Composition, abundance and biomass of the benthic fish fauna from the Guaritico river of a Venezuelan floodplain

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Composition, abundance and biomass of the benthic fish fauna from

the Guaritico river of a Venezuelan floodplain

C . L a s s o1 J . C a s t r o v i e j o2 K e y w o r d s : Fish c o m p o s i t i o n , a b u n d a n c e , b i o m a s s , b e n t h i c fish, f l o o d p l a i n s y s t e m s , G u a r i t i c o R i v e r , V e n e z u e l a . T h e c o m p o s i t o n , a b u n d a n c e a n d b i o m a s s o f t h e b e n t h i c fish f a u n a w e r e s t u d i e d a l o n g a 6 k m s t r e t c h of t h e G u a r i t i c o R i v e r . T h i s w a t e r c o u r s e is l o c a t e d in t h e w e s t e r n p l a i n s o f V e n e z u e l a a n d b e l o n g s t o t h e A p u r e River f l o o d p l a i n s y s t e m . M o n t h l y c o l l e c t i o n s f r o m J u n e , 1990 t o J a n u a r y , 1991 w e r e m a d e b y m e a n s o f a s m a l l t r a w l i n g a p p a r a t u s r i g g e d t o d u g o u t c a n o e s a c c o r d i n g t o t h e d e s i g n o f L o p e z - R o j a s et a l . ( 1 9 8 4 ) . 42 fish species w e r e i d e n t i f i e d with a d o m i n a n c e of s p e c i e s f r o m t h e o r d e r s S i l u r i f o r m e s a n d G y m n o t i f o r m e s . T h e fish a s s e m b l a g e d i f f e r e d m a r k e d l y from o t h e r V e n e z u e l a n r i v e r s y s t e m s . S e a s o n a l l y , h i g h e r d i v e r s i t y a n d e v e n n e s s w e r e o b s e r v e d at t h e h i g h w a t e r p h a s e while t h e a b u n -d a n c e , r e l a t i v e b i o m a s s a n -d C P U E w e r e h i g h e r a t l o w w a t e r .

Composition, abondance et biomasse des poissons bentniques dans la rivière de plaine Guaritico du Venezuela M o t s clés : A b o n d a n c e , b i o m a s s e , p o i s s o n s b e n t h i q u e s , s y s t è m e d e p l a i n e d ' i n o n d a t i o n , rivière G u a r i t i c o , V e n e z u e l a .

L a c o m p o s i t i o n , l ' a b o n d a n c e et la b i o m a s s e d e la f a u n e p i s c i a i r e b e n t h i q u e o n t é t é é t u d i é e s s u r u n t r o n ç o n d e 6 k m d e la rivière G u a r i t i c o . C e s y s t è m e s e situe d a n s les p l a i n e s o c c i d e n t a l e s d u V e n e z u e l a et a p p a r t i e n t a u réseau h y d r o g r a -p h i q u e d e l a rivière A -p u r e . D e s r é c o l t e s m e n s u e l l e s d e j u i n 1990 à j a n v i e r 1991 o n t é t é f a i t e s à -p a r t i r d e -p i r o g u e s é q u i -p é e s d ' u n c h a l u t ( m o d è l e L o p e z - R o j a s et a l . 1984).

S u r les 4 2 e s p è c e s d e p o i s s o n s i d e n t i f i é e s p r é d o m i n e n t les S i l u r i f o r m e s e t G y m n o t i f o r m e s . L ' a s s o c i a t i o n p i s c i a i r e dif-fère n e t t e m e n t d e celle d e s a u t r e s s y s t è m e s d e rivière d u V e n e z u e l a . Les plus g r a n d e s d i v e r s i t é et é q u i t a b i l i t é ont é t é o b s e r v é e s p e n d a n t la p é r i o d e d e h a u t e s e a u x a l o r s q u e l ' a b o n d a n c e , la b i o m a s s e r e l a t i v e e t la c a p t u r e p a r u n i t é d ' e f f o r t ( C P U E ) é t a i e n t les p l u s f o r t e s e n p é r i o d e d ' é t i a g e .

1 . I n t r o d u c t i o n

T h e study of t h e fish c o m m u n i t i e s associated with the m a i n channel of Venezuelan rivers began in 1978 with the e x p e d i t i o n of t h e r e s e a r c h vessel « E a s t -w a r d » t o t h e L o -w e r O r i n o c o . T h e results revealed the presence of a fish f a u n a practically u n k n o w n u p t o that t i m e . D u r i n g t h e expedition, a trawling a p p a -ratus was designed t o sample in shallower areas. T h e results of t h e efficiency of t h i s gear were published by L ô p e z - R o j a s et a l . (1984). Similar collections

1. Asociacion Amigos de Donana, 2182, 41080 Sevilla, Espana & Museo Historia Natural La Salle, 1930, Caracas 101O-A, Venezuela.

2. Asociacion Amigos de Donana, 2182, 41080 Sevilla, Espana.

were c a r r i e d o u t in t h e N a p o River ( E c u a d o r ) b e t -ween 1981-1983 (Stewart et al. 1987). C o l l e c t i o n s were later m a d e in t h e O r i n o c o River D e l t a using e x p e r i m e n t a l t r a w l i n g nets (Cervigon 1982, 1985, Cervigon & N o v o a 1988, N o v o a 1 9 8 2 , 1 9 8 6 , N o v o a & C e r v i g o n 1982, P o n t e 1990, R a m o s et a l . 1982). S y s t e m a t i c research o n t h e taxonomic, ecological a n d fishery aspects of t h e b e n t h i c fish f a u n a of t h e A p u r e River began in 1983 (Castillo 1988, M a c h a d o -Allison 1987, M a r r e r o 1984, 1990, P r o v e n z a n o & Castillo 1984, P r o v e n z a n o et al. 1984 a, b , c). T h i s p a p e r r e p o r t s t h e results of t h e research c a r r i e d o u t in t h e G u a r i t i c o River ( A p u r e River basin). In 1989, the river w a s d e c l a r e d a part of a specially p r o t e c -ted wildlife a r e a . T h e objectives of our r e s e a r c h were : 1) t o determine the species composition of t h e

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72

C. LASSO, J. CASTROVIEJO

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fish f a u n a associated with t h e b o t t o m o f t h e river

i n o r d e r t o m a k e c o m p a r i s o n s with o t h e r similar

systems ; 2) t o quantify the a b u n d a n c e , b i o m a s s ,

a n d catch per unit effort ( C P U E ) determined for the

first t i m e by means of the a p p a r a t u s designed by

L ô p e z - R o j a s et al. (1984).

2 . S t u d y a r e a

The study was m a d e on the last 6 km stretch of

the Guaritico River (locally known as c a n o G u a r i

-tico) before its confluence with the Apure River (Fig,

1). The Guaritico River is located on the upper

sec-t i o n of sec-the A p u r e River Basin (Ramia 1972) in a

Fig. 1. Study area (dots indicate the studied river section).

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region of seasonally flooded savannas (Scharger &

Gonzalez 1973, W e l c o m m e 1979). T h e climatology

of the area shows t w o contrasting periods ; the dry

season, which extends from N o v e m b e r to April a n d

the rainy season, which extends from May to

Octo-ber. These climatic conditions lead to two

hydro-metric periods : low waters (December-May) a n d

high waters (June-November) (Fig. 2). In this study,

collections of fish were m a d e during b o t h periods.

<

J F M A M J J A S O N D

Fig. 2 . Water level variations of the Guaritico River (1990). Fig. 2 . Variations du niveau de l'eau de la rivière Guaritico ( 1990).

During 1990, m e a n monthly air t e m p e r a t u r e ranged

between 25.1 ° C (July) a n d 28.9 ° C (April). T h e

Guaritico River supports a seasonally inundated

gal-lery forest. T h e m o s t representative tree species are

Nectandria pichurini ( H . B . K . ) Mez. a n d Dugnetia

riberensis Arist. O n the river side next to the

gal-lery forest, there is also a t r e e c o m m u n i t y k n o w n

locally as « mangle », d o m i n a t e d by Coccoloba

obtusifolia Jacq. (Castroviejo & Lopez 1985).

According to Sioli's classification o f A m a z o n i a n

river waters, the Guaritico River shows clear-waters

characterized by a smaller concentration of

suspen-ded solids and a higher water transparency t h a n

white-waters. Ranges for p H , water t e m p e r a t u r e ,

and conductivity were : 6.0-7.8 p H units ; 28-32 ° C ;

a n d 19.4-21.9 ^ S . c m

- 1

, respectively. W a t e r

trans-parency (Secchi) showed seasonal oscillations during

the year a n d was generally higher near t h e c o n

-fluence of the Guaritico with the Apure River. Water

t r a n s p a r e n c y was 25 cm at the end of t h e dry

sea-son a n d 20 cm at the beginning of the rainy s e a s o n .

T h e b o t t o m of the channel showed the t w o types o f

clays (grey and red) described by Marrero (1990) for

t h e A p u r e River.

3 . M a t e r i a l s a n d M e t h o d s

Monthly collections were made during the high a n d

low water periods between June 1990 a n d J a n u a r y

1991. Collections were made with a trawling fishing

apparatus adapted to dugout canoes according to the

design made by Lôpez-Rojas et al. (1984). Each

traw-ling lasted for 10 min, covering a mean distance of 147

m . , at depths ranging from 2-10 m (Table 1). Catches

were preserved with formaldehyde in the field. At the

laboratory, fishes were identified, weighed and

mea-sured. Species abundance was estimated with respect

to the total fishes caught monthly. Diversity ( H ' ) was

calculated by the Shannon-Weaver index (1949) a n d

the evenness (V*) was determined as the inverse value

of H* max. Species biomass was calculated as the

per-centage in weight with respect to the total fish caught

a n d also in terms of k g . h a

- 1

. The latter value a n d

density (ind. ha~ ') refer to the area covered by a 10

min trawling effort. The C P U E is expressed as

k g . h a . h o u r ~

4. R e s u l t s

4.1. Fish species

42 species from 5 orders, 13 families and 38 genera

were identified (Table 2). W i t h 26 spp (61 °7o) t h e

Siluriformes were the best represented g r o u p ,

fol-lowed by the Gymnotiformes (11 spp., 26.2 % ) , a n d

by the Rajiformes, Perciformes, a n d P l e u r o n e c t i

-formes which together represented 12 % (5 s p p . ) o f

the identified species (Table 3). The dominant

families were t h e Loricariidae, Pimelodidae, a n d A p t e

-ronotidae with 10,9 a n d 7 species, respectively. F o u r

t a x a were identified only to t h e generic level

(Pota-moirygon s p . , Hemiancislrus s p . , Duopalatinus s p . ,

a n d Rhamphichthys s p . ) . A new genus a n d species

from the family Loricariidae was recorded ( P r o v e n

-z a n o F . , pers. c o m m . ) as well as a new species from

t h e genus Porotergus (Apteronotidae).

Aphanotu-rulus frankei (Loricariidae) represents a new record

for the Venezuelan fish fauna. Before o u r r e p o r t ,

this species was k n o w n only from the Ucayali River

Basin in P e r u .

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74 C . LASSO, J. CASTROVIEJO

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Table 1. Total number of trawls, effective trawls a n d time of trawling .Period : June. 1990 - January, 1991. Tableau 1. Nombre total de chaluts, chaluts efficaces, et durée de chalutage. Période : juin 1990 - janvier 1991. M O N T H S J U N E JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER JANUARY N u m b e r of trawls 13 9 18 12 12 18 11 9 N u m b e r of efective

trawls 12 9 18 II 11 16 11 8 t total trawls

(minutes) 120 90 180 110 110 160 110 80

Table 2. List of fish species associated with the bottom of the Guaritico River. Tableau 2. Liste d'espèces de poissons benthiques de la rivière GuanrJco. R A J I F O R M E S

P O T A M O T R Y G O N I D A E

01 Potamotrygon orbignyi (Castelnau) 1885 02 Potamotrygon sp.

S I L U R I F O R M E S A G E N E I O S I D A E

03 Ageneiosus brevififis Cuvier & Valenciennes 1840 04 Ageneiosus ucayalensis Castelnau 1855 C E T O P S I D A E

05 Cetopsis coecutiens (Lichtenstein) 1819 D O R A D I D A E

06 Leptodoras Imne/li Eigenmann 1940 07 Megalodoras irwini Eigemann 1925 08 Pterodoras apurensis (Fernandez- Yépe/r 1965 H Y P O P H T H A L M I D A E

09 Hypophlhalmus edematus Spi\ 1829 L O R I C A R I I D A E

10 Aphanoiorulus Jrankei Isbrucker y Nijssen 1985 11 Hemiancistrus sp.

12 Limatutivhthys punctatus (Regan) 1904 13 Loricaria cataphmcta Linnaeus 1758 14 Loricarichthys niaculatus (Bloch) 1794 15 Panaque nigroimeutus (Peters) 1877 16 Pseudohemioduri luticepts (.Regan) 1904 17 Pterygoplichthys ntultirrudiatus (Hancock) 1824 18 Sturisoma rosirarumes (Spi.x) 1829 19 Loricariidae ncn. et sp. nov. P I M E L O D I D A E

20 Callophysus mucrupterus (Lichtenstein) 1819 21 Duopatatmus *p.

22 Hemisorubirn platyrhynchos (Cuvier & Valenciennes) 189(1 23 Pimelodidae gen. et sp. nov.

24 Pimelodelta gracilis (Cuvier & Valenciennes) 1890 25 Pimetodus blochii Valenciennes 1840 26 Pimetodus altissimus Eigenmann & Pearson 1942 27 Pinirampus pinirampu (Spix) 1829

28 Pseudoplatystoma fasciatum (Linnaeus) 1766 GYMNOT1FORMES

APTERONOTIDAE

29 Adontosternarchus devenanzii Mago-Leccia, Litndber y Baskin. 1985

30 Adontosternarchus sachsi (Peters) 1877 31 Apieronotus bonapartii (Castelnau) 1855 32 Porotergus sp. nov.

33 Sternarchoxiton porcinum Eigenmann & Allen 1842 *4 Siernarchorhamphus muelteri (Steindachner) IH81 35 Sternurchorhynchus curvirosrris (Boulenger) 1877 R H A M P H 1 C H T H Y I D A E

36 Rhamphichthys s p . STERNOPYGIDAE

37 Distocyctus conirostris Eigenman & Allen 1942 39 Rhabdolichops eatswardi Lùndberg & Mago-Leccia, 1985 PERCIFORMES

C I C H L I D A E

40 Geophagus altifrons Heckel 1840 SCIAENIDAE

41 Plagtoscion squamostssimus (Heckel) 1840 SOLFIDAE

42 Hypociinemus mentalis (Gùnther) 1862

Table 3. Families, genera, and species for each of the orders trom the Guantico River. Tableau Nombres de familles, de genres et d'espèces de chaque ordre de la rivière Guaritico.

O R D E R FAMILIES GENERA SPECIES/ORDER %

R A J I F O R M E S 1 1 2 4,8 S I L U R I F O R M E S 6 24 26 61,9 G Y M N O T I F O R M F S 3 10 11 26,2 P E R C I F O R M E S 2 2 2 4,8 P L E U R O N E C T I F O R M E S 1 1 1 2,4 T O T A L 13 38 42 100

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4 . 2 .

Diversity a n d a b u n d a n c e

Highest diversity values were recorded between

June and September with a m a x i m u m in August

(Fig. 3). Diversity decreased between October a n d

J a n u a r y with lowest values in December. Species

richness values were highest in J u n e (21 ssp.) a n d

lowest in January (13 ssp.). Evenness showed a simi­

lar trend to diversity. Highest equity values were

recorded in August while lowest values were recor­

ded in December.

Considering the collections for the enure sampling

period, the Siluriformes was the most a b u n d a n t

order (53.3 9b) followed by the G y m n o t i f o r m e s

(44.7 % ) . The remaining orders represented only

2 9o. Except in O c t o b e r a n d November, the Siluri­

formes was the dominant group throughout the sam­

pling period. In December, this g r o u p represented

almost 100 9b of the catches (Fig. 4). Except for the

Gymnotiformes, the c o n t r i b u t i o n of the other

groups was small. In J u n e , however, a b u n d a n c e of

the Perciformes reached 20 9b. Figures 5 a-c show

the monthly relative a b u n d a n c e of each species.

MINT!

(vi

jun Jul Aug Sap Oct Nov Dac Jan

Fig. 3. Variations of fish diversity ( H ' ) and evenness. Fig. 3. Vaiiations de la diversité (H') et de l'équitabilité pisciaires.

RELATIVE ABUNDANCE (%)

1 0 0 t 9 0 8 0 7 0 5 0

50

40

30

20

1 0

0

i

U T

• RAJIFORMES • S I L U R I F O R M E S 0 GYMNOTIFORMES B P E R C I F O R M E S EU PLEURONECT1FORMES

J U N J U L AUG SEP OCT NOV DEC J A N T O T A L

Fig. 4. Monthly relative abundance of each fish order. Fig. 4. Abondance mensuelle relative des 5 ordres de poissons.

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76 C . LASSO, J. CASTROVIEJO (6) JUr€, 1 9 9 8 SP8 s p l 2 Spl4 s p l 8 5P22 sp27 sp32 sp34 sp37 sp39 SP41 SP9 SP13 SP16 SP19 SP21 SP29 SP33 SP35 SP38 SP4B flUQUST, 1998 Sp4 s p l 0 s p l 3 s p l 8 Sp23 sp25 Sp27 S p 3 1 sp34 sp39 sp7 SP12 3pl6 3p21 sp24 sp26 sp29 3p32 sp38 sp41

I A B U N D A N C E {%)

IWEIGHT(%)

Fig. 5 a. Relative abundance and biomass of fish species for June-August, 1990 (codes on Table 2). Fig. 5 a. Abondance relative et biomasse des différentes espèces de poissons en juin-août 1990 (code-chiffres : tableau 2).

J u n e was the only m o n t h in which the m o s t a b u n -d a n t species (Plagioscion squamossisimus, 17.8 % ) did n o t belong to t h e Siluriformes or G y m n o t i f o r -mes. This species was followed by Hypophthalmus

edentatus (12.2 °/o). In July, Pimelodus blochii s h o

-wed a 20.4 °7q a b u n d a n c e follo-wed by

Sternarchorhamphus muelleri with 13.6 % . In August, a b u n

-dance was similar a m o n g species except for

Loricaria cataphracta a n d Duopalatinus sp. which d o m i

-nated with 17.7 % and 15.2 % , respectively. P.

blo-chii was again the most a b u n d a n t species (35.7 % )

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SEPTEMBER, 1998

s p 5 S P 6 Sp8 5P13 SP14 SP16 SP18 s p l 9 SP21 SP22 sp25 Sp26 SP28 sp38

OCTOBER. 1990

SP13 SP14 SP18 S P 1 9 SP21 S P 2 5 Sp26 S P 2 9 S P 3 8 S P 3 2 S P 3 8 s p 3 9 sp41

NOVEMBER. 1998

Sp6 S P 1 3 Spl4 S P 1 8 Sp21 S P 2 5 s p 2 6 5 P 2 7 S P 2 9 Sp38 Sp34 s p 3 7 s p 3 8 S P 3 9 Sp41

• A B U N D A N C E ^ ) ^ W E I G H T ( % )

Fig. 5 b . Relative abundance a n d biomass of fish species for September-November, 1990 (codes on Table 2 ) . Fig. 5 b . Abondance relative et biomasse des différentes espèces de poissons en septembre-octobre 1990 (code-chiffres : tableau 2).

(18.4 °7o). In O c t o b e r , a G y m n o t i f o r m

(Eigenman-nia macrops) showed highest abundance values (24.9

% ) for the first t i m e . This species was followed b y

L. cataphracta (23.4 % ) . The Gymnotiformes clearly

dominated in November {Rhabdolichops eastwards

28.6 % ; E. macrops, 24.9 °7o). In December, L .

cataphracta a n d P. blochii showed again highest

a b u n d a n c e (60.8 % for b o t h species). Finally, in

J a n u a r y , P. blochii was again dominant (32.7 % ) .

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7 8 C. LASSO, J . CASTROVIEJO (8)

1 0 0

s p l s > 2 s o l 4 SP18 SP19 S P 2 1 S P 2 5 S P 2 6 S P 3 8 seAl 5 P 4 2

• ABUNDANCE(%) ^WEIGHT(%)

Fig. 5 c. Relative abundance a n d biomass of fish species for December (1990)-January (1991) (codes on Table 2). Fig. 5 c. A b o n d a n c e relative et biomasse des espèces de poissons en décembre 1990-janvier 1991 (code-chiffres : tableau 2).

In t e r m s of i n d . h a ~ lowest values were recor-d e recor-d b e t w e e n J u n e a n recor-d S e p t e m b e r with m i n i m u m v a l u e s in A u g u s t (115 i n d . h a-1) - H i g h e s t

(0

1 0 0 0 . C

"b

s e e

ç

c

2 0 0

4)

a

0

values were recorded between October a n d J a n u a r y ( m a x i m u m of 870 ind. h a-1 in December (Fig. 6).

Fig. 6. Monthly fish abundance variations (ind. ha ' ) . Fig. 6 . V a r i a t i o n s m e n s u e l l e s d ' a b o n d a n c e pisciaire ( i n d . h a- 1)

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-B E N T H I C FISH FAUNA F R O M T H E GUAR1TICO R I V E R

4

. 3 .

Biomass and C P U I

W i t h respect lo the total catch, the relative bio­

mass indicated a d o m i n a n c e of the Siluriformes

(64.9 % ) followed by t h e Rajiformes (21.5 °7o), and

Gymnotiformes (12.9 °?o). T h e Perciformes and the

Pleuronectiformes together indicated biomass values

< 1 % . During the 8 m o n t h s sampling p e r i o d , bio­

mass of the Siluriformes was the highest during 6

m o n t h s (65 % ) . Only in N o v e m b e r a n d J a n u a r y ,

was this g r o u p displaced by the G y m n o t i f o r m e s

(52.9 % ) and by the Rajiformes (85.1 <7o), respecti­

vely (Fig. 7). T h e relative b i o m a s s values for each

species are shown in Figures 5 a-c. In J u n e t h e rela­

tive b i o m a s s v a l u e for Pimetodus altissimus was

24.2 % while a new genus a n d species (Loricariidae)

had a value of 17.4 °/o. In J u l y - A u g u s t ,

Megalodo-ras irwini had t h e highest b i o m a s s values (36.6 %

a n d 82.8 % . respectively). Only in S e p t e m b e r , did

we observe highest a b u n d a n c e values corresponding

to highest b i o m a s s values for one species (P. blo­

chii, relative b i o m a s s - 42.9 °/o). In O c t o b e r , L.

cataphracta was first (32.3 °7o) followed by E.

macrops (32.5 °?o). In N o v e m b e r , a G y m n o t i f o r m

(Sternarchorhamphus muelleri) showed the highest

biomass values (3.0 % ) . P. blochii (44.7 % ) a n d

Stu-risoma rostrata (24.3 °7o) represented t h e most

important species in December. Highest b i o m a s s of

the Rajiformes (81.3 % ) was observed in J a n u a r y

for t h e first time.

In terms of k g . h a

- 1

, t h e lowest biomass value

was recorded in J u n e (1.7 k g . h a ' ) • '

n

July-August, biomass increased slightly to 9.6 k g . h a ~

1

and then decreased in September-November. Hig­

hest values were observed in D e c e m b e r - J a n u a r y

(26.3 k g . h a - 1 in January) (Fig. 8). The C P U E sho­

wed a similar pattern t o biomass. Lowest values cor­

responded to J u n e (10.6 k g . h a

- 1

) a n d highest

values to J a n u a r y (164.4 k g . h a

-

•). (Fig. 9).

5 . D i s c u s s i o n

Most of the species from the Guaritico River

belong to t h e O r d e r s Siluriformes and G y m n o t i f o r ­

mes (88.1 % ) . This situation contrasts with records

from other neotropical freshwater ecosystems cha­

racterized by the d o m i n a n c e of characoid fishes

RELATIVE BIOMASS (%)

1 0 0

T • R A J I F O R M E S • SILURIFORNES E2 GYMNOTIFORMES

B

PERCIFORMES

D PLEURONECTlFORtvtS

J U N J U L A U G S E P OCT NOV CEC J A N TOTAL

Fig. 7. Monthly variations of the relative biomass of Fish order. Fig. 7. Variations mensuelles de la biomasse relative des 5 ordres de poissons.

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80

C . L A S S O , J. CASTROVIEJO

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ta

2 8 2 4 O>20 JE

1 6 (0 1 2 CD 1 2

m

8

E

8

o

4

m

a

N

Fig.

Fig. 8. Monthly fish biomass variations ( k g . h a- 1) . . Variations mensuelles de la biomasse de poisson (Kg. h a- 1) .

ta

1 8 8 • C 1 6 0 O) 1 4 0 _ 1 2 0 UJ 1 9 8 1 3 8 0

a.

6 0

O

40 2 0 0 ,

.S

N

Fig. 9. C P U E variations ( k g . h a . h1) .

Fig. 9. Variations de la capture par unité d'effort : C P U E ( K g . h a . h- 1) .

( L o w e - M c C o n n e l 1975, 1987 ; Lowe-McConnell &

H o w e s 1981). Similar results have been reported for

t h e b e n t h i c fish c o m m u n i t i e s of the A p u r e River

( P r o v e n z a n o & Castillo 1984 ; P r o v e n z a n o et al.

1984 a, b , c) a n d of t h e Orinoco River Delta

(Lôpez-R o j a s et al. 1984 ; (Lôpez-R a m o s et al. 1982). In the lower

O r i n o c o River, L ô p e z - R o j a s et al. (1984) distinguis­

h e d t w o fish assemblages ; o n e assemblage in t h e

deepest sections of t h e m a i n channel d o m i n a t e d by

G y m n o t i f o r m e s , a n d a n o t h e r o n e in adjacent shal­

lower a r e a s d o m i n a t e d by high richness of

chara-coid fishes. In the G u a r i t i c o River, however,

cha-racoids specially the « p i r a n h a s » (Pygocentrus a n d

Serrasalmus) represent accessory species. Their pre­

sence in o u r catches m a y be considered accidental

as they were caught in the net while preying on other

fishes.

In spite of the absence of complete fish lists, we

c o m p a r e d the preliminary fish inventories of ben­

thic species of the Guaritico a n d Apure rivers a n d

o f the O r i n o c o Delta. This comparison revealed a

higher similarity between the Apure and the Guari­

tico River. T h e basic difference between these two

rivers was the absence of certain genera in the Gua­

ritico River : Aspredinidae (Xyliphius), Cetopsidae

(Pseudocetopsis), Pimelodidae {Megalonema,

Pime-lodina, Platysilurus, Pseudopimelodus), Loricarii­

dae (Apistofohcaha, Denteclus, Farioweila,

Lamontichthys, Paraloricaria, Spatutoricaria). A p t e r o n o

-tidae (Sternarchella, plus two new genera) (Proven­

z a n o F . , pers. c o m m . ) . T h e presence of o t h e r spe­

cies from the Rajiformes, Clupeiformes,

Percifor-mes, a n d Pleuronectiformes recorded by us in

t h e Guaritico River and not yet recorded from the

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B E N T H I C FISH FAUNA F R O M T H E G U A R I T I C O RIVER

81

Table 4. Accompanying fish species found during the trawling

of the bottom of the Guaritico River.

Tableau 4. Espèces de poissons accompagnants trouvées pendant le chai ut age du fond d e la rivière Guaritico. C L U P E I F O R M E S

C L U P E I D A E

Pellona Jlavipinnis (Valenciennes) 1839 C H A R A C I F O R M E S

A N O S T O M I D A E

Leporinus fasciatus (Bloch) 1794 C H A R A C I D A E

Acestrocephalus sp. Galeocharax gulo (Cope) 1870 Knodus breviceps (Eigenmann) 1908 Mylossoma duriventris (Cuvier) 1818 Pygocentrus caribe (Valenciennes) 1849 Roeboides a/finis (Gunther) 1868 Serrasalmus alîuvei Ramirez 1965 Serrasalmus irrilans Peters 1877 Serrasalmus medinai Ramirez 1965 C U R I M A T I D A E

Curimata sp.

Steindachnerina argenlea (Gill) 1858 Steindachnerina s p .

H E M IO D O N T I D A E

Hemiodus unimaculatus (Bloch) 1794

A p u r e River, is m o s t p r o b a b l y due t o t h e absence

of m o r e conclusive fish inventories t h a n t o the

absence of these orders in the latter. W i t h regard

to the benthic fish fauna of the Orinoco River

(exclu-ding typically e s t u a r i n e species), some g e n e r a are

found in this region which have not yet been

recor-ded from the Guaritico River : Engraulidae

(Ancho-vict, Lycengraulis), A s p r e d i n i d a e (Hoplomyzon,

Platystacus), D o r a d i d a e (Opsodoras), Pimelodidae

(Nannorhanmdia, Perugia), H y p o p o m i d a e

(Steato-genys), Soleidae ( A p i o n i c h t h y s ) .

T h e difference in the n u m b e r of fish species from

different rivers has been related t o the size of the

d r a i n a g e surface a n d length of the main river c h a n

-nel (Welcomme 1985). This observation m a y explain

the lower a b s o l u t e n u m b e r of fish species (alpha

diversity according to Lowe-McConnell 1987)

recor-ded from the G u a r i t i c o River in comparison to the

A p u r e River and t h e O r i n o c o Delta (Table 5). T h e

lower number of fish species from t h e Guaritico m a y

also be the result of t h e smaller transects sampled

by us (some 6 km) c o m p a r e d to t h e transects

sampled in the A p u r e River a n d Orinoco Delta. A n o

-ther factor t o consider in explaining the diversity

a n d distribution o f fish species of the G u a r i t i c o

River is the type of w a t e r . T h e clear w a t e r s of

this river differ from t h e white waters of t h e A p u r e

a n d O r i n o c o rivers. The importance of water

types on the distribution a n d diversity of n e o t r o

-pical fishes has previously been discussed (Weitzman

& W e i t z m a n 1982). In the A p u r e River, the type

of s u b s t r a t u m has also been linked to the

distribu-t i o n of some Siluriform and Gymnodistribu-tiform fish

spe-cies (Provenzano & Castillo 1984, P r o v e n z a n o et al.

1984 a, b , c). In o u r study, the available d a t a d o

not allow us to consider yet any possible

relations-hips between the type of s u b s t r a t a and fish species.

In the Guaritico River, diversity a n d evenness

sho-wed a similar temporal p a t t e r n . Highest values were

observed at high waters rather t h a n low w a t e r s . A

g r o u p of fish species was observed d u r i n g b o t h

periods (Table 6) a n d a t least 10 species of catfishes

(Siluriformes) were collected exclusively at high

waters. These species may be migrating f r o m the

A p u r e River into the Guaritico River.

Table 5. Comparison a m o n g the number of fish species from each order from the Guaritico River, Apure and Orinoco River Delta. Tableau 5. Comparaison des nombres d'espèces de chaque o r d r e dans les rivières Guaritico et Apure et dans le delta de l ' O r é n o q u e .

RIVERS G U A R I T I C O A P U R E O R I N O C O D E L T A O R D E R S ssp. ssp. (%) spp.

m

R A J I F O R M E S 2 4.8

_

_

S I L U R I F O R M E S 26 61,9 54 71,0 25 42,4 G Y M N O T I F O R M E S 11 26,2 22 29,0 25 42,4 P E R C I F O R M E S 2 4,8 3 5,1 P L E U R O N E C T I F O R M E S 1 2,4 1 1.7 O T H E R S 5 8,4 (Clupeiformes a n d Characiformes) T O T A L 42 100 76 - 59 100

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82 C. LASSO, J. CASTROVIEJO

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Table 6. Presence and size range (mm) of the species collected in the Guaritico River. Measurement1; for the Gymnotiformes = total length ; for the Rajiformes - discal width ; other orders = standard length.

T a b l e a u 6. Présence et taille moyenne (mm) des espèces récoltées dans la rivière Guaritico. Mensurations pour les Gymnotiformes -longueur totale ; p o u r les Rajiformes = largeur du disque ; autres ordres - -longueur stardard.

SIZE RANGES (mm)

SPECIES JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER JANUARY

Potamotrygon orbignyi 122-125 Potamotrygon sp. 330-430 Ageneiosus brevifilis 37-63 A. ucayatensis 43-59 108 Cetopsis coecutiens 36-39 37 Leplodoras tinnelli 120-146 145 Megaloàoras irwmi 430 400-540 185-271 Pterodoras apurensL 65 66 53 Hypophlhalmus edentatus 36-38 71-100 Aphanotorulus frankei 115 59-155 Hemiancislrus sp. 79-81 Ltmatulichthys punclatus 28-84 114-128 114-145 128 Loricaha cataphracta 62-69 48-81 72-188 88-224 56-124 75-191 80-210 Loricarichthys maculatus 56 118-190 98-114 102 63-162 164-181 Panaque nigrotineatus 260 Pseudohemiodon laliceps 33-34 48-75 60-61 45-92 P. mttltirradialus 119 Sturisoma rostralum 223 88-86 159 75-113 184-227 108-235 176-214

New genus and species 162-166 71-177 123-127 101-182

Catiophysus macropterus 83

Duopalatinus sp. 29 51-150 56-145 165 141-190 142-196 124-159

Hemisorubim platyrhynchos 130 132

New genus and species 164 42-129

Pimelodella gracilis 54-62 52-64 43-74 72-40 52-73 55-57 Pimetodus altissimus 112-127 120-135 53-156 Pimetodus blochii 72-45 77-133 53-156 56-75 62-122 62-135 66-137 Pintrampus pinirampu 62-67 49-248 61-200 Pseudoplalystoma fasciatum 250 A. devenanzi 138 64-121 83-84 115-124 92-111 A. sachsi 93-147 93-139 Apteronotus bonapartit 54-318 279 Porotergus sp. n. 179-218 236-260 69-164 56-93 Slernarchogiton poreinum 88 S. muelleri 104-390 150-253 146-349 S. curvirostn 270 Rhamphichthys sp. 324 Distoctclus coniroslris 223 261 283 285-299 Eigenmannia macrops 205-229 155-244 75-184 96-264 48-259 90-264 75-216 86-120 Rhabdolichops catswardi 180-280 174-243 56-217 57-205 105 Geophagus altifrons 25 Plagioscion squamosstsimus 35-39 62-66 125 105-194 16 Hypoclinemus mentalis 62-80 45-50

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BENT HIC FISH F A U N A FROM T H E G U A R I T I C O RIVER

83

T h e overall fish a b u n d a n c e was higher at low

water a n d lower at high watei A similar trend has

been reported for G y m n o t i f o r m a n d L o n c a r i i d a e

fishes from the A p u r e River ( P r o v e n z a n o F . , u n p u

-blished). During the dry season, water level a n d

cur-rent a r e r e d u c e d . At t h e onset ol the rams a n d the

s u b s e q u e n t increase in water level, water depth a n d

water current a r e increased. These conditions m a y

explain the smallei fish a b u n d a n c e . In our case,

however, t h e smallest fish density was recorded at

low water ( J a n u a r y ) . H o w e v e r , b i o m a s s values

during this m o n t h w e t e highest due to t h e presence

of Rajiform fishe.s (low a b u n d a n c e a n d high

b i o m a s s ) .

Similar to r e p o r t s for the O r i n o c o River Delta

( L ô p e z - R o j a s et al. 1984), we did not find a clear

relationship between t h e C P U E and other variables

(time of collections, lengths of trawling distances,

d e p t h of trawlings, type of s u b s t r a t a ) . T h e r e w a s

however, a relationship between the C P U F a n d t h e

period of the year. Highest C P U F valuer were

recor-d e recor-d at low water. Collections ol fishes in the

Gtia-ritico River with the same fishm,. &eu! ranged b>n

ween 1-130 individuals p e r trawi. In r!u. O r i n o c o

Delta, the n u m b e r of fishes caught per trawl was

always higher t h a n 100. This i n f o r m a t i o n is

indica-tive of t h e high a b u n d a n c e and fish b i o m a s s found

in the O r i n o c o Delta with respect t o the G u a r i t i c o

River. T h e selectivity of the fishing a p p a r a t u s ,

favouring the catch of smaller fishes, was observed

in our work where we caught specimens r a n g i n g

from 33 m m to 540 m m s t a n d a r d length

(Megalo-doras irwini) and 430 m m discal width

(Potamotry-gon sp.) (Table 6). T h e b o t t o m of the G u a r i t i c o

River showed an assemblage of fish species in

dif-ferent developmental stages ; species which inhabit

the b o t t o m for a period of their life-cycles (i.e.

ben-thonic y o u n g stages of Siluriforms) or which

inhabit the b o t t o m t h r o u g h most of their d e v e l o p m e n

-tal stages (Table 7).

C o m p a r i n g our d a t a with the information p r o v i

-ded by M a c h a d o - A l l i s o n (1987) a n d by P e n c z a k &

Lasso (1991), the highest b i o m a s s value (26.3 Kg.

ha ' ) recorded for the Guaritico River is low c o m

-pared t o mean values for other tropical freshwater

river systemps.

A c k n o w l e d g e m e n t ! !

We Vkish IO thank the A s o c i a c i ô n A m i g o s de D o nana for the partial funding of this protect and O Castillo ( F O N A I A P ) , C . A . Invega. Fun-d a c i ô n La Salle Fun-de C i e n a .is Naiurales, anFun-d members of the family Mal-dortado for their logistic support ; X. Etguezàbal, H . Pinango and B. Mora (M A . R . N . R . ) for their valuable assistance in t h e field work. W e specially thank E . Vâsquez for hK critical reading and for his English translation. W. Wilbert helped us in the editing o f the English version. In a d d i t i o n we recognize A . Rial, R. Perez and V. P o n t e for their c o n t r i b u t i o n in the production of the graphs ; H . L ô p e z - R o j a s . A . Machado- Allison and F . P r o v e n z a n o (Universidad Central d e Venezuela) who provided

valua-s and finally we thank M. Garcia for her typing o f the papier.

Table 7. Species and m o n t h of collection of juvenile stages associated with the b o t t o m of t h e Guaritico River. Tableau 7. Espèces et mois de capture des stades jeunes récoltés sur le fond de la rivière Guaritico.

MONTHS JUNE JULY AUGUST SEPTEMBER

A. brevifilis X A. ucayalensis X C. coecutiens X X P. apurensis X X X H. edentatus X X A. frankei P. laticeps X X C. macropterus X Duopalatinus sp X X P. altissimus X P blochii X P. fasciatum X P. pinirampu X G. altifrons X P. squamossisimus X X

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84 C . L A S S O , J . CASTROVIEJO

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