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Rapp. P.-v. Réun. Cons. int. Explor. Mer, 178: 345-348. 1981.

INFLUENCE OF SALINITY AND TEMPERATURE ON EARLY LIFE STAGES OF COREGONUS ALBULA, C. LAVARETUS, R. RUTILUS, and L. LOTA

T. JÄGER, W. NELLEN. W. SCHÖFER, F. SHODJAl Institut für Meereskunde, Universität Kiel, Federal Republic of Germany

INTRODUCTION 100- Coregonus alb u la 10°C The cisco, Coregonus albula', the whitefish, C. 90 lavaretus\ and the roach, R. rutilus, are species which, B0 as adults, migrate into brackish water with salinities of 10 to 18 ”/oo or higher (Nellen, 1965). The burbot (L. lota) is a stenohaline limnic gadoid which spawns during the winter. 30

RESULTS 10 oJ 23%. C. ALBULA t t t _ i LARVAE ALEVINS in METAMORPH FRY I FRY II 1 36 54 127 AGE Idays) Larvae and juvenile stages were exposed to salinities g 10 22 39 LENGTH Imm) of 5 to 23 °/oo directly and in some experiments also Figure 1.Changes of salinity tolerance of early life stages of cisco stepwise. An experiment was finished when, in the case with age (Jäger, 1979). of larvae, at least 7 days after metamorphosis no respectively were observed (duration of experiment = further fish had died, and, in case of juveniles, no 25 days; n initially = 17,21, and 20 fish). 23 °/°° S (n = specimen had died for at least 7 days. Rearing 18) proved to be lethal, but when the salinity was temperature was kept constant at 10° C, and the food increased stepwise within a period of 30 days from 0.0 supply of Artemia nauplii was always provided in to 32.5 °/°° S few juveniles survived this high salinity excess. For each experiment 20-1 2 0 fish were used. for more than a month, i.e. to the end of the Yolk sac larvae survived in 5 to 12 °/oo S, and also experiment. in 15°/oo S when they were adapted stepwise. A Growth studies indicated that salinities up to stepwise adaptation was called “zoom”. Survival 15 °/°° S did not have any influence on growth when decreased with increasing salinity (Fig. 1). The initial compared with controls. But because of too few data number of fish when starting the experiment was 50. and a high variance this could not be demonstrated as Alevins 10-12 days before they had completed statistically significant. metamorphosis were more sensitive when transferred directly into brackish water. No reaction was found at C. LAVARETUS 5 °/oo S, but mortality soon reached 90% when the Eggs were fertilized in brackish water with salinities salinity increased to 107°° S. After metamorphosis of 1.8, 3.5, 5.9, 8.6, and 10.2°/oo S. Water intake into the fry became less sensitive. At an age of 54 days the perivitelline space and size increase of the egg due 15 °/oo S was tolerated (40% survival over 50 days, n to swelling was not apparently different from the fresh at start = 27 Fish), but 18 °/°° S proved to be fatal. The water reference. Larvae hatched from eggs incubated tolerance of 4.5 month old fry was even greater. At 15, in salinities of up to 10.2°/ooS . 18, and 20°/°° S survival rates of 95, 85, and 70% The larvae and juveniles of this species proved to 346 T. Jäger, W. Nellen, W. Schöfer, and F. Shodjai

withstand higher salinities earlier, and with greater 180 0%oS Rutilus rutilus success, than the equivalent stages of C. albula. — 1 8%oS Nevertheless the 4.5 month old fry also reached a final 170 3.5%o S 5 .2%o S threshold somewhere between 20 and 23 °/oo S (Fig. -S 16 0 - 2). When the fry was subjected to a gradual increase in — 8 6°/.S 10 2% oS salinity rather than an abrupt change the tolerance 150

limit was raised to more than 25 °/°° S. Alevins at the .£ HO beginning of metamorphosis (i.e. when the rest of the oil globule is resorbed) suffered a depression in salinity 130

tolerance, but not as pronounced as was the case with * 120 C. albula, and even during this sensitive development phase they were fully adapted to 15 7»» S when the

salinity was raised stepwise. Growth of yolk sac larvae 100 transferred to different salinities up to 15 7°° did not

show statistically significant differences for a period of 10 100 hours more than 100 days. Figure 3. Relative increase in the diameter of freshly spawned roach eggs at different salinities (Schöfer, 1979). R. RUTILUS Eggs were either fertilized in fresh water and transferred to salinities of 1.8, 3.5, 5.2, 6.9, 8.6, and When fertilization took place in freshwater and the 10.2 7 ° ° S after 10 or 20 min, or directly fertilized in eggs were transferred into brackish water after 10-20 these salinities. min, a positive preconditioning of the egg was When fertilized in fresh water (temperature 14.6° C) observed which caused surprising events during the eggs started to swell due to water uptake. This embryonic development. process took 45 min after which the egg measured In the freshwater control hatching of the larvae about 130% of its initial size (Fig. 3). started on day 11, by which time the embryo had Starting from fertilization salinities of 3.5 °/00 S reached stage IX of development, and ended on day and higher slowed down the swelling process, but the 13. time of water uptake was prolonged, so that after 48 h In 8.6 and 10.2 7 oo S the eggs swelled up the egg diameter might have increased to 160% of its considerably during the first day and most were burst original size. on the second day. No embryonic development was All eggs which had been directly fertilized in observed. brackish water of 3.5 °/oo S and more died before any In salinities of 1.8 to 6.9 °joo the embryos hatched at embryo had hatched. In 1.8 7°° S development of the earlier developmental stages. The earliest embryos embryo and hatching was almost normal. In 3.5 °/ oo S hatched were of stage III. From the beginning of the the last eggs died during day 10, shortly before eyed stage free-living embryos were common in all hatching. Although fertilization success in salinities of salinities. The embryos hatched from a chorion in a deteriorated condition and continued development at 8.6 and 10.2 °/oo S was as high as in the control (>95%) all of the eggs died within 4 and 3 days, the bottom of the vial. Mortality of eggs and especially respectively. of free living embryos was considerable, and increased with salinity. The results suggest that the biochemical processes 90- which condition the perivitelline space and the chorion 80- of the roach egg are highly dependent on the condition 70- < at fertilization. Although the mortality rate of larvae fertilized and cultured in 3.5-6.9 7oo S decreased after they reached stage IX they all died during metamorphosis. In water of 1.8 7oo S the mortality rate still increased but 20% of the original eggs survived well beyond larval metamorphosis. In fresh water 60% of the eggs could be reared to juvenile fish.

LARVAE ALEVINS in FRY I FRY II METAMORPH While embryonic development in brackish water 1 2L 42 131 AGE (days) 12 18 21 39 LENGTH Imm) did not bring about any adaptation, development at a Figure 2. Changes of salinity tolerance of early life stages of salinity of 3.5 °/oo and even 6.9 °/ oo S did not cause whitefish with age. irreversible damage to the larvae. Once they were Salinity, Temperature, and Early Life Stages of Coregonus 347

Rutilus rutilus 15°-19°C transferred to freshwater further growth proceeded 100- normally. Resistance to brackish water increased only with age (Fig. 4).

/ . . LOTA < The burbot is the only limnic representative of the > 5?Û- big gadid family. Although it probably originates from 50 z marine ancestors L. lota does not enter mesohaline (T brackish waters at all. The results from burbot eggs exposed to different salinities were surprising. Embryonic development from fertilization and hatching of larvae was observed 0 in salinities of up to 12 °/oo. At 3 and6°/oo S overall JUVENILES mortality was only 9% which did not deviate from 1 8 20 83 1 year results obtained in freshwater. At 9 and 12°/°° S, Figure 4. Changes of salinity tolerance of early life stages of roach respectively, only 74% and 27% of the eggs finally with age. survived to free living larvae. The mortality rate increased at later embryonic stages and at 12°/oo

deformed larvae occurred. At a salinity of 14°/oo this 1 0 0 - malfunction increased to such a degree that no viable Lota lota larvae could hatch. Burbot eggs proved to be very stenothermal. The temperature range in which embryonic development occurred was narrow and did not extend far beyond 7° C. The lowest temperature which could be tolerated was close to 1°C (Fig. 5). Survival of eggs decreased

rapidly when the temperature deviated from 4° C. This 50- physiological reaction seems to be in good agreement with the reproduction ecology of L. lota, as the burbot spawns during the coldest time of the year often under­ y= -3432 *63 6x -838x2 neath an ice cover. t max = 3.8°C The highest sensitivity of suboptimal temperatures was observed in the early embryonic stages. The length of the larvae at hatching was also influenced by suboptimal temperatures, and it seems anomalous

that the biggest larvae hatched at 4° C rather than at 2 4 6 7 °C 2°C: TEMPERATURE Figure 5. Percent survival to hatching of burbot eggs at different temperatures (Shodjai, 1977). Length of Time of larvae, x incubation ° c n mm s days DISCUSSION

2 35 3.74 ±0.08 52 Physiological reactions of early life stages of the 4 40 3.90 ±0.08 31 four fresh water fish species cisco, whitefish, roach, 6 30 3.60 ±0.04 21 and burbot were mainly studied from the ecological 7 18 3.30 ±0.09 18 aspect. As transitional zones between fresh and saline water are common around the Baltic coasts, the The differences were significant at the 0.1% level. question of adaptation of fresh water fish to brackish water conditions is of regional and general interest. Temperatures around 4°C proved to be essential Our results on the salinity tolerance of the early life only during the early ontogeny of the burbot. The stages of cisco, whitefish, and roach are well in larvae did not start feeding and died if kept at accordance with their reproductive ecology; C. albula temperatures less than 8°C for a longer period. inhabits lakes. C. lavaretus forms anadromous Survival of larvae beyond metamorphosis was equally populations located in rivers flowing into the North good at water temperatures of 8° to 20° C. Sea and the Western Baltic. The two Coregonus spp. 348 T. Jäger, W. Nellen, W. Schöfer, and F. Shodjai produce non-adhesive semi-buoyant eggs, and C. stability can most likely be expected at winter lavaretus at least may spawn in the lower reaches of a underneath the ice, where deviations from 4°C are river (Thienemann, 1937; Lindroth, 1957). So it is seldom. likely that young larvae or even eggs get transported Eggs of typical freshwater fish, especially those into the estuary and are subjected to brackish water. spawning during spring or early summer, as roach or If we assume that the Teleostei originated primarily perch, for instance, tolerate a considerable range of from limnic environments C. lavaretus seems to have temperatures during their development (Kokurewicz, the potential to develop into a marine species. This 1970; Lieder, 1955; Einsele, 1961; Bette, 1970). species can be regarded as being in a rapid Apart from their ecological interest, the evolutionary situation which is indicated by the many experimental results obtained in our work have some sub-species found in the areas of its distribution value for applied fishery biology. Artificial (Nellen, 1979). propagation of coregonids and stocking of coastal Obviously C. albula is not as successful in waters having a high nutrient value for fish seem to be establishing anadromous populations as C. lavaretus. possible. C. lavaretus also looks promising for This may be due to the higher sensitivity of its mariculture. prolarvae to salinity. The roach also migrates into mesohaline water. It spawns adhesive eggs. During our own field research we never detected any eggs or fry of cyprinids in reed REFERENCES areas which grew in the shallows of brackish water Bette, T., 1970. Umweltfaktoren und Mi ß bildungen bei der Brut fjords. This fish family is represented mainly by limnic von Blaufelchen (Coregonus wartmanni Bloch). Diss. Univ. stenohaline species, some of which occasionally München, Naturwiss. Fak. Hohenheim. 66 pp. penetrate into brackish water fjords as adults. But this Einsele, W. 1961. Fischereiwissenschaft. Verh. Int. Ver. Limnol. 14: group developed genetically in inland waters and 806-819. became ecologically well established here during the Jäger, T. 1979. Untersuchungen zur Salzgehaltstolesanz und zur course of evolution. This may be best documented by Aufrucht des Larven und Jungfische von Coregonus lavaretus L. the high sensitivity of its eggs and larvae to even very und C. albula L. Diploma Thesis, Univ. Kiel, 104 00. low salinity levels. Kokurewicz, B. 1970. The effect of temperature on embryonic The burbot seems to be a well established freshwater development of Tinea tinea L. and Rutilus rutilus L. Zoologica species which avoids brackish waters completely. But Poloniae 20: 317-337. Lieder, U. 1955. Uber die Temperaturempfindlichkeit von it is likely that this biological characteristic has to be Fischeiern. Dt. Fischereizeitung 2: 12-15. regarded as a secondary process of evolution. L. lota Lindroth, A. 1957. A study of the whitefish (Coregonus) of the probably colonized the limnic environment from the Sundsvall Bay district. Rept. Inst. Freshw. Res. Drottningholm sea because all other species of the gadid family are 38: 70-108. stenohaline marine fish. The high tolerance limit of the Nellen, W. 1965. Beiträge zur Brackwiasserökologie der Fische im burbot eggs to brackish water may be an indication of Ostseeraum. Kiel. Meeresforsch. 21: 192-198. the marine origin of this species, although this capacity Nellen, W. 1979. Neuere Ergebnisse zur Systematik und Biologie is now irrelevant from the ecological point of view. der Coregonen und ihre Bedeutung für die Aquakultur. Der Another indication of the marine origin of the Fischwirt 29: 67-72. burbot may be seen in the extreme stenothermal Schöfer, W. 1979. Untersuchungen zur Fortpllauzungs fähigkiet der Plötze (Rutilus rutilus L.) in Brackwasser. Arch. Hydrobiol. reaction of its eggs. Freshwaters are usually 86: 371-395. characterized by a more unstable environment Shodjai, F. 1977. Ein Beitrag zur Embryonal-und Larvelentwick- compared to the ocean. Because the burbot is a gadid, lung der Quappe (Lota Iota L.) in Abhängigkeit von der it should be expected to spawn in winter time. If the Temperatur. Diploma Thesis, Univ. Kiel, 97 pp. physiology of its early life stages is still influenced by Thienemann, A. 1937. Die Schlei und ihre Fischereiwirtschaft. Der the marine ancestry that demands relative stability in Schleischnäpel (Coregonus lavaretus balticus). Schriften des the environment, then, with regard to temperature, Naturwiss. Vereins Schleswig-Holstein 22: 190-208.