs was determined.

III. RESULTS ANO DISCUSSION

A. Breading season. The gonad somatic relation indicates the proportion in percentage that the gonad weight acquires in relation to body weight and represents in a indirect way sexual mature states in a fish population (Hureau, 1970). Fig. J shows monthly obtained values in both sexes. Female values are slighlty higher than male values, although both curves tend to be similar. Maximum values of G.S.R. for both sexes appear in August and descend abruptly up to November. According with Hureau (1970) and Angell (1973) this descent corresponds to the breading season in which gamete evacuation occurs.

99 t t-+ 1' + crcr

0,9 0

e 5 0,85 X 'ci w vi o,eo ~ (!) hJ 0 ,75 t5 I-- 0,70 0 z o 0 ,65 U

ASON DJ FMAMJ J 1969 1970

Fig. 1. Monthly average of gonad-somatic relation (left) and condition index (right) of Basilichthys austro/is Eigenmann from Maipo river. ON CHILEAN BASILICHTHYS AUS.TRALIS 219

For considering G.S.R. averages, the curve represents general spawning tendencies. Mature specimens can be captured between March and April but are insignificant in the population under analysis. The smaller female with mature gonads presented a total length of 176 mm and was captured in August 1970.

Condition (K) increases from 0.69 in December to 0.87 in March (Fig. !), the smallest K values coincide with the minor G.S.R. values. This correlation indicates that G.S.R. is a good index so as to stablish spawning time in this population. It is known that in fishes the minor K values appear immediately after spawning (Lagler, 1966). Nevertheless, empty stomachs that appear at that time (Table 1) can influence the descent of K values.

Table 1. Empty stomach percentages in monthly samples of Basilichthys austro/is Eigenmann of Maipo river.

Month Percentage Month Percentage August 7.0 February O.O September 6.3 March O.O October 5.8 April O.O November 27.0 May O.O December 79.0 June 3.0 January 32.0 July 19.3

B. Sex ratio. The number of female specimens is higher than males (P< 0.05) (Table 2). Nevertheless the monthly sex ratio points out that in the sample place, females are present in a significant way only during November, December and January (P<0.05). Increase of female number can be explained hypothetically by a differential sex migration, where males migrate first and female later. This migration could occur during summer when the river current increases caused by snow melting of the Central Andes of Chile. This also increases turbidity and the river seems to be of chocolate (Fuenzalida 1966). What emphasizes the hypothesis of a migration towards the sea, escaping from this turbidity is that during February the captured specimens declined, although the capture effort was similar. B. austro/is as other chilean atherinids are recent in the continental waters (McDowall, 1971) and it seems that physiologically it can support the marine environment.

C. Fecundity. Relative fecundity of B. austro/is mature females, whose total length ranges between 176 mm and 242 mm fluctuates between 1,418 and 7,531 eggs, following a relation of relative fecundity (F) v / s total length (L) of F = 0.0001 LJ m 220 C. A. MORENO ET AL.

Table 2. Sex ratio in mothly samples of Basilichthys australis F.igenmann, collected at Maipo river between August 1969 and August 1970.

Number Percentage Sexratio Month female male female male / August (1969) 32 39 45.1 54.9 0.82 September 64 38 62.7 37.3 1.68 October 51 34 60.0 40.0 1.50 November 65 30 (!) 68.4 31.6 2. 16 December 130 53 (!) 71.0 29.0 2.45 J anuary ( 1970) 82 42 (!) 66.1 33.9 1.95 February 19 IO 65.5 34.5 1.90 March 86 107 44.6 55.4 0.80 April 77 101 43.3 56.7 0.76 May 97 92 51.3 48.7 1.05 June 97 94 50.8 49.2 1.03 July 51 43 54.3 45.7 1.18 August 54 42 56.3 43.8 l.28 TOTAL 905 725 (!) 55.5 44.5 1.25 (!) Significant difference (P<0.05) Chi-square test.

with a correlation of O. 72 with a significance up to 5% (Fig. 2). In ten analyzed specimens the right gonad presents a greater number of eggs. Average number of eggs. Average number of eggs in the right gonad was 2,269 and in the left one 1,787.

In the majority of fishes the number of eggs at first gradually increases with age, and then as the individual approaches senilíty, it usually begins to decrease (Nikolsky, 1963). In the analyzed population, although the females of greater size were included, a tendency towards stabilization in the number of eggs is not observed. This fact shows a virtual absence of adult specimens probably dueto its intensive harvest. Egg diameter ranges between 0.2 and 2.4 mm with a bimodal frequency distribution. Probably. the greater size mode is evacuated as in Galax ias maculatus (Jenyns) and the minor size mode reabsorbed (Campos, 1970 a). A similar fact can happen in Cilus montii Delfín according to Miranda (1975). The percentage of the total eggs of the subsample that belongs to the greater size mode was studied by means of graphic analysis in probability paper (Cassie, 1954), a method that permits to remove the bimodal curve from its constituent curves (fig. 3). The removed groupes are: the first one with an average of O. 7 mm diameter (S D = O. 76) and the second one of 1.8 mm (SD = 0.62). The total amount of released eggs can be calculated in a 32% of the relative fecundity, assuming that both size groups of eggs present the same proportion in the sub­ sample then in the whole.Jemale population. ON CHILEAN BASILICHTHYS AUSTRALIS 221

F• 0,0001 L3.277 r • O, 719 ( P( 0,05) 8 n• 10 -LL 7 -e,) 'O e o e e,) :, o ~ s -e e,) 4 01 01 l;• 3

~ .o• 2 E z:,

180 200 240 210 TOTAL LENGTH (mm.)

Fig. 2. Relative fecundity and total length relation in Basilichthys austro/is from Maipo river. ( IO mature fema le considered).

2 .5 ii

2.0

É 1.5 5. e 1.0 0 :¡;.. ~ 0.5 "'

Fig. 3. Diameter of the eggs of Basilich1hys aus1ralis Eigenmann. Accumulative percentage of frequency drawn in probability paper. 222 C. A. MO RENO ET AL.

Acknowledgements. We thank sincerely Dr. Hugo Campos for his great help in data analysis and also Dr. Ed uardo del Solar for his helpful comments.

SUMMARY

Breading season, sexual rate, fecundity and minimum size for reproduction was studied in Basilichthys austro/is Eigenmann 1927. Monthly samples were collected with a gill net from a river of the central part of Chile. It was found that the spawning period lasts from August to November, the smaller mature female had 176 mm T. L. Sorne changes in the sexual rate suggest a migration to the sea during summer time; the relative fecundity kept a relation of F = 0.000 I L3 27• However, according to the diameter of the eggs these would only have a viability of 32%.

RESUMEN

En base a muestras mensuales de pejerrey de río (Basilichthys austro/is). recolec­ tados en el río Maipo, se ha determinado su época de desove, relación de sexos y ·su fecundidad relativa. Encontrandose que la mayor parte de esta población desova entre Agosto y Noviembre, que la talla miníma de desove es de 176 mm. y que la fecundidad relativa sigue una relación F = 0.000 I L3 27, sin embargo los huevos viables sólo corresponden al 32%. La existencia de una posible migra­ ción al mar en verano de esta especie, relacionada con cambios en la relación de sexos y el aumento de la turbiedad en_e l rio es discutida.

REFERENC ES

Angell, C. L. (1973). Algunos aspectos de la biología de la lisa. Mugí/ curema Valenciennes, en aguas hipersalinas del Nororiente de Venezuela. Mem. Soc. Cien. Nat. La Salle 33. 223-238. Burbidge, R. G., Carrasco, M.C. and P. A. Brown ( 1974). Age,growth, length-weight relationship, sex ratio and food ha bits of tbe Argentine pejerrey, Basilichrhys bonariensis(Cuv. & Val.), from Lake Peñuelas, Valparaiso, Chile. J . Fish Biol. 6. 299-305. Campos, H. ( 1970 a). Galaxias maculatus (Jenyns) en Chile, con especial referencia a su reproduc­ ción. Bol. Mus. Nac. Hist. Nat. (Chile). 31. 5-20. (1970 b). Introducción de especies exóticas v su relación con los peces de agua dulce de Chile. Not. Men. Mus. Nac. Hist. Nat. (Chile) 14 (162), 3-9. ( 1972). Breeding season and early development of Brachygalaxias bullocky (Osteisch­ thves. Galaxiidae). Texas J . Sci. 23, 513-522. Cassie, R. M. ( 1945). Some uses of probability paper in the analysis of size frequency distribution. Aust. J. Freshw. Res. 5, 513-522. Duarte, W., Feito, R. Jara, C., Moreno, C. and A. Orellana ( 1971). lctiofauna del sistema hidro­ gráfico del río Maipo. Bol. Mus. Nac. Hist. Nat. (Chile) 32, 227-268. Fowler, H. W. (1945). Fishes of Chile. Systematic catalog. Part 2. Rev. Chil. Hist. Nat. 46, 22-57. Fuenzalida, H. ( 1966). Hidrografia. In Geografía Economica de Chile. Edición CO RFO. Sant iago de Chile. Hureau, J. C. (1970). Biologie comparée de quelques poissons a ntarctiques (Nototheniidae). Bull. lnst. océanogr. Monaco. 68 ( 139 1), 1-244. ON CHILEAN BASILICHTHYS AUSTRALIS 223

Lagler, K. F. ( 1966). Freshwater fishery biology. W. M.C. Brown Publishers. Dubuque. Iowa. McDowell, R. M. ( 1971). The galaxiid fishes of South America. Zoo!. J. Lin. Soc. 50 (1), 33-73. Miranda, O. B. ( 1975). Nota sobre la fecundidad aparente de la corvina (Cilus montii Delfin). Rev. Biol. mar. 15 (2), 201-206. Nikolsky, G. V. ( 1963). The ecology of Fishes. London, Academic Press. Urzúa, R., Karmy, E., Dlaz, C. and C. A. Moreno. (1975). Hábitos alimentarios del pejerrey del río Maipo (Basilichthys austro/is Eigenmann). Manuscript.

Address of the principal author: Instituto de Ecologia. Universidad Austral de Chile casilla 57-D. Valdivia. Chile. STUDIES ON THE NEOTROPICAL FAUNA

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