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Baby Fish of Lakes and Ponds INTRODUCTION Many different kinds of water babies abound in lakes and ponds. The minute and transparent babies of fishes are extremely difficult to find, see and study but surprisingly, no other vertebrate order has its babies occupying so many different habitats and displaying such widely diverse anatomical features. The fascinating early lives of fishes are slowly beginning to be revealed and it seems that those of marine fishes are even more unusual than those of freshwater fishes. Knowledge about the early lives of babies of fishes is widely scattered in the scientific literature. It is difficult to even see these early life stages because they are almost transparent at these minute sizes. Their blood is not red yet, so they are only coloured by their black eyes and by the black, gray or other colored chromatophore patterns which are produced by their DNAs and modified by the light conditions where they are living. Each species possesses a distinct and unique pattern of black, gray or other colored spots (chromatophores). It should be stressed that the babies of fishes do not ordinarily live in the same places as that of their adults; and they certainly do not resemble one another in anatomical or behavioural characteristics. Newly hatched fishes are rarely collected or examined close at hand. Until recently, professional fishery biologists did not know much about the early life of fishes; interest in early life history studies has risen exponentially during the last few decades. The publication rate of scientific studies in this field has risen from approximately ten titles per year around 1940 to more than fifty per year in the early 1970s. Why is the study of larval fish even of interest? The Federal Water Pollution Control Act amendments of 1972 in the United States caused a biological revolution. These amendments required heating plants, generating plants, and any other commercial endeavour using large volumes of water to monitor the young fish and other organisms passing through machinery by entrainment (straining water) methods. The species of fish and their numbers in any water body are closely related to water quality, so surveys of larval fish are a gauge of pollution. Experiments have shown that both eggs and larvae are more sensitive to the environment than adults; that is, they die quicker when pollution occurs. It has been demonstrated in laboratory studies that excess heavy metals and other pollutants cause spinal abnormalities, curved tails, abnormal development, and generally increased death among baby fish. It is well-known that fishes normally have good and bad years for hatching, so fishery biologists are continually trying to establish relationships between the abundance of eggs and larvae, and the annual success or failure of yearclasses or annual broods. It is important to know and understand the factors which cause unusual mortalities. And finally, scientific knowledge about the eggs and larvae of fishes can provide insight into our fragile natural resources while at the same time help to document our Canadian natural history heritage In the summer of 1958, I returned home from studying the planktonic animals living in Narragansett Bay, Rhode Island. I was extremely excited because I had just received a letter which offered me a grant to study the recruitment of walleyes (pickerel or doré jaune) in several small lakes in northern Wisconsin. After my experience in saltwater in Narragansett Bay, I had developed a theory that baby fish were living in the pelagic or limnetic regions of the small lakes that pockmarked glaciated countrysides. Could it be that baby walleyes and other fishes took up a life in the deep part of these small lakes? No one had described that phenonenon. Earlier, I had received permission to spend my first summer at the northern Wisconsin Biological Station where the famous pair, Edward A. Birge and Chauncey Juday, had spent the turn of the Century developing basic concepts of North American limnology. The Station consisted of five sleeping cabins and one large cabin which was used as a laboratory. I would work where "they" worked and would sleep where "they" slept. I felt honoured and thought this would be an opportunity of a lifetime ; I was not disappointed. During the following winter, I constructed a make-shift plankton net that could be towed from a small aluminum boat. I bought special Swiss silk bolting cloth which was normally used to sift fIour at flour mills. I bent a piece of round iron into a near-circle, welded it, and attached the plankton net to it with a small cord. The end of the large, conical-shaped net was tied off with a shoelace. Now I was ready to strain the tiny living organisms out of the lake water to find out if baby fish lived there. Somewhere I had read that baby fish could be more easily captured when it was dark than when it was light; something to do with dodging the net, I thought. So I prepared myself to work after sunset. Just being beside small isolated lakes at night with the moon reflecting upon their waters arouses exciting and romantic emotions within me. I put my boat and motor onto Little John Lake while mallards and black ducks scurried away to find other roosting sites. Ice had recently left the lake so the water was still cold to the touch. One could smell the strong aroma of fresh fish. I decided that this smell arose from the spawning activities of several species of fish which were in the midst of creating new lives along the shore. Every so often the sound of a jumping or rolling fish pierced the silent evening. I motored slowly out to the middle of the lake using moon to guide by. After stopping, I lowered my large homemade plankton net into the water by means of a pulley and a small nylon cord. I started up the motor, put it into first gear, and watched to see that the net was "fishing" correctly while still away from the propeller of the outboard motor. It was early spring and the water was crystal clear and free of algae that "dirtied" the water later in summer. I towed the net for five minutes just below the surface of the water, but those five minutes seemed like a lifetime. The anticipation was unbearable. Finally I stopped the motor, carefully lifted the end of the net into the boat, getting all wet in the process. I carefully untied the shoelace, and, low and behold, there were almost a hundred transparent baby fishes (they proved to be baby yellow perch). I had proved my theory that there were indeed deep water baby fishes living in small lakes. Scientific studies that arose directly or indirectly from that evening in the spring of 1959 include the following: Faber (1967, 1968), Werner (1969), Amundrud et al., (1974) and Storck et al. (1978). Baby fish can be collected with a variety of collecting devices such as hand dipnets, fine-mesh seines, plankton nets, light traps and slurp guns. These young vertebrate embryos are extremely delicate and must be handled with care. They can be collected and fixed with dilute formalin. Beer or wine works in an emergency! After fixing with a preservative, their tissues turn opaque and whitish; to observe them alive and transparent, they must be transferred quickly from the collecting device into a container with fresh water. Living baby fish are, of course, best obtained by collecting living eggs and hatching them in an aquarium. Light traps and slurp guns can also be used to collect live babies. Some eggs are collected easily by snorkeling over nests where male fish guard developing eggs. Baby fish can often be observed in shallow water while walking along shores of rivers or lakes or in deep water just below the surface while rowing or slowly motoring a boat. In order to see baby fish alive, one needs to be alert and observant for they are tiny and possess very little colour. However, after a little experience one can learn to recognize a number of species of larval fish even without taking them out of the water. The actual identification of baby fish is based upon various biological and environmental features: 1) body shape and other anatomical structures, 2) patterns of pigmentation, 3) countable structures (for example, finrays), 4) transient larval characters, and 5) environmental information, such as time of year, temperature of water, and habitat where they live, is also helpful. Persons identifying live specimens should be aware that live specimens show behavioural features in addition to anatomical features. Several things can be observed: whether or not they school together, whether they have dark, light or colored pigmentation, whether they swim at the surface or deeper in the water, how they swim (stiffly or wiggly), and whether they live in shallow beaver ponds, deep lakes, or rivers. When viewed alive and enlarged, baby fish are quite spectacular with their transparent tissues, organs and blood contrasted with their black eyes and black and brown pigment cells. Near Ottawa, Ontario, one can readily see the babies of sticklebacks, fathead minnows and redbelly dace in shallow beaver ponds (for example, the pond at Sarsaparilla Nature Trail or Mud Lake). The slow backwaters of the Ottawa River are good places to observe schools of golden shiners, white suckers and bullheads. A field study in nearby Devil Lake has demonstrated how young lake trout can be collected during active emergence from spawning gravels (Boraski and MacLean, 1981). This study was performed during the decade 1970 - 1980. Study of the identification of freshwater larval fishes in the Great Lakes region started on Lake Erie with an oceanographic-type survey. Marie Poland Fish completed this work (Fish, 1932) with her husband, Dr. Charles Fish, who at that time was Director of the Buffalo Museum of Science. Marie Poland Fish was both an artist and biologist, and many of her illustrations of baby fish are still valid today. A recent compilation of the literature on the early life of Great Lakes fishes was recently published (Auer, 1982) and takes over as the definitive guidebook of the Great Lakes from the famous study on Lake Erie. Part I. The Anatomy of Baby Fish in Lakes and Ponds Part II. Phenology of Baby Fish in Lakes and Ponds Part III. Shallowwater Species of Baby Fish in Lakes and Ponds Part IV. Deepwater Species of Baby Fish in Lakes and Ponds
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