BIOLOQIUAL NOTES ON A FISH FROM BRAZIL 206

14. Biological Notes on a Fish from Brazil in the Society’s Aquarium. By SUNDER LAL HORA, U.Sc., P.R.S.E., P.Z.S., Zoological Survey of India, Calcutta.

(Offered for Publication by permission of the Director, Zoological Survey of India.)

[Read October 20, 1931.1

During a visit to the Aquarium of the Zoological Society of London towards tht. end of August 1931 I noticed an exhibit of two specimens of a Loricariid fish, 1al)elled Plecostomus commersoni. The Loricariidz are mostly found in the fast - running waters of South America, where they stick to rocks by means of their characteristic inferior sucker-like mouth. It has been assumed that when thrsc finhes fasten themselves to stones by means of the sucker-like mouth the respiration is then effected “ by taking in water through the gill-openings and expelling it again by the same passage in a reverse direction ” *. I haw observed, however, that in the torrent-inhabiting fishes of India?, such as Ctarra, Glyptothoraz, Pseudecheneis, and Balitora, the respiration takes placc in the normal way-the rhythmical suction of water into the oral cavity and its consequent expulsion through the gill-openings. Though Pseudechentis, and to a certain extent GZyptothorax, possess the type of suctorial mouth so charakristic of the Loricariidae, it was d a c u l t to say, in the absence of any observations on the living specimens, whether the method of respiration in the Loricariidae is normal or of the type assumed from the position of its mouth and the structure of its lips. In order to settle this point I decided to make observations on the two specimens in the Society’s Aquarium.

At my request the specimens in the Aquarium were placed a t my disposal by Mr. E. G. Boulenger, Director of the Aquarium, for making observations, and for this my best thanks are due to him. He also provided me with thc necessary apparatus and allowed me the use of the small laboratory in the Aquarium. The observations detailed below were made on the 15th and 16th September, 1931. The morphological details were sttudied later in specimciis preserved in the British Museum (Natural History).

I have to point out that the specimens in the Aquarium belong to the genus Loricaria, and not to Plecostomus It was not possible to identify them speci- fically, as the specific distinctions could not be studied in the living specimens.

As indicated above, my special object was to study the method of respira- tion, and for this purpose the following simple apparatus was designed. A mirror of a sufficiently large size (12”x 15”) was placed on a working table. On two opposite sides of the mirror two bricks were placed. A rectangular piece of glass was then placed on the bricks covering the mirror below. On this glass a rectangular dish was kept. At the time of making observations the fish were transferred to the dish. (The dish selected should be smaller than the distance between the two bricks, SO that every part of the dish can be reflected in the mirror below.)

Regan, Trans. Zool. Soc. London, xvu. p. 191 (1904). t Hora, Rec. Ind. MUR. xxv. pp, 591-596 (1923),

206 DR. SUNDER LAL HORA : BIOLOGICAL NOTES ON A

When placcd in the dish the fishes adhered to the bottom, so that their mouths and associated parts could be watched in the mirror. For making observations on the respiration of the fish a solution of carmine powder in water was used. A small cloud of this solution was floated quit,e close to and partly h low the snout of the fish, and it was then noticed that the fish inhaled the red particles of carmine through the mouth, and a stream of the solution was sccn coming out through the gill-openings. This showed that the respiration is effected in the normal way in Loricaria. A cloud of carmine kept near the gill- opening was not inhaled, but gradually drifted away from the fish. When the head of the fish was pressed against the substratum by hand the respiratory movements of the mouth stopped altogether. Even in these circumstances water was not taken in through the gill-openings. The full details of t h r observations made are as follows :-

When transferred to the dish the fish lay quietly a t the bottom and breathed hurriedly for a short time, but after a few minutes the respiratory movements slowed down and became apparently normal. It was then observed that as the fish lay closely applied to the substratum a gentle current of water was sucked in through the mouth and passed out of the gill-openings. This normal mode of breathing was so gentle that somewhat larger particles of the carmine powder near the mouth were hardly disturbed from their positions. The circular opening of the mouth was guarded by a velum-like membrane that could be stretched across i t to close i t entirely. Under normal conditions of respiration only a small portion of the membrane a t the anterior end appeared to be moved backwards and forwards, and through the narrow passage thus formed water was sucked in. The movements of the membrane could be easily watched and counted from above, as the reflected Iight from the mirror showed through the roof of the buccal cavity when the membrane was moved to and fro. Of thr two specimens cne was more active and behaved differently from the other. After every two or three normal breaths i t took in a deep breath, which was marked by the raising of the dorsal fin and the tail and also by a slight quivering movement of the posterior rays of the paired fins. Normally i t took about ninety-two breaths in a minute, of which about thirty were deep breaths. When the fish was touched with some object i t did not move off, but showed its excitement by taking in large gulps of water. When the head of the fish was pressed against the substratum it stretched the membrane across the mouth and stopped breathing altogether, without showing any marked uneasiness ; but soon after the pressure was released, after a minute or two, the fish darted quickly to another part of the dish, almost “ panting.” In nature the fish probably suspends respiration to tide over heavy floods.

The gill-opening shows some interesting modifications, and can be dividcd into two parts both morphologically as we11 as physiologically. It is small and extends obliquely in front of the base of the pectoral fin. In the part of the opening above the base of the fin the operculum is not provided with a loose membranous flap a t its posterior end, and fits very closely against the bones of the pectoral girdle. I have observed that this portion of the gill-opening takes no part in the respiratory movements of the fish. The remaining portion of the opening below the base of the pectoral fin is guarded by a broad flap of skin, and the clouds of carmine were exhaled through this part alone. The opening leads to a deep cavity in which the gills are situated.

In the case of the Indian hill-stream fishes i t was observed that only a small upper part of the gill-opening functioned in the respiratory movements of the fish, whereas the lower part was either non-functional or was opened only at the timc of a deep breath. In Loricaria eFactly the reverse of this has taken place,

FISH FROM BRAZIL IY THE SOCIETY’S AQUARIUM. 207

This is probably due to the method of fixation and progression in the two types of fishes. In Balitora, for instance, the pectoral fins are horizontally inserted and a number of the outer rays are closely applied to the substratum. In these circumstances the lower part of the gill-opening cannot function. In Loricaria, on the other hand, i t was observed that the paired fins were held obliquely, with the distal part of the anteriormost ray touching the substratiim. The carmine solution shot out through the gill-opening passed underneath the pectoral fin.

There can hardly be any doubt that in Loricaria the attachment to the sub- stratum is effected by the lips and the spines of the pectoral, ventral, and anal fins. A fish as i t lay at the bottom was held by the tail and moved forwards and backwards. It offered no resistance, but when I wanted to lift i t vertically upwards it became restless and loosened its hold on the substratum. I am therefore unable to say whether the lips form a definite sucker or not. Under normal conditions, when breathing goes on, the lips cannot form a vacuum sucker, and fixation is then effected through adpression. The spinous papille on the lips and the prickles on the fin-spines, which are directed posteriorly, enable the fish to hold fast to the substratum. The fish crawls along the substratum by using its paired fins alternately and by holding to the substratum with the lips.

I was informed by Mr. Vinall, Overseer of the Aquarium, that the two specimens now in the Aquarium formed part of a lot of four specimens presented to the Zoological Society of London by Mr. L. W. Hawkins on 8th January, 1931. Of these one died on 27th June and another on 25th August. I was further informed that these fishes are fed thrice a week on Daphnia or scrapped heart. As in running water such a food would be an impossibility, I wanted to observe them feeding. The two specimens were transferred to the dish, and a meal of Daphnia was provided for them. Although the small crustaceans kicked about under the snout of the fish, no excitement whatsoever was shown by the fish. In nature I believe these fish feed on algal slime which they scrape off the rocks, or on small insect larvs that stick on the rocks in fast currents. In the Aquarium I presume they would pick up food particles settled a t the bottom by accidentally rolling over them. The eyes being small and dorso- lateral in position could not assist in bottom-feeding, and the mouth being small and inferior could not be uscd for surface or mid-water feeding

The plates on the ventral surface of the body also help in fixation.

P. Z . S . 1932. P O W E R PI. I .

3

I . L.VENTRALIS V E N J f ? A L / S I 2 L.PUMIt-A PNMILA. 3 L. G[lTTItPALiS.

i? Z.S. 1932 P O W E R PI:II.

3.

I. _L_DAMARANA. 2 L PUMJLA CAFFER. 3 L VENTRALIS KARROOICA.