by Samuel F. Hildebrand (1939)
Introduction . . . . . . . . . . . . . . . Page 15
Whether the Panama Canal serves as a passageway for fishes, permitting at least some of the species of the opposite oceans to cross the Isthmus, has been a subject of conjecture ever since the Canal was built. It was questioned whether fish could successfully negotiate the locks, and if so whether any of them could endure the journey of about 40 miles through the fresh water between the locks at the opposite ends of the Canal. It is now possible to give limited information on these questions, and on the animal life in the locks in general, as a result of observations and collections made in 1935 and 1937, together with subsequent study.
This work was made possible largely through the financial aid given by Dr. Herbert C. Clark, Director of the Gorgas Memorial Laboratory, to whom the writer is greatly indebted also for numerous other courtesies. He is deeply appreciative also of the extensive help given by Dr. A. O. Foster of the Gorgas Memorial Laboratory, and in fact to the entire staff of that laboratory.
Officers of the Panama Canal, as well as more than a few employees, too, [[p. 16]] gave valuable aid. Among them are Col. C. S. Ridley, Governor; Col. Glen E. Edgerton, Engineer of Maintenance; Maj. W. D. Styer, Assistant Engineer of Maintenance; R. Z. Kirkpatrick, Chief of Surveys; E. D. Stillwell,. Superintendent of Locks; H. M. Thomas and J. C. Myrick, Assistant Superintendents of Locks; Fred Whaler, Carl G. Brown, S. A. Venable, R. A. Cauthors and many others who cannot be named for want of space. Special mention must be made of the extensive aid and many courtesies extended by W. H. W. Komp, medical entomologist, U. S. Public Health Service; and J. B. Shropshire, malariologist, U. S. Army.
The writer is deeply grateful, also, to the several taxonomists, who identified various groups of animals collected. These specialists are named in the text in connection with the discussion of specimens identified by them. To these workers, who gave of their time and energy, the writer especially wishes to extend thanks.
One or more specimens of the species herein named, whether fish or invertebrates, have been or will be deposited in the U. S. National Museum.
Observations and collections were made in Gatun Locks, on the Atlantic side, during the early months of 1935, and in Pedro Miguel and Miraflores Locks, on the Pacific side, during the early part of 1937, when the writer was present to witness the dewatering of one side of each lock. The water is removed, partly by draining and partly by pumping, from the locks at intervals of about three years for the purpose of cleaning and generally overhauling them. Collections were made by others in the sides dewatered during the writer's absence. A particularly fine collection was secured in the east side of Miraflores Locks under the supervision of Dr. A. O. Foster of the Gorgas Memorial Laboratory. Representative specimens, as far as possible, were preserved from among the fishes and invertebrates stranded in the locks as the water was removed. Collections were made also in the fresh waters situated between the locks at the opposite ends of the Canal, as well as at several places on both shores of the Isthmus and some of the outlying islands.2
REMARKS CONCERNING THE CANAL AND LOCKS.
For the convenience of the reader who has not seen the Panama Canal, it may be stated that the general direction of the Canal is somewhat west of north and east of south, though traffic is designated as "north and south bound."
The Atlantic terminus of the Canal is entered from Limon Bay. A vessel sailing from the Atlantic to the Pacific, that is, southbound, proceeds at sea level as far as Gatun, a distance of 6 or 7 miles from Cristobal, the Atlantic port. There the Gatun Locks are reached. These locks, like those at the other end of the Canal, are double, permitting two-way traffic, the two channels of the locks commonly being designated the east and west side. The Gatun Locks consist of three equal flights whereby a southbound ship is lifted approximately 85 feet, to the level of Gatun Lake, which lies beyond the locks.
Gatun Lake is a large body of fresh water, having an area of about 196 square miles, created by damming the Chagres River. Though the deep water, that is, the course for vessels, is well marked with buoys and beacons in Gatun Lake, a definite channel or canal is not visible for a distance of somewhat more than 20 miles. Thereupon Culebra (or Gillard) Cut, is [[p. 17]] reached. This cut, through the continental divide, is about 9 miles long, and leads to Pedro Miguel Locks.
The Pedro Miguel Locks consist of a single flight, whereby a southbound vessel is lowered from the approximately 85-foot level of Gatun Lake to a level of about 53 feet of Miraflores Lake, which lies below these locks.
Miraflores Lake is a small body of fresh or brackish water (sometimes slightly brackish from lockage water when northbound traffic is heavy), scarcely 2 miles long in the direction of the Canal. A southbound vessel reaches the Miraflores Locks after crossing this small lake.
The Miraflores Locks consist of two equal flights whereby a southbound ship is lowered to sea level. The vessel now follows a rather definite channel (canal) to Balboa, the Pacific port of the Canal, a distance of about 4 miles, and then enters Panama Bay.
In passing a northbound ship through the Canal the processes described in the foregoing paragraphs are, of course, merely reversed. As already indicated the locks are double, making it possible to pass two vessels through them simultaneously either in the same or opposite directions.
THE LOCKS AS PHYSICAL BARRIERS.
The locks do not constitute serious physical barriers to fish, as explained at some length by the writer in a paper entitled, "The Tarpon in the Panama Canal" (Scientific Monthly, Vol. 44, Mar., 1937, pp. 245-246). Obviously fish may swim into the upper or lower chambers of the locks without meeting any obstruction whatever when the gates at the opposite ends of the locks are open. There they may remain more or less indefinitely, or they may follow the next ship through the locks. In the case of the Gatun Locks, with three flights, they could ascend from the lowest to the middle chamber with a southbound vessel, or descend to this chamber from the uppermost level with a northbound vessel. There they might remain for a time, or complete the transit through the locks with a single ship. It is understood, of course, that when the lock gates are open, as in passing a ship from one chamber to the next one, no physical obstruction remains to prevent the fish from following the vessel.
DIFFERENCE IN SALINITY A BARRIER.
The change in salinity from fresh to salt water or vice versa, depending upon the direction a fish may be pursuing, in going through Gatun or Miraflores Locks (this does not apply to Pedro Miguel Locks, as they are in fresh water), is a much more formidable barrier, to most fishes, than the locks themselves.
That many marine fish enter the locks and go through a part of the way, at least, is evident from the large number present at each dewatering. Several marine and brackish water species appear to live in the locks indefinite periods of time, and a few probably are permanent residents. It is to be noted, however, that strictly fresh water species seem to avoid the locks, as very few individuals or species were present even in the fresh water of the Pedro Miguel Locks, and in the nearly fresh water of the upper chamber of Gatun Locks. The abundance of fish in the middle and lowest chambers of Gatun Locks and both Chambers of Miraflores Locks suggests that food probably is plentiful and that conditions otherwise are agreeable to a comparatively large number of salt and brackish water species, as shown by the lists appended.
The temperatures and particularly the salinities, as already pointed out, profoundly affect the animal life in different parts of the Canal. The tables [[p. 18]] and some of the other data offered were very kindly furnished by R. Z. Kirkpatrick, Chief of Surveys of the Panama Canal. The temperatures, given in Table I, are a summary of records covering the period from 1908 to 1936 inclusive for Balboa and Colon, and from November, 1918, to December, 1936, inclusive for Gatun Lake. The period of time covered by the records of salinity given in Table II, was not furnished.
The "Pacific Entrance (Inner Harbor)" and the "Atlantic Entrance (Inner Harbor)" temperatures, as well as the salinities, were taken respectively at the Balboa and Cristobal Docks.
On the Pacific side a cold water period occurs during the dry season. Concerning this Mr. Kirkpatrick said: "Cold water period is from February to April; it is caused by Antarctic colder water being welled-up over Panama Bay Bottom Shelf during these months." As understood by the writer, the brisk trade winds blowing across the Isthmus from the Atlantic to the Pacific have something to do with the up-welling of cold water in Panama Bay, as they tend to drive the warm surface water off shore.
Outside the inner harbor the water temperatures apparently drop considerably lower, as shown by some records kindly furnished by W. H. W. Komp, U. S. Public Health Service. Mr. Komp took the water temperatures with a pocket thermometer at Amador Beach during the dry seasons of 1934, 1935, 1936 and 1937. Each season, exclusive of 1937, the temperatures ranged downward into the sixties, the lowest occurring in 1934 when the water along the beach, between 4 and 5 o'clock in the afternoon, ranged in temperature from 60.5° to 63° F. from Feb. 11 to 16.
These low temperatures affect fishing profoundly in Panama Bay, as such important game fishes as the sailfish, marlin, and dolphin are missing during this season. On the other hand, the corbina (sea trout or weakfish) seem to become more numerous. The cold water probably causes the fish population to vary to some extent with the season also in Miraflores Locks.
Tides and lockage water have a direct bearing on salinity at both ends of the Canal. Mr. Kirkpatrick stated: "Tidal ranges on the Pacific side vary between an elevation of +11.0 and -10.5 feet, with a mean range of about 12.6 feet. . . . Tidal ranges on the Atlantic side do not exceed 24 inches." He stated furthermore, "Inner harbor salinities and densities are affected, of course, by the down-lockage of fresh water from Miraflores and Gatun Lakes." It is understood, of course, that the chambers of the locks in passing ships through them are filled with water admitted from the lakes above them, which in each instance is fresh (except for the slight brackishness occurring at times in Miraflores Lake). Therefore, if traffic is heavy a large amount of fresh water reaches the sea level ends of the Canal, reducing the percentage of salinity. It is evident, then, that the water in the locks (exclusive of that in Pedro Miguel Locks, which are in fresh water) may vary from about the saline condition of the inner harbor, when the sea level gates are open, to a sort of half and half mixture of the harbor and lake water to almost fresh, as in the upper flight of Gatun Locks.
Salinity records for the locks are not available, except for one day (June 10, 1935), and for Gatun Locks only. According to hydrometer readings furnished by Mr. Kirkpatrick (without making corrections for temperature) the chambers of the upper level were fresh. No appreciable amount of salt was indicated in the east chamber of the intermediate level immediately after the water had been lowered from a 71- to a 43-foot level, and only slight brackishness was evident in the west chamber of the same level after it had been filled from a 43- to a 71-foot level. The two lowest chambers, however, were decidedly brackish, the salinity varying from about 10,000 to 16,000 parts per million. At the Atlantic entrance (outside the locks) the water was about as salty as that shown for the "Atlantic Entrance (inner harbor)" in Table II.
It is claimed by employees of the Canal that when the Gatun Locks first were operated dead fish were seen in the locks from time to time, which presumably died from the change in salinity caused by filling the locks with fresh water from Gatun Lake. Dead fish no longer are seen. The employees believe the fish have become "educated" to the necessity of avoiding fresh water.
The extent to which marine fishes have invaded fresh water, nevertheless, is remarkable, as shown by the large number of salt water species listed from fresh or nearly fresh water subsequently. This is true especially of Miraflores Lake where fresh and salt water species seemingly intermingle freely.
FISHES USING THE CANAL AND LOCKS AS PASSAGEWAYS.
The species that most logically would be expected to pass through the locks and possibly complete the transit from ocean to ocean, are those inhabiting more or less indiscriminately salt, brackish and fresh water. To this group of fishes in Panama belong some of the guavinas (Gobiidae), several species of snook or robalos (Centropomidae), some of the so-called marine mojarras (Gerridae), a few species of rancons or burros (Pomadasys), and the tarpon (Tarpon atlanticus).
Among the fishes named the tarpon definitely has completed the transit from the Atlantic to the Pacific, as 4 individuals were present in the lower chamber of Miraflores Locks (east side) when dewatered in 1937. When the gates to the lower flight of the locks are open, as they often are, when [[p. 20]] vessels are not actually in transit, nothing remains to prevent the fish from swimming into the sea level end of the Canal and out into Panama Bay.
Tarpons, indeed, have been reliably reported from the Pacific sea level terminus of the Canal, though to date this fish does not seem to have been caught in Panama Bay. While tarpons are present in Gatun Lake at all times, there is as yet no evidence that this fish breeds there, as pointed out by the writer (Scientific Monthly, Vol. 44, Mar., 1937, p. 242). Therefore, it may be assumed, for the present at least, that the fish came from the Atlantic (or Caribbean Sea); that they use Gatun Locks as a passageway to Gatun Lake whence they pass on through Culebra Cut, and the Pedro Miguel Locks into Miraflores Lake (where they are seen frequently), and then on through the Miraflores Locks.
Among the guavinas, or fresh water gobies, which inhabit principally fresh and brackish water, Dormitator maculatus of the Atlantic slope and shores was taken in the lower chamber, that is, at sea level, of Miraflores Locks. Leptophilypinus fluviatilis, another species of the Atlantic side, also was taken in Miraflores Locks, though not in the lower chambers. This species was numerous in the Pedro Miguel Locks and one specimen was secured in Miraflores Lake. On the other hand, Gobiomorus maculatus, a species of the Pacific side, was secured in Gatun Lake in company with its near relative Gobiomorus dormitor, of the Atlantic side. Gobiomorus maculatus is very common in Miraflores Lake, though it was not taken in Pedro Miguel Locks. It conceivably could have reached Gatun Lake without passing through the locks, as a few small Pacific slope streams empty into the Canal above Pedro Miguel Locks. Finally, it seems probable that Eleotris pisonis, of the Atlantic side, has crossed over to the Pacific, as shown by some specimens taken in the lower chamber of Miraflores Locks, which appear to be hybrids, that is, a cross between Eleotris pisonis and E. picta. No typical examples of E. pisonis were taken, however, on the Pacific side.
Among the snooks or robalos, some of which range from the shores far up freshwater streams, Centropomus parallelus, an Atlantic side species, was taken in Miraflores Lake. To reach this lake the fish had to pass through Pedro Miguel Locks. Centropomus pectinatus, which occurs on both coasts of Panama, also was taken in Miraflores Lake. Because of its natural distribution this species may have come from either coast. No positive proof has been found, so far as the writer is aware, that any of the snooks breed in fresh water.
Two species of mojarra (Gerridae), namely, Eucinostomus californiensis3 and Gerres cinereus, were taken in the locks and the latter also in Miraflores Lake. However, as these species are common to both coasts of Panama it is not known that they have traversed the Isthmus, though they probably pass through the locks freely.
Specimens of rancon or burro (Pomadasys) were taken in Gatun Lake, and in Pedro Miguel Locks and Miraflores Lake. These specimens all appear to be one species, but it is not possible at this time to state whether they are Pomadasys crocro from the Atlantic or P. bayanus from the Pacific, two nominal species which may not be distinct. Though these fish seem to pass through the locks, it has not been determined whether they have crossed the Isthmus. Neither is it known that they breed in fresh water, though they frequent it.
The small anchovy, Anchovia parva, present in large numbers in all three chambers of Gatun Locks in 1935, was common in both chambers of Miraflores Locks in 1937. As this species has not been recorded from the Pacific, it seems possible that a migration has taken place, though it was not taken in Gatun Lake, Pedro Miguel Locks nor Miraflores Lake.
The silverside, Menidia (Thyrina) chagresi, though belonging to a [[p. 21]] family whose members are mostly marine, lives in fresh and brackish water. It was found common in the Chagres Basin during our investigations in 1911 and 1912, before the opening of the Canal. In 1935 it was found in the middle and uppermost chambers in Gatun Locks, and numerous in Gatun Lake. In 1937 several specimens were secured in Pedro Miguel Locks and the lower chamber of Miraflores Locks, presumably a result of a migration from the Atlantic to the Pacific slope through Culebra Cut.
Among the more or less strictly fresh water species the chogorro, Cichlasoma maculicauda, an Atlantic slope fish sometimes descending to slightly brackish water, seems to have crossed to the Pacific side, as it was taken in Pedro Miguel Locks, Miraflores Lake and the upper chamber of Miraflores Locks, as well as in the Gatun Locks. Two Atlantic slope species of "sabalo pipon," Brycon chagrensis and B. petrosus, were taken on the Pacific side, the former in Pedro Miguel Locks and Miraflores Lake, and the latter in the Rio Cocoli, a short distance above Miraflores Lake.
Only one of the numerous species and generally abundant "sardinas," namely Astyanax fasciatus, a Pacific slope species, seems definitely to have crossed the divide through Culebra Cut, as it was taken in Gatun Lake. Other species of characins may have crossed through Culebra Cut. However, as several species of this family are common to both slopes, crossing over cannot be determined from specimens.
It was particularly surprising that the abundant "sardina," Astyanax ruberrimus, of both slopes, which literally swarms everywhere in Gatun and Miraflores Lakes, did not occur in the locks. Not one specimen even was found in Pedro Miguel Locks, which are in fresh water, though it occurs in abundance above and below them. It was rather surprising also that Roeboides, another "sardina," avoids the locks, wherein no specimen was secured. Furthermore, no crossing over nor intermingling of the two easily distinguishable species, guatemalensis of the Atlantic slope and occidentalis of the Pacific, through Culebra Cut, seems to have taken place, as shown by numerous specimens collected in Gatun and Miraflores Lakes.
The pipefish, Doryrhamphus (Oostethus) lineatus, has been reported as having been caught "in transit through the Panama Canal" by Chickering (Copeia, No. 173, 1930, p. 85). However, this fish probably inhabits chiefly fresh and brackish water as shown by many specimens taken during our investigation in 1911 and 1912 (Meek and Hildebrand, Field Mus. Nat. Hist. Pub., Zool. Ser., XV, Pt. I, 1923, p. 262), before the opening of the Canal, when none was secured in salt water. In March, 1935, the writer collected 9 specimens in a few hours seining along the shores of Barro Colorado Island, in Gatun Lake. Four of the specimens are males with abdominal pouches filled with eggs, showing that this fish breeds in the Lake, where it probably is a permanent residence. It was not seen in any of the locks, nor in Miraflores Lake. Therefore, it is not known that it frequents the locks, nor that it has crossed the divide through Culebra Cut.
INVERTEBRATES OBSERVED AND COLLECTED.
It is stated in the foregoing pages that some fishes are so numerous in parts of the locks at each dewatering (see appended lists for the relative abundance of the various species of fishes observed in the chambers of the locks) that they must find conditions agreeable. In this connection a brief account of the condition of each lock, together with remarks on the invertebrates observed, seems desirable. Many of these lower forms of course are eaten by fish.
The collections of invertebrates of necessity are incomplete, as the water drops rapidly in the dewatering process. After the floors of the different chambers become exposed water remains only in the "manholes" in the floors, and in the sumps, at the gates. Some animals are stranded, but [[p. 22]] many more of the free swimming forms manage to reach either the bottom holes or the sumps. In any event, collections must be made quickly. As the writer and his helpers were interested chiefly in securing a representative collection of fishes, to which they gave most of their attention, more than a few invertebrates, even of the larger forms, no doubt escaped notice. Therefore, the collections of these lower forms must be considered far from complete.
Gatun Locks: The walls and floors of Gatun Locks (east side), when de-watered in 1935, had not accumulated much sediment or rubbish since the previous overhaul in 1932, though sufficient slush was present on the bottom that the collectors were well covered with mud splattered by stranded fish. Neither were the growths on the walls, gates and floors especially luxuriant. The growth in the uppermost and middle chambers consisted mostly of a hydroid, identified by Prof. Charles McLean Fraser as Cordylophora lacustris Allman. This hydroid was most abundant in the nearly fresh water of the uppermost chamber, and little in evidence in the much saltier lowest chamber, wherein that growth was largely replaced by oysters and barnacles.
Clusters of mussel-like bivalves, examples of which were identified as Brachidontes exustus Linnaeus by Dr. Paul Bartsch, who furnished identification also for the other molluscs mentioned herein, were present in the middle and lowest chambers of Gatun Locks. The gastropod, Neritina meleagris Lam., was numerous in the uppermost chamber, less so in the middle one, and was not observed in the lowest chamber.
Small crabs were present in each chamber of Gatun Locks. However, examples were preserved only from the uppermost one. These were identified by Dr. Mary J. Rathbun, who identified the other crabs mentioned herein also, as Callinectes sapidus acutidens Rathbun, and who supplied the following note, "A marine species ranging from each coast of Florida to Rio de Janeiro, Brazil." This crab was inhabiting the nearly fresh water in the uppermost chamber of Gatun Locks.
Small shrimps, too, were present in the Gatun Locks. One species, identified as Macrobrachium acanthurus (Wiegmann) by Dr. Waldo L. Schmitt, who identified the other shrimps mentioned herein also, was taken only in the lowest chamber, though it may have been present in the others. Dr. Schmitt remarked, "A fresh water species, ranging from Florida to Brazil and Uruguay, and West Coast of Mexico to Ecuador." Juveniles of another species, provisionally identified as Macrobrachium olfersii (Wiegmann), were common in the uppermost chamber, and a third species, Crangon armillatus (H. Milne-Edwards), was taken in the lowest chamber. Concerning the latter Dr. Schmitt remarked, "A marine species distributed from North Carolina and Bermuda to Brazil; and through the West Indies."
One specimen of Macrobrachium olfersii was infested with a bopyrid isopod in the right branchial cavity. This isopod was identified by J. O. Maloney as Palaegyge meeki Richardson.
Pedro Miguel Locks: The Pedro Miguel Locks, which are in fresh water, though possibly at times very slightly brackish from lockage water from Miraflores Locks, contained mud several inches to a few feet deep (east side). The concrete walls and the iron gates, as high as the permanent water level, were almost entirely covered with a mussel-like bivalve, identified by Dr. Bartsch as Congeria (Mytilopsis) sallei Recluz. On the floors of the locks, where objects for attachment were present, clumps of this bivalve also occurred, and under and around the clumps amphipods, probably of the same species as the one from the upper chamber of Miraflores Locks, identified as Grandidierella megnae (Giles) by C. R. Shoemaker, were numerous. Unfortunately the specimens collected were lost. No other molluscs or amphipods were noticed, though they may have been present.
Shrimps were rather common, and no doubt are fed upon by some of the fish that inhabit these locks. Dr. Schmitt identified 4 species, namely, [[p. 23]] Penaeus stylirostris Stimpson, Macrobrachium jamaicense (Herbst), M. acanthurus (Wiegmann), and Palaemonetes sp. Dr. Schmitt referred to the one first named as a marine species, the next two as well known fresh water shrimps, and the last one as most likely a fresh water form. No crabs were seen in these locks.
Miraflores Locks: The fauna of the Miraflores Locks was much more diversified than that of the Pedro Miguel Locks, no doubt because the water ranges from salt to nearly fresh. The upper chamber contained fully as much sediment as the Pedro Miguel Locks, but the lower one contained much less. The walls of the upper chamber were almost as fully over-grown as Pedro Miguel Locks with the same species of bivalve, but in the lower chamber this mollusc was missing, presumably because of the higher salinity. This bivalve occurred also in clusters on the floor of the upper chamber wherever there were objects reaching above the bottom slush to which it could attach itself. Among these clusters were numerous amphipods, presumably all of the species identified as Grandidierella megnae (Giles) by Mr. Shoemaker from the single specimen, of many collected, not lost in shipment.
In addition to the abundant bivalve mollusc a scant growth of a hydroid, somewhat doubtfully identified (because of the unsatisfactory condition of the specimens) as Bimeria gracilia Clark by Prof. Fraser, was present in the upper chamber. In the lower chamber only a few clumps of the hydroid were seen attached to objects on the floor.
The abundant growths of the bivalve and hydroid mentioned, of the upper chamber, were replaced in large part by barnacles in the lower one. A few other attached forms of which only scattered examples were seen, was the sponge, identified by M. W. de Laubenfels as a cosmopolitan form, Haliclona permollis (Bowerbank), and the alcyonarian, Leptogorgia alba Duchassaing & Michelotti, as identified by Miss Elisabeth Deichmann, who referred to it as "one of the most common forms in the lava pools off Panama."
In the lower chamber of Miraflores Locks the wooden beams against which the bottoms of the iron gates close were badly infested with teredo, of which no examples were secured. Only one mollusc, the gastropod, Thais kiosquiformis Duclos, in addition to the numerous bivalve already mentioned, was taken in the upper chamber. This gastropod was found also in the lower chamber with four others, identified by Dr. Bartsch as Phyllonotus radix Gmelin, Pustularia pustutala Lamark, Triumphis distorta Wood, and Cymatium (Linatella) wiegmanni Anton. Limpids were fairly common in the lower chamber. Examples of two species, Crepidula aculeata Gmelin and C. incurva Broderip, were preserved. Small squids were common in the sump at the lowest gates of the locks. The examples transmitted to the National Museum were identified as Loligo sp.
Crabs and shrimps were in evidence in both chambers of Miraflores Locks and were numerous in the bottom holes after the water had been pumped somewhat below floor level. The crabs in particular were difficult to catch in these holes, as they clung closely to the walls from which they were not readily removed, and generally dived out of reach of a dipnet after some agitation. Because of the difficulty of catching crabs and shrimps, and more particularly because of lack of time, more than a few species surely were missed.
Only two species of crab, identified by Dr. Rathbun as Panopeus rugosus A.M.E., and Callinectes arcuatus Ordway, were collected in the upper chambers. These two were taken also in the lower chamber with Panopeus chilensis M. Edw. & Lucas and Petrolisthes armatus (Gibbes). The occurrence of the blue crab, Callinectes sapidus Rathbun in fresh water recently was discussed by Gordon Gunter (Science, Vol. 87, Jan. 28, 1938, p. 87). It is not surprising, therefore, that other species of the genus also enter brackish and fresh water.
[[p. 24]] Seven species of shrimp were collected in the upper chambers of Miraflores Locks, which Dr. Schmitt identified as Penaeus brevirostris Kingsley, Macrobrachium jamaicense (Herbst), M. acanthurus (Wiegmann), Palaemonetes sp., and two species of snapping shrimp, Crangon, unidentifiable as to species because of the "meager and incomplete material" and because of "our too limited knowledge of the west American species."
Four species of shrimp collected in the upper chambers, namely Macrobrachium acanthurus (Wiegmann), Palaemonetes sp., and the two unidentifiable species of Crangon, were taken also in the lower chamber, with the three following species not secured in the upper one: Penaeus stylirostris Stimpson, P. occidentalis Streets and a third unidentifiable Crangon. Besides the shrimps, a stomatopod, Chloridella aculeata (Bigelow), was taken.
Dr. Schmitt referred to Macrobrachium jamaicense (taken in Pedro Miguel Locks and the upper chamber of Miraflores Locks), and M. acanthurus (found in all three levels) as "well known fresh water shrimps," and he regarded it likely that Palaemonetes sp. (taken in all three levels) also is a fresh water form. Though these species live chiefly in fresh water they appear to enter brackish water, or even at times salt water. The rest of the shrimps apparently may be regarded as salt and brackish water forms.
ANNOTATED LIST OF FISHES FROM THE LOCKS OF THE PANAMA CANAL.
The nomenclature and sequence of families of the earlier works by Meek & Hildebrand (a. "The Fishes of the Fresh Waters of Panama," Field Mus. Nat. Hist. Pub., Zool. Ser., X, No. 15, 1916, pp. 217-374; b. "The Marine Fishes of Panama," Field Mus. Nat. Hist. Pub., Zool. Ser., XV, No. 215, Pt. I, 1923; No. 226, Pt. II, 1925; and No. 249, Pt. III, 1928, 1045 pages) have been followed as far as it seemed permissible to do so. In order to retain as far as possible this nomenclature and sequence, the rearrangement and splitting of some of the old families (as for example Siluridae, Serranidae, Sciaenidae, and Gobiidae), as well as some of the genera, by some recent writers have not been adopted. This course was followed chiefly for the convenience of those perhaps not entirely familiar with the nomenclature who may wish to check the lists against the descriptions and accounts in the earlier publications.
The large number of marine species present in the locks and their great tolerance for fresh or nearly fresh water are interesting facts shown in these lists. . . .
1. Published by
permission of U. S. Commissioner of Fisheries. [[on