N SUKUMARAN and M N KUTTY Fisheries College, Tamil Nadu Agricultural University, Tuticorin

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1 Proc. ndian Acad. Sci., Vol. 88 B, Part, Number 5, October 1969, pp printed in ndia. Oxygen consumption and nitrogen excretion in mullet, Rhinomugil corsula (Hamilton), with special reference to swimming speed N SUKUMARAN and M N KUTTY Fisheries College, Tamil Nadu Agricultural University, Tuticorin MS received 27 April 1978 Abstract. An attempt is made to study the c, xygen consumption, COs output and the nitrogen excretion of the freshwater mullet Rhinomugil corsula. t is found that whereas the O consumption, the COs output and the respiratory quotient decreased with increase in the duration of exercise, the NH~-N and total-n excretion showed the opposite trend. Keywords. Oxygen consumption; nitrogen excretion; freshwater mullet; carbondioxide output. 1. ntroduction The relation of oxygen consumption to activity has been studied extensively (Spoor 1946; Wohlschlag 1957; Beamish 1970; Brett 1964, 1965; Smit and others 1965) and these results can be used to determine the level of metabolism only on the assumption that energy is derived exclusively from aerobic sources. Although anaerobic metabolism in fish forced to swim has not been investigated (Brett 1965 ; Kutty 1968, 1969, 1972 ; Beamish 1968 ; Smit et al 1971 ; Webb 1971 ; Karup pannan 1972) Kutty (1968) studied the changes of respiratory quotient (RQ)* in relation to swimming speed and duration of exercise in goldfish and rainbow trout. Kutty (1972) and Karuppannan (1972) studied the RQ and ammonia excretion in Tilapia mossambica exercised for hours together, and observed that while anaerobic energy utilisation was higtl during the initiation of exercise, protein utilisation increased with the increase in the duration of exercise. The object of the present study has been to find out the extent of anaerobic metabolism in the fresh water mullet, Rhinomugil corsula, exercised continuously for 5 hr at various swimruing speeds. An attempt to judge the extent of protein utilisation and relation of NHa-N and total-n excretion in exercised fish has also been made. i *RQ ~--- COl Output (vol)/oi consumed (vol) 345 '.~)--4

2 346 N Sukumaran and M N Kutty 2. Materials and methods The freshwater mullet, R. corsula, ranging from 15"7 to 20" 3 cm body length and from 32" 5 to 56"7 g body weight, were acclimated to 30 :k 0" 5 C in glass tanks. The fish were fed on a formulated diet containing rice-bran and groundnut oil cake in the ratio of 2 : 1 (Narayanan 1974). The experiments were done at the acclimation temperature. The experiments were performed in Blaka's respirometer (Blaka et al 1960; Smit 1965) made on transparent acrylic plastic, perspex. n the apparatus the risk were forced to swim against the water current created by a propeller, attached to an electric motor. By regulating the speed of the motor the water inside the swimruing chamber is recirculated at different current speeds. Four different swimming speeds were chosen for the present study, namely, 20, 38, 61 and 77 cm/sec. The fish acclimated at the test temperature was starved for 24 hr (Beamish 1964; Brett 1964) prior to the experiments. t was then kept for 12 hr in the respirometer to eliminate the handling effect. The swimming chamber was partly covered by a black plastic curtain to safeguard the fish from external disturbances. The fish medium used in this study was decarbonated water (Karuppannan 1972; Kutty and Peer Mohamed 1975; Narayanan 1974) which enabled the accurate carbon dioxide measurement. The fish was trained to swim for a few minutes immediately after introducing it into the swimming chamber. Most of the fish tested took easily to swimming in the chamber. The determination of O3 was done by unmodified Winkler method (APHA 1965). 25 ml of the samples were used for analysis. The total carbon dioxide was analysed by Maros-Schulek technique as modified by Kutty et al n this method 50 ml of the samples were used for analysis and this method proved adequate for accurate measurement of total carbon dioxide in water. Samples were analysed for ammonia following the method described by Kutty (1972), which is in general agreement with Stroganov (1962) and APHA (1965). 50 ml of the samples were distilled and nesslerised and ammonia contents were determined by Spectronic-20 at a wavelength of 420 m~. Total-N in water was measured by micro KjeldaJal method. 25 ml of the samples were digested with digestion mixture and 5 ml of concentrated sulplauric acid and subsequently determined the total-n using micro-kjeldahl apparatus. 3. Results The consolidated data are presented in table 1 and the plots of oxygen consumption, CO output and RQ against swimming speed are shown in figure 1; the closed circles are the values of the first hour (short-time exercise) readings and the open circles are the 5th kr (long-time exercise) readings. The rate of NH3-N and total-n excretion, quotients of NHs-N excretion, percentage of NH3-N in total-n are plotted against swimming speed in figure 2. From figure 1 it is evident that both the O3 consumption and COs output decrease with the duration of exercise as observed earlier in other teleosts (Brett 1964; Smit 1965 ; Kutty 1968 ; Karuppamtan 1972). Oxygen consumption increases with swimming speed at

3 O~ consumption and N~ excretion in mullet 347 Z 66~5 ',1 666 o< o ~.~ 0,~ ~ &6~ ~ O. ~ o~,~ ~ 0.,~ o q r~ t~

4 348 N Sukumaran and M N Kutty cj 1 'r ~ O.~ O Or- -- V hr C hr 300 g oo tj t. 400.C g 300 C O ~2oo ~ r E /) g u 1 i, Swimming speed (crn/sec) Figure 1. The rate of oxygen consumption and carbon dioxide output and respiratory quotient (RQ) in relation to swimming speed and duration of exercise in R. corsula, acclimated and tested at 30 C. all the 3 hr tested. The increase in the CO~ output with speed is maximum in the first hour and less in the fifth hour of exercise. Figure 2 displays data on NHa-N and total-n excretion ammonia quotient (AQ)*, nitrogen quotient (NQ**) and the percentage of NH3-N in total-n excretion for R. corsula exercised for 5 hr continuously. As opposed to the trends in 02 Gonsumption and COs output the N-excretion increased with the duration of exercise, as shown earlier by Kutty (1972) and Karuppannan (1972) in Tilapia *AQ ~--- NH3-N excretion (wt)/o~ consumed (wt) **NQ-~-Total-N excretion (wt)/o= consumed (wt)

5 03 consumption and N~ excretion in mullet 80.c_ 'hr 70 ~ 60 o 2 OE 1 c.g 349 V h r Q V hr AQ NQ! AG ~mlrnt Vhr B, ~ oc ~50 20 i i 60 Swimming speed (cmlsec) Figure 2. The rate of NHa-N and total-n excretion, ammonia quotient (AQ), nitrogen quotient (NQ) and percentage of NH3-N in total-n excreted, in relation to swimming speed and duration of exercise in R. corsula, acclimated and tested at 30 C. The inset shows the relation of nitrogen excreted to oxygen consumed in three different ratios, namely (a) atomic relation of N-excretion/O= consumed, (b) NHa excreted (Wt)/O= consumed (Wt) and (c) NHa excreted (Vol)/O= consumed (Vol). mossambica. NHa-N and total-n excretion also showed a sharp increase with increase in swimming speed for all the 3 hr tested. The percentage of NH3-N in total-n excreted, tends to remain constaat with increase of swimming spe ;d and duration of exercise. 4. Discussion t has been observed that energy utilisation, as measured from 02 consumption alone, increases in general with increase in swimming speed. n spite of eve~t precaution to maintain fish under least excitement, the 0,. consumption of fish measured at a single level of activity shows a wide range, probably duo to excitement

6 350 N Sukumaran and M N Kutty (Brett 1964 ;Smit 1965; Kutty 1968 ; Smit et a11971). The excitement may well be because of the stimulation of anaerobic metabolism, in view of the high RQ observed during the first hour of the exercise period. However, it should he pointed out that oxygen uptake during the first hour is also higher, so that both aerobic and anaerobic metabolism are initially higher possibly due to excitement. This excitement apparently decreases with increase in the duration of exercise. Brett (1964) found that there is considerable anaerobic energy utilisation, as judged from measuremeats of oxygen debt, in sockeye salmon swimming at high speeds. Kutty (1968) found that during sustained swimming at 20 C in fully saturated water, the mean RQ during the first hour of exercise amounted to 1 "66, and during hour~ 3-12 it stabilised at about 0"95. The anaerobic energy utilisation is less in R. corstt[a during the first hour of exercise, as compared with goldfish (Kutty 1968) and T. mossambica (Karuppamlan 1972), the RQ value (1 "24) of R. corsula du.ring the first hour of sustained swimming being lower. The long term RQ's on the other hand are below unity and values are close to protein-fat value, but it could not be fully separated from the anaerobic fraction. Kutty (1968), however, suggested more of protein or fat utilisation in goldfish forced to swim for long time at high speeds. Kutty's (1972) preliminary experiments showed that T. mossambica swam for 6 hr at single speed and Karuppannan's (1972) study on locomotory metabolism on T. mossambica confirmed that there is considerable involvement of protein metabolism during lortg term swimming. NHa-N and total-n excretion increase with swimming speed when R. corsula is exercised (both short term and long term), but in long term exercise the increase is sharp. This is mainly because the protein utilisation is more during long term exercise at sustained swimming speeds. The quotients also increase with both increase of speed and duration el exercise. n the highest speed tested, the AQ (vol relation) value increases from 0"11 to 0"25 with the increase of duration of exercise and they are very clo~e to the values observed in T. mossambica (Karuppannan 1972). Kutty (1972) found that the AQ value goes up to 0 "4 during the 6th kr of swimming in T. mossambica. n R. corsula, it is evident that AQ value increases 2-} times during the 5th hr of exercise, suggesting that proteins are a major so,tree of energy during long-term exercise. n this discussion it will be assumed that ammonia produced denotes energy derived fully from protein metabolism. However, anaerobic production of ammonia can occur especially in cases where the AQ goe~ above the clea~" aerobic maximum value of 0.27 suggested by Kutty (1972). This vak~e based on mammalian energetics is possibly art underestimate and a value above 0"3 can be expected in fish as discussed in Kutty (1979). t has been farther suggested after observations of Maet and Garcia Romea (1964) and Garcia Romea and Motais (i966) that NHa released can be used to bt;ffer the acid produced dt~ring anaerobic metabolism and NHa + ion is subsequ.ently ex,hanged at the gills for sodium ions (Na+). The increase in ammonia production in fish may be a mechanism fox aci&ba-e balance and conservation of Na + ions. The total-n excretion also showed the same pattern of NHa-N excretion, but the non-ammonia fraction showed slight increase witlt the increase of dtlration of exercise. The actual extent of involvement of this fraction (non-ammonia) in energy utilisation and acid-base regulation, if any, is difficult to be e~,timate,,t precisely from the data available. This aspect of the study can be elaborated fa~ther.

7 02 consumption and N2 excretion in mullet 351 References Anon 1965 Standard methods for the examination of water and waste water, 12th ed (New York: Am. Pub. Health Assoc.) Beamish F W H 1964 Respiration of fishes with special emphasis on standard oxygen consumption.. nfluence of oxygen; Can. J. Zool Beamish F W H 1968 Glycogen and lactic acid concentrations in Atlantic cod (Gadus morhua) in relation to exercise; J. Fish. Res. Board Can Beamish F W H 1970 Oxygen consumption of 1,~.rge mouth bass, Micropterus salmoides, in relation to swimming speed and temperature; Can. J. Zool Blaka P, Volf M and Cepela M 1960 A new type of respirometer for the determination of the metabolism of the fish in an active state; Physiol. Bohemoslov Brett J R 1964 The respiratory metabolism and swimming performance of young sockeye salmon; J. Fish. Res. Board Can Brett J R 1965 The swimming energetics of salmon; Sci. Am Garcia Romen F and Motias R 1966 Mise en e'vidence de changes Na+/NH4 + che l'anguille d'eau douce; Comp. Biochem. Physiol Karuppannan N V 1972 Studies on locomotory metabolism of Tilapia mossambica (Peters); Ph.D. Thesis, Madurai University, Madurai Kutty M N 1968 Respiratory quotients-in goldfish and rainbow trout; J. Fish. Res. Board Can Kutty M N 1969 Oxygen consumption in the mullet, Lia macrolepis with special reference to swimming velocity; Mar. Biol Kutty M N 1972 Respiratory quotient and ammonia excretion in Tilapia mossambica; Mar. Biol Kutty M N1979 Energy metabolism in mullet invited contribution : Chapter in lbp synthesis volume on grey mullets' (London: Cambridge University Press) (in press) Kutty M N, Karuppannan N V, Narayanan M and Peer Mchamed M 1971 Maros-Schulek technique for measurement of carbon dioxide production in fish and respiratory quotient in Tilapia mossambica; J. Fish. Res. Board Can Kutty M N and Peer Mohamed M 1975 Metabolic adaptations of mullet, Rhinomugil corsula (Hamilton) with special reference to energy utilisation; Aquaculture Maet J and Garcia Romeu F 1964 n mechanism of sodium and chloride uptake by the gills of freshwater fish, Carassius auratus.. Evidence for NH4+/NA + and HCOa-/C- exchanges; J. Gen. Physiol Narayanan M 1974 Studies on the biology of the mullet, Rhinomugil corsula (Hamilton), Ph.D. Thesis, Madurai University, Madurai Smit H 1965 Some experiments on the oxygen consumption of goldfish (Carassius auratus) in relation to swimming speed; Can. J. Zool Smit H, Amelink-Koutstaal J M, Vijverberg J and Von Vaupel-klein 1971 Oxygen consumption and efficiency of swimming goldfish; Comp. Biochem. Physiol. A Spoor W A 1946 A quantitative study of the relationship between the activity and oxygen consumption of goldfish; Biol. Bull. Mar. Biol. Lab. Woods Hole Stroganov N S 1962 Methods for ammonia, determination used in studies on fish metabolism, ed. E N Pavolovskii in The techniques for the investigation of Fish Physiology d. Akad. Nauk S.S.S.R. Podossenskii per. Moscow, U.S.S.R. Translation from Russian by srael Programme for Sci. Transl. Jerusalem Webb P W 1971 The swimming energetics of trout. 1. Oxygen consumption and swimming efficiency; Biol. Bull. (Woods Hole, Mass.) Wohlschlag D E 1957 Differences in metabolism rates of migratory and resident freshwater forms of an Arctic white fish; Ecology