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BULLETIN OF THE UNITED STATES FISH COMMISSION 1886
NOTES ON LOBSTER CULTURE. PART 1 ......... PART 2......... PART 3
EXPERIMENTS BY THE US FISH COMMISSION IN 1885. The partial completion, in August last, of the new laboratory building at the marine station of the Fish Commission, at Wood's Holl, Mass., with its convenient system of salt-water piping, permitted the necessary experiments being begun at that time with respect to the artificial hatching of lobsters--a branch of fish culture the great importance of which has long been felt in view of the rapid decrease in abundance of that valuable food product. Unfortunately the hatching season had then closed, but it was deemed advisable to ascertain the best methods of handling the eggs, in order that there might be as little delay as possible in starting operations next spring. Unlike most fishes, the lobster carries its eggs until they hatch. The eggs are fertilized while yet in the ovaries, and are soon afterward ex truded, but the length of the period of development is not known. As they issue from the body of the female, they are coated with a viscid substance that soon hardens into short, tough, and very flexible threads, by means of which they are attached in bunches or clusters, of variable sizes, to the swimmerets and undersurface of the abdomen or tail, the hinder feet, it is said, being used to aid in carrying them back and distributing them as they come from the apertures of the oviducts. The eggs are comparatively large (about one-twelfth of an inch in diameter) . and hardy, and each lobster carries from about 12,000 to 24,000, according to its size. The problem of lobster hatching on a practical scale is one that the Fish Commission has long had in view, but all of its marine laboratories up to the present time have been temporary structures, with insufficient accommodations and without the means of obtaining continuous suppliwa of water in suitable quantities. It was hoped that the new build- ing would be finished early enough in the spring to permit of the beginning of hatching work in June; but the hinderances which are inevitable to all such projects interfered to delay actual operations for another year. The hatching of small quantities of lobster eggs, as well as the eggs of other species of crustaceans, had. been successfully accomplished, from time to time, by members of the Fish Commission party interested in embryological studies, and the possibility of conducting hatching operations on a small scale, and of carrying the young through at least the first few stages of growth, needed no further proof; but the question of how to care for large masses of eggs, and especially for the young after hatching, was yet to be approached. -------------------------------------------------------------------------------------- BULLETIN OF THE UNITED STATES FISH COMMISSION. In the fall of 1884, soon after the inner fish basin at Wood's Holl had been completed, Capt. H. C. Chester, in charge of the station, transferred to it several hundred female lobsters with spawn, thinking that some of the eggs might hatch during the winter, but, if not, feeling certain that something might be done with them in the early spring. Unfortunately for his experiment, the work on the outer basins necessitating the employment of a large steam dredger, which kept the water constantly loaded with sediment, and the frequent blasting of rocks, caused the destruction of his entire stock before any results had been reached. The method of continuing the work in the summer had not yet been decided upon, when an opportune letter, received from the Norwegian fish-culturist, G. M. Dannevig, announced the successful hatching of lobster eggs of the European species, detached from the body of the parent, and the rearing of the young through the three earliest stages. The manner of conducting his experiments was not described, but the fact that he had accomplished good results with de tached eggs gave us a basis to work upon. His letter was as follows: FLODEVIG, near ARENDAL, NORWAY, July 14,1885.
The length of the young lobster soon after hatching is about 9mm. After 8 days, when the second changing of the shell or skin takes place, it has attained the length of 12mm, and after 16 days, when the third change occurs, it is about 16mm. The mortality was rather large for some days, but is now only 1 to 3 in 24 hours, so that 95 still remain out of 200 which were picked out for an experiment. They are very greedy, but not so bad in killing one another as they were in the beginning. I feed them principally with the soft parts of our crab. They like it well, but their slender legs sometimes get entangled in the soft mass, and then they die. Five hundred newly-hatched individuals are now in a separate apparatus for further experiments. I wish to find out at what stage the greatest loss takes place. I have great hopes now that I shall master this question during the season, so that I can proceed upon a large scale next summer. Very respectfully, G. M. DANNEVIG. --------------------------------------------------------------- Prof. SPENCER F. BAIRD,
* For a later account of this experiment, see letter of G. M. Dannevig, in Bull. U.S. Fish Commission, v, p. 446,1885. -------------------------------------------------------------------------------------- BULLETIN OF THE UNITED STATES FISH COMMISSION. 19 If a few eggs are cut from the swimmerets of a lobster and dropped into a jar of water, they will rapidly sink to the bottom, showing that their specific gravity is considerably greater than that of water. The knowledge of this fact led to the selection of the McDonald automatic hatching-jar, which has long been in use in shad propagation, for the first experiments, and a trial of about two months has demonstrated its superiority for this purpose over the other appliances that were tested. The principle on which the McDonald jar works has already been fully described,* and we need only mention here, for the purpose of showing its adaptability to the eggs in question, that the water entering through a long glass tube, reaching nearly to the bottom of the jar, causes an upward current of water through the jar, the force of which is regulated by the amount of inflow; the outlet is by means of a short tube passing only a little way into the upper part of the jar. The inlet tube is connected by rubber tubing with a supply pipe, and the outlet tube in the same manner with a waste pipe, and these connections being made, the movement of the eggs is entirely controlled by means of a stop-cock and the longer tube, the latter, by being raised or lowered, changing to a certain extent the force and character of the current. The flow is continuous and regular, and the jars need to be examined only occasionally, perhaps twice each day, for the purpose of forcing out the accumulation of sediment, as explained further on. The eggs are readily cut from the swimmerets and under surface of the lobster by means of small sharp scissors, the curved kind used in dissecting being especially well adapted to this purpose, although most any kind will answer. By taking ordinary precautions no harm is done to the parent, the small threads joining the eggs to the body having no organic connection with it. Most of the eggs come off in bunches of variable sizes, some containing two or three hundred, and others less, down to a very small number, but more or less of them become separated in the cutting, and in every batch there are many free eggs. This lack of uniformity in the composition of each lot of eggs is a source of great annoyance in handling them, the free eggs floating up more readily than the bunches and tending to escape through the outlet pipe, but it is not detrimental to the success of the work. In preparing the eggs, they were transferred as rapidly as detached to the hatching jars, previously filled with water, the eggs of each lobster being placed in a separate jar, as there is more or less variation in the specific gravity of the eggs of different individuals. As soon as each jar had received its allotment, the cap with its tubes was fastened on, and a connection made with the salt water supply pipe. The specific gravity of the eggs was not determined, but they require a relatively strong current of water to raise them above the bottom, the average amount allowed to pass through the jars having been nearly a gallon a minute for each. "Bull. U. 8. Fish Commiseion, iii, pp. 183-192,1883. -------------------------------------------------------------------------------------- 20 BULLETIN OF THE UNITED STATES FISH COMMISSION. The flow was so regulated as to give the larger bunches of eggs a gentle rotary-motion; but this caused the smaller bunches and the free eggs to rise sometimes to more than half the height of the jar and kept them quite strongly agitated. Although the eggs are very hardy, and in nature, while attached to the swimmerets of the parent lobster; are given but little motion, this greater activity appears to be essential to their well-being in the artificial hatching apparatus, for without it they soon die. Such a fate befell most of one lot contained in a McDonald jar, through which but a gentle current was allowed to pass, and in one of the hatching-boxes, where the supply of water was very much greater, though distributed over a much larger surface, so that no motion was given to the eggs, they all died inside of a week. The accumulation about the eggs of impurities from the water may have been the principal cause of this mortality,but as the eggs are well able to endure active motion and thrive best in a strong current, there can be no objection to pursuing that method. An illustration of the hardy character of the eggs is furnished by the fact that a small quantity left over night in a watch glass of sea water were alive and apparently in good condition in the morning, although the density of the water had been greatly increased by evaporation. The chief annoyances to hatching work at the Wood's Holl station this summer were, first, iron rust, and, second, sediment from the harbor. The supply mains in use when the laboratory was first opened consisted of iron pipes without a protective lining; they had been down a year, and gave off such a large quantity of rust, which often ap- peared as a dense reddish cloud of exceedingly fine suspended particles, that the hatching-jars would become strongly stained inside of a few hours and the eggs themselves become perceptibly coated. After the cement-lined pipes had been substituted, this trouble ceased for the most part, but a great deal of sediment was observed in the sea water the remainder of the season, and notwithstanding the strong current passing constantly through the jars, a very perceptible deposit was formed over the lower-lying eggs in the course of every twelve hours. The lighter particles of sediment also collected to a large extent on the sides of the jars and tubing, and often adhered to the more buoyant eggs. Cloth filters were used to strain out these impurities, but they proved unsatisfactory, and the course finally pursued was to force out the sediment every morning and evening by momentarily increasing the flow of water to its utmost capacity, and then shutting it off, repeating this operation at frequent intervals for several minutes. The effect was thoroughly to stir up the sediment, which, being lighter than the eggs, remained longer in suspension and was carried off when the flow was again made normal. The eggs were transferred to clean jars every four or five days, and the old jars thoroughly washed. By constant attention to all these details, the eggs were kept in a healthy and tolerably clean condition as long as the experiments were kept up. A neglect of these precautions always resulted in the BULLETIN OF THE UNITED, STATES FISH COMMISSION. PAGE 21 destruction of many eggs, although in the first lot of eggs prepared, which suffered greatly from iron rust, and was frequently left without care, sometimes for days at a time, until they were well covered with sediment, fully one-third were living at the end of eight weeks, when I left the Wood's Holl station. It does not seem practicable to keep the eggs of more than one lobster in each jar, as the eggs of different individuals differ more or less in specific gravity, and it is impossible to regulate the flow of water so as to give them all the required motion; but as the number is considerable in each, there is not sufficient excuse for attempting economy in that direction. The number of fertilized eggs carried by lobsters during the spawning season has been ascertained by careful computations in several cases, and varies from about 12,000 to 24,000, the latter number probably being rare. The most common number noticed during late years has been from 15,000 to 18,000. The question of the amount of motion to which the eggs should be subjected is one deserving much consideration. The females with eggs contained in the aquaria at Woods Holl remained very quiet most of the time, and the swimmerets and eggs were scarcely ever observed to be in motion. Confined within the narrow limits of an aquarium, with a strong light entering from all aides, it was not to be expected that their movements would be altogether natural. In nature, whether or not their swimmerets are kept moving regularly backwards and forwards, which is probably the case to a greater or less extent, the act of moving about in search of food or for change of ground must bring a constant change of water. With the Clark hatching-boxes, which are very successful for certain kinds of fish eggs, no good results were obtained, although the flow of water was much greater than in the McDonald jars. These boxes were tried in two ways, with a downward and an upward flow of water, but the eggs remained perfectly motionless, and at the end of a week were in such bad condition that they had to be thrown away. The experiments above described merely indicate a method by which lobster eggs detached from the parent may be successfully kept alive for a considerable length of time with sufficient economy to commend the process to future practice. Had the experiments been made during the hatching season, more satisfactory results would undoubtedly have been reached. It is not expected that in actuat practice the eggs will have to be kept very long in the jars. The extensive storage basins in front of the laboratory will afford accommodations for large quantities of "berried" females, which can be so arranged as to permit of their being readily examined from time to time and the condition of the eggs observed. As the eggs approach the last stages of development before hatching--a condition that is easily determined almost by the unaided eye--they can be transferred to the hatching jars, and the final changes allowed to take place under constant observation. -------------------------------------------------------------------------------------- PAGE 22 BULLETIN OF THE UNITED STATES FISH COMMISSION. As the hatching is limited to a period of about two months, it is probable that the eggs of many individuals reach maturity at about the same time, and a larg' number of jars can be manipulated together. The principal object in hatching the eggs in jars is to have the embryos under control immediately after hatching; but the best methods of caring for the young have yet to be decided upon, and furnish an interesting problem for investigation next spring. It is probable that the embryos cannot be kept in the McDonald jar, as they swim at the surface and would soon all escape through the outlet tube. They can, however, be transferred to large aquaria, to the large wooden tanks now rigged on the lower floor for the keeping of fish, or to floating cars in one of the basins. The last plan will probably answer best when working on a large scale, as the embryos will thereby obtain some food from the surrounding waters, while in both of the former cases food would have to be supplied them. A floating car suitable for the purpose has already been constructed, and now contains a number of berried lobsters, which it is proposed to keep over winter, if possible, in order to observe whether any hatching takes place during that season. This car is constructed on the plan of the ordinary fish cars, the openings being covered with a fine-mesh brass-wire cloth to prevent the escape of the young, but with the meshes large enough to permit of the entrance of such small life as the embryos would be likely to feed upon at the surface. The dimensions of this bar are 5 feet long, 3 feet wide, and 2 feet deep, but larger cars will be used if necessary. It is now moored in the outer basin, opposite one of the openings in the wall, where it receives the fall force of the current. A few McDonald jars will also be kept in operation, with lobster eggs, during the entire winter, for purposes of observation. It is not known how long the young can be kept in confinement, nor at what age it would be advisable to turn them over to the care of nature, but it will probably be possible to transport them alive to any other portion of the eastern coast, as the distances are nowhere great. NOTE. Since the above was written, a letter has been received from Capt. H. C. Chester, superintendent of the Wood's Holl station, giving an account of the hatching of a few lobster eggs in one of the McDonald jars early in November. The eggs were detached from the lobster and placed in the jar November 5; they began to hatch November 8, three days afterwards, and continued hatching for a few days longer, but only about 50 young ones were observed. The remainder of the eggs are still in the jar, in good condition. A few of the embryos were transferred to an aquarium with running water, and others to a small vessel in which there was no change of water. The former lived about 20 hours, the latter about 36 hours. The temperature of the water in the hatching jar November 5 was 54.3 Fahrenheit; on the 6th, 55; and on the 7th and 8th, 56 degrees. -------------------------------------------------------------------------------------- BULLETIN OF THE UNITED STATES FISH COMMISSION. 23 NECESSITY OF ATTEMPTING THE ARTIFICIAL PROPAGATION OF LOB- STERS. In a report to the U. S. Commissioner of Fish and Fisheries, on the lobster fishery of the United States, now in course of publication, the writer has given an account of what is known regarding the habits and abundance of both the American and European species, which differ but slightly from each other structurally. The investigations on which that report is based confirmed the fact, previously well known to those acquainted with the industry, that the abundance of lobsters, as well as their average size, has been rapidly decreasing from year to year on many portions of the coast, ever since the fishery has been vigorously pushed. A study of the habits of lobsters indicates that such a decrease is far more possible with that species than with the true fishes, which are, as a rule, more secure from the attacks of man. That a decrease has taken place, and that in some regions it has amounted to a serious loss, is attested by the statements of numerous fishermen and dealers, which are quoted at some length in the report above mentioned. All the States interested in the lobster fishery, excepting New Jersey, whose fishery is small, have enacted protective laws; but, either because these laws are inadequate or are not properly enforced, they have failed to stop the decrease, though they may have checked it more or less. As a result, the fishery is falling off in the United States, and we are even now dependent, to a greater or less extent, on the British Provinces for the supplies of our larger markets. The same trouble exists in Europe, where the lobster fishery is, of course, of much older date than in this country, and where it has been controlled by legislation for many years. Many elaborate reports have been published upon the European fishery by experts appointed to investigate its condition and needs, but they are apparently at as much loss there as we are here regarding the methods and benefits of protection. In Norway, which country possesses the most important European fishery, they have, as a last resort, sought relief through the aid of artificial lobster culture, and experiments to that end have been carried on for several years. In the United States, where the methods of fish culture are best understood and have been most productive of beneficial results, it is natural to suppose that the same course would have been often suggested, and such has really been the case, None of the trials up to this year have, however, been made according to the most approved methods of fish propagation, and insufficient means for carrying on any such practical experiments with respect to salt-water species of fish have alone prevented the Fish Commission from engaging in this work before. |