Daily Ration of Japanese Spanish Mackerel Scomberomorus Niphonius Larvae

FISHERIES SCIENCE 2001; 67: 238–245

Original Article

Daily ration of Japanese Spanish mackerel Scomberomorus niphonius larvae

J SHOJI,1,* T MAEHARA,2,a M AOYAMA,1 H FUJIMOTO,3 A IWAMOTO3 AND M TANAKA1

1Laboratory of Marine Stock-enhancement Biology, Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto 606-8502, 2Toyo Branch, Ehime Prefecture Chuyo Fisheries Experimental Station, Toyo, Ehime 799-1303, and 3Yashima Station, Japan Sea-farming Association, Takamatsu, Kagawa 761-0111, Japan

SUMMARY: Diel successive samplings of Japanese Spanish mackerel Scomberomorus niphonius larvae were conducted throughout 24 h both in the sea and in captivity in order to estimate their daily ration. Using the Elliott and Persson model, the instantaneous gastric evacuation rate was estimated from the depletion of stomach contents (% dry bodyweight) with time during the night for wild fish (3.0Ð11.5 mm standard length) and from starvation experiments for reared fish (8, 10, and 15 days after hatching (DAH)). Japanese Spanish mackerel is a daylight feeder and exhibited piscivorous habits from first feeding both in the sea and in captivity. Feeding activity peaked at dusk. The estimated daily ration for wild larvae were 111.1 and 127.2% in 1996 and 1997, respectively; and those for reared larvae ranged from 90.6 to 111.7% of dry bodyweight. Based on the estimated value of daily rations for reared fish, the total number of newly hatched red sea bream Pagrus major larvae preyed by a Japanese Spanish mackerel from first feeding (5 DAH) to beginning of juvenile stage (20 DAH) in captivity was calculated to be 1139Ð1404.

KEY WORDS: consumption, daily ration, feeding, gastric evacuation rate, Japanese Spanish mackerel, larvae, Scomberomorus niphonius, Seto Inland Sea.

INTRODUCTION However, for a long time, most studies had focused primarily on the biology of adult fish.3–6 Recently, Japanese Spanish mackerel Scomberomorus information on early life history has been niphonius is commonly distributed in south- accumulated and several peculiar ecological western Japan and is one of the important fisheries features have been clarified: precocious develop- resources particularly in the Seto Inland Sea. Total ment in the digestive system of the larvae,7 catch in the sea exceeded 6000 t in the mid 1980s, piscivorous habits from the first feeding stage,8 but has recently decreased to less than 500 t mainly brief larval occurrence synchronized with peak because of overfishing.1,2 It is hoped to recover abundance of their prey fish, rapid growth in early the decreased stock by fishing regulations and life stages,9 and diel changes in vertical distribu- releasing seedlings. tion and feeding rhythm.10 Because of the unique In order to stabilize the catch and to establish feeding habits of larvae (i.e. a consistent piscivory more effective fisheries management, it is neces- from first feeding) a sudden increase in Japanese sary to accumulate biological information and to Spanish mackerel biomass could have larger pre- elucidate the recruitment process of the species. dation impacts on coastal pelagic fish commu- nities than those of many other piscivorous fish *Corresponding author: Tel: 81-75-753-6225. Fax: 81-75-753- species whose feeding habits shift from plank- 6229. Email: [email protected] tivory to piscivory at a more advanced stage of life. aPresent address: Agricultural Administration and Fisheries Division, Uwajima Regional Office, Ehime Prefecture, Uwajima, Assessment of predation impacts on other fish is Ehime 798-0036, Japan. needed for future stock enhancement of this Received 16 May 2000. Accepted 23 October 2000. species. Daily ration of Japanese Spanish mackerel larvae 239

Although Japanese Spanish mackerel has also fecture Chuyo Fisheries Experimental Station) in been expected as a target species for sea-farming the Hiuchi-nada Sea, the central waters of the Seto because of its high growth potential [reaching Inland Sea (Fig. 1). A total of nine and 10 sets of 10 mm total length (TL) in a month and 600 mm TL larva-net tows were conducted with an interval of in the first growing season: May to November], 2–3 h from 11:37 h on 13 to 11:42 on 14 June 1996 sibling cannibalism in early life has constituted a and from 10:33 on 3 to 09:57 on 4 June 1997, major difficulty in mass production.11,12 By quanti- respectively. Details of the sampling method are fying their food consumption, an appropriate described in Shoji et al.10 Japanese Spanish mack- feeding schedule is indispensable for mass pro- erel larvae were sorted in the laboratory and stan- duction of this fierce fish in captivity. dard lengths (SL) were measured to the nearest This study is part of a larger project designed to 0.1 mm using a dissecting microscope. Stomach estimate the predatory impact that young Japanese contents of 143 (3.9–11.5 mm SL) and 209 (3.0– Spanish mackerel have on their piscine prey 10.3 mm SL) Japanese Spanish mackerel larvae populations. We estimated the daily ration of were examined for 1996 and 1997, respectively. Japanese Spanish mackerel larvae using the speci- Then the larval bodies and stomach contents were mens obtained from successive 24 h samplings in dried for 24 h at 60°C and the stomach contents the central waters of the Seto Inland Sea. Estimates weight index (I) was calculated as follows. of daily ration were compared with those under laboratory conditions. dry stomach contents weight I È ˘ 100 (1) = Í ˙ ¥ Î dry bodyweight ()W ˚ In order to detect growth in the early life stages MATERIALS AND METHODS of Japanese Spanish mackerel in the sea, we examined sagittal otoliths of sea-caught fish:9 early Field sampling larvae collected by periodical sampling using the larva-net in the surveyed area from May to July Two sets of a 24h survey were carried out during 1997 and late larvae and early juveniles collected in cruises of the R/V Hiuchi (Toyo Branch, Ehime Pre- June and July by the ‘Patchi-ami’, a boat seine

Fig. 1 Central area of the Seto Inland Sea showing sampling stations of Japanese Spanish mackerel larvae over a 24 h period on 13–14 June 1996 () and 3–4 June 1997 (). Rearing experiments were conducted in Japan Sea-farming Association (JASFA) Yashima Station () during May to June 1999. 240 FISHERIES SCIENCE J Shoji et al.

fishery which is operated primarily for Japanese where C is the consumption of food during the anchovy Engraulis japonica larvae and juveniles time interval from 0 to t, I0 and It are average I at in the Hiuchi-nada Sea. These fish collected in time 0 and t, and R is the instantaneous gastric 1997 for growth analysis were preserved in evacuation rate. 90% ethanol. In the laboratory, according to the The field study suggests that Japanese Spanish otolith increments validation, right-side sagittal mackerel larvae are daylight feeders.10 Assuming otoliths of 70 fish were removed under a dissecting there is no feeding from sunset to sunrise, R for the microscope and increments were counted for age sea-caught larvae can be estimated from the deple- determination.9 tion of I during the night. The evacuation rate is therefore given by

-Rt¢ IIesr= ss Sampling in captivity where R is calculated from the average Is of

Artificial fertilization was carried out with a pair the samples collected at sunset (Iss), at sunrise of adult Japanese Spanish mackerel captured in (Isr), and the time interval between sunset and a drift gill net in the Harima-nada Sea, the eastern sunrise (t¢). Seto Inland Sea in May 1999. Eggs were trans- The R for fish in captivity was estimated from ported to Yashima Station, Japan Sea-farming the depletion of I during the starvation experi- Association (JASFA; Fig. 1), Takamatsu, Kagawa, ments using the following equation: and maintained in 0.5 m3 tanks under natural light conditions. Water temperature ranged from RtII= ()(1 ln 0 t ) (3) 18.2 to 19.5°C during the experiments. The initial To calculate the daily amount of food consump- density of fish at the beginning of the experiments tion, estimated C for each time interval during was about 15/L. Newly hatched larvae of red 24 h under both wild and rearing condition were sea bream Pagrus major, which are usually used summed. Using daily ration estimates (%W) of the as prey in culturing Japanese Spanish mackerel, predator (S. niphonius) and dry bodyweight of prey were fed sufficiently from the first feeding (mean of 100 newly hatched red sea bream larvae: (5 days after hatching (DAH)).11,12 0.029 mg), the total number of red sea bream con- In order to estimate the gastric evacuation rate sumed by a Japanese Spanish mackerel from first of Japanese Spanish mackerel larvae, starvation feeding (5 DAH) to early juvenile stage (20 DAH) experiments were conducted at the age of 8, 10, was calculated. and 15 DAH with the mean fish size of 6.8, 8.7, and 12.1 mm SL, respectively. Because Japanese Spanish mackerel larvae are piscivorous and begin sibling cannibalism without piscine prey, 100 fish RESULTS were isolated from one another using 2 L plastic cups at the beginning of each starvation experi- Diet and stomach fullness in the sea ment. Then 10–15 fish were sampled at once with the interval of 0.5 or 1.0 h and Is were calculated. During both of the sampling periods in 1996 Evacuation rate was estimated using the depletion and 1997, the diets of Japanese Spanish mackerel of I up to 10 h from the onset of the starvation larvae consisted exclusively of fish larvae of other experiment. species (Fig. 2). Clupeiformes was the most A diel change in I was examined by sampling 31 dominant taxa, occupying more than half of the times in 24 h from 03:00 h to 03:00 h with an inter- stomach contents in number (53.8% in 1996; 51.5% val of 0.5 or 1.0 h on the same day as the starvation in 1997), followed by Gobiidae (7.7% in 1996; 21.6% experiments. Fifteen to 20 fish were sampled from in 1997). the tank for each I calculation. Diel changes in the percentage of empty stomachs and mean I were evident in both years (Fig. 3). Occurrence percentage of empty stomachs decreased during the day, reached a Estimation of gastric evacuation rate and minimum (3.2% in 1996; 0% in 1997) at dusk, and daily ration then consistently increased throughout the night to a maximum (83.3% in 1996; 63.7% in 1997) at The daily ration of Japanese Spanish mackerel was dawn. Diel changes of I showed an opposite trend estimated in terms of per cent bodyweight from the to that of the percentage of empty stomachs; a Elliott and Persson model:13 consistent decrease after dusk and increase after --Rt Rt C=-() It I0 e Rt()1- e (2) dawn. Daily ration of Japanese Spanish mackerel larvae 241

Fig. 2 Composition of stomach contents (percentage in number) of Japanese Spanish mackerel larvae collected during 24 h samplings in the central Seto Inland Sea on 13–14 June 1996 and 3–4 June 1997. Cl, Clupeiformes; Cb, chub mackerel; Go, Gobiidae; Ca, Callionymidae; Un, unidentiﬁed.

Fig. 4 Diel changes in estimated consumption (%W/hour; ) and accumulated consumption (%W; ) for Japanese Spanish mackerel larvae. Using the estimated gastric evacuation rate of 0.302 in 1996 and 0.338 in 1997, daily ration was calculated as 127.2%W and 111.1%W in 1996 and 1997, respectively.

for the sea-caught larvae in 1996 and 1997 was estimated as 0.302 and 0.338, respectively. The Is and estimated Rs were used to estimate the food consumption for each time interval (C). The estimated food consumption was high during the daytime with a peak at sunset (12.3% W/h in 1996; 16.6% W/h in 1997: Fig. 4). Daily ration, which was obtained by summing the amount of food consumption during each time interval, reached 127.2 and 111.1% W/day in 1996 and 1997, Fig. 3 Diel changes in percentage of empty stomachs respectively. () and stomach contents weight index (I; ) of Japanese Spanish mackerel larvae. Decline of I with time after sunset (h) was expressed as follows: I = 31.64exp Estimation of gastric evacuation rate and (-0.302h), R2 = 0.98 in 1996 and I = 29.02exp(-0.338h), daily ration for reared larvae R2 = 0.98 in 1997. In the starvation experiments in captivity, R was Estimation of gastric evacuation rate and derived from the set of I-values during 10 h since daily ration for the sea-caught larvae the onset of fasting which were plotted in the exponential equation. The R obtained from ﬁsh at 8, 10, Using the depletion of I during the night (Fig. 3) and 15 DAH were 0.282 (R2 = 0.95), 0.324 (R2 = 0.94), which was plotted in the exponential equation, R and 0.311 (R2 = 0.98), respectively. Time to 90% 242 FISHERIES SCIENCE J Shoji et al.

Table1 Instantaneous gastric evacuation rate, gut clearance time (time to 90% digestion of prey), and daily ration of Japanese Spanish mackerel larvae in the sea and in captivity Size range Instantaneous Gut clearance Daily ration (mm SL) evacuation rate time (h) (%W) Wild Year 1996 3.9–11.5 0.302 7.6 111.1 1997 3.0–10.3 0.338 6.8 127.2 Reared Age (day) 8 5.9–8.4 0.282 7.6 104.9 10 8.0–9.9 0.324 7.3 111.7 15 11.0–13.8 0.311 7.4 90.6

digestion of prey for the three ages was between 7.3 and 7.6 h which fell within the range of the wild fish: 6.8–7.6 h (Table 1). As shown in Fig. 5, diel changes in I of the reared Japanese Spanish mackerel larvae exhibited a similar trend to that of wild larvae; increased after dawn, peaked at about sunset, and decreased during the night. The daily rations for the reared fish reached 104.9, 111.7, and 90.6% W at 8, 10, and 15 DAH, respectively (Fig. 6; Table1). Using the highest (111.7% W) and lowest (90.6% W) daily ration estimates in captivity and mean dry bodyweight of the prey [i.e. newly hatched red sea bream larvae (0.029 mg], the total food consumption of a Japanese Spanish mackerel from the first feeding (5 DAH) to the beginning of juvenile period (20 DAH) was calculated as 1139–1404 prey Fig. 5 Diel changes in stomach contents weight index larva/predator. (I) of the reared Japanese Spanish mackerel larvae at 8, 10, and 15 days after hatching (DAH). Growth and development

Under the rearing condition, Japanese Spanish mackerel larvae initiated feeding at 5 DAH and transformation to juvenile was mostly completed by 20 DAH. Based on the age estimation from sagittal otoliths of the sea-caught fish in 1997, Japanese Spanish mackerel grew to about 20 mm SL in 20 DAH (Fig. 7). Body size of the reared fish at 20 DAH (18.7 ± 1.6 mm SL) was smaller than that of the wild fish (t-test, P < 0.01), but these two growth curves did not show a significant difference (ANCOVA, P > 0.05). Using the estimated values of daily ration (111.1% W for the wild fish in 1997 and 90.6–111.7% W for the reared fish) and dry bodyweight (W: in mg) derived from standard length (L: in mm) using the equation (Shoji J, unpubl. data, 1999): WL=¥¥2. 115 10-4 3. 587 (4) Fig. 6 Diel changes in accumulated food consumption (%W) for the reared Japanese Spanish mackerel larvae established for the laboratory-raised fish, the mean at 8, 10, and 15 days after hatching (DAH). Daily rations gross growth efficiency (total food consump- were calculated as 104.9, 111.7, and 90.6%W at 8, 10, and tion/dry bodyweight gain) of Japanese Spanish 15 DAH, respectively. mackerel from the first feeding to 20 DAH in the sea Daily ration of Japanese Spanish mackerel larvae 243

The R exponentially decreased with ambient temperature in piscivorous age-0 bluefish in captivity from 5 h at 30°C to 10 h at 20°C for 90% evacuation of the stomach contents.21 In our study, the water temperatures during the laboratory experiments (18.2–19.5°C) and the field samplings (16.2–21.5°C) were lower and fell within a relatively narrow range, which correspond to that observed during the short-term occurrence of wild larvae in the Seto Inland Sea.9,10,22 The R and daily ration of Japanese Spanish mackerel larvae would not fluctuate greatly under relatively small changes in water temperature in the period of their occurrence in the Seto Inland Sea. Yamashita and Bailey23 described the exponen- Fig. 7 Growth curve of wild Japanese Spanish mackerel tial change in rates of ingestion and gastric evacua- larvae and early juveniles collected in the central Seto tion of walleye pollock Theragra chalcogramma Inland Sea in 1997 (¥) and reared in 1999 (; mean of 10 larvae feeding on rotifers that were dependent fish each). upon the size of the larvae. They considered that decreased evacuation rates with increased larval size (and age) were associated with the development of the digestive system: midgut coiling which (in 1997) and in captivity was estimated as 33.4% begins at about 5.2 mm SL (13–16 DAH). The devel- and 26.0–32.1%, respectively. opmental change in R was not distinct in Japanese Spanish mackerel (Table1). This would be due to the precocious development of their digestive DISCUSSION system. Tanaka et al.7 reported differentiated pyloric ceca at the first feeding and distinct Gastric evacuation rate expanded blind-sac at 10 DAH in Japanese Spanish mackerel. In the present study, the Elliott and Persson model13 was used to determine the daily food consumption of wild and reared Japanese Spanish Daily ration mackerel. This model requires the following two assumptions: (i) the rate of food consumption is Generally, the daily rations of larvae are greater in constant within the time interval between sam- warm water species than in cold water species. plings; and (ii) the rate of gastric evacuation (R) is Houde and Schekter24 studied the daily rations of exponential. Elliott and Persson13 showed that three subtropical larvae, ranging from 202 to 379% even if feeding is not constant, the first assumption body calorie for bay anchovy Anchoa mitchilli, is satisfied by collecting samples at intervals of 165–297% for lined sole Achirus lineatus, and within 3 h. In this study, this assumption was satis- 121–234% for sea bream Archosargus rhomboidalis. fied because of the shorter sampling intervals both Values of 42–160% for a dry bodyweight and 26–70% in the sea and in captivity. body calorie are found for summer flounder Prey type, water temperature, and predator size Paralichthys dentatus25 and northern anchovy are known to affect R in fishes.14–19 Durbin et al.17 Engraulis mordax,26 respectively. Yamashita and reported that fish was evacuated from the guts of Bailey23 observed a daily ration ranging from 21 to Gadoid fishes with greater R than that of crustacea. 51% of dry bodyweight for walleye pollock larvae. On the other hand, Buckel and Conover20 reported The values of temperate Japanese Spanish mackerel no significant difference in Rs for piscivorous age- larvae obtained here (90.6–111.7% for reared and 0 bluefish Pomatomus saltatrix among three dif- 111.1–127.2% for wild fish) were intermediate of ferent prey types tested (age-0 striped bass Morone those for the subtropical and subarctic species. saxatilis, bay anchovy Anchoa mitchilli, and age-0 Previous studies found smaller rations in wild Atlantic menhaden Brevoortia tyrannus). The larvae than in laboratory estimates.27–29 Hunter and similar estimated Rs for Japanese Spanish mack- Kimbrell30 estimated the daily ration for chub erel larvae (Table1) may reflect negligible influ- mackerel Scomber japonicus larvae as 87% of dry ences of morphology and energy content of larval bodyweight in captivity where food was plentiful. fish prey in this study. Peterson and Ausubel31 calculated 25–75% of dry 244 FISHERIES SCIENCE J Shoji et al.

bodyweight for wild Atlantic mackerel Scomber Misses Y. Kikuchi, M. Kurono, Mr K. Kamioka and scombrus larvae. These results and observations the staff of the Toyo Branch, Ehime Prefecture indicate that higher prey density would result in Chuyo Fisheries Experimental Station; and the higher consumption rates under rearing condi- members of fishing boats of Asagi-suisan Corp., tions. However, almost the same estimates of daily Fujita-suisan Corp., Saijo, Ehime, and Mekatsu- ration were obtained here for wild and reared suisan Corp., Kan-onji, Kagawa, for their kind help Japanese Spanish mackerel larvae. It may reflect in the field samplings; and the staff of Japan Sea- relatively high food availabilities for the wild larvae farming Association Yashima Station for their during the survey season resulting from peak assistance with the rearing experiments. Thanks occurrence of ichthyoplankton in the central Seto are due to Dr O. 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