A Guide to the Study of Fishes, Volume 2 (of 2) — Key Ideas to Explore

Ganoids and the Question of Natural Groups

Jordan devotes the opening chapters to ganoids, a group he treats with caution. He notes that some authorities question whether ganoids form a natural assemblage, and he presents evidence from both living and fossil forms. The Lepidosteus (garpike) receives special attention: its embryology and fossil record are discussed, and Jordan cites Gill’s argument for the group’s coherence. The writing here is methodical, listing families and orders—Lysopteri, Chondrostei, Selachostomi—with brief remarks on each. Jordan does not simply catalogue; he weighs characters such as fin structure and scale type, showing how classification rests on observable traits. The reader sees a scientist at work, testing hypotheses against specimens.

Salmon, Trout, and the Parent-Stream Theory

In the chapters on Salmonidæ, Jordan shifts from dry taxonomy to a more narrative style. He describes the Quinnat salmon’s life cycle and the “parent-stream theory”—the idea that salmon return to their natal rivers. The text includes practical details: the Jadgeska hatchery, salmon-packing methods. Jordan’s language becomes almost lyrical when discussing the Ayu, or sweetfish, and cormorant-fishing. Yet he never loses sight of structure: he distinguishes Coregonus (whitefish) from Salvelinus (charr) by fin-ray counts and tooth patterns. The section balances economic utility with biological curiosity, reflecting Jordan’s dual role as scientist and administrator.

Darters and Perches: Small Fish, Large Lessons

Jordan’s treatment of the Etheostominæ (darters) is among the most engaging in the volume. He notes that these small, bottom-dwelling fish are “the first to be disturbed by impurities in the water,” linking their ecology to water quality. He describes their feeding on dipteran larvae, their small size—Microperca punctulata barely reaches an inch and a half—and their absence in Europe, where similar niches are filled by Zingel and Aspro. The passage on the European perch (Perca fluviatilis) includes a quotation from Dr. Charles Conrad Abbott on habitat preferences, and Jordan contrasts American and European attitudes toward perch as a game fish. He even cites Thoreau’s remark that a boy counts perch as “real fishes.”

The Perch as a Type: Structure and Degeneration

Jordan uses the perch to illustrate a key evolutionary idea: that high specialization can be a step toward degradation. He explains that Cuvier placed the perch at the head of the fish series, but Jordan questions this based on vertebral count. Instead, he proposes the striped bass as a “fairer type.” The discussion of oral valves—a fold of connective tissue behind the premaxillary—shows Jordan’s attention to functional anatomy. He describes how these valves prevent water from flowing forward during respiration. This section exemplifies Jordan’s method: he takes a familiar fish, dissects its structure, and uses it to challenge received classification. The result is a text that teaches both facts and scientific reasoning.

Jordan’s volume rewards careful reading: his taxonomic decisions are never arbitrary, and his descriptions often carry ecological or evolutionary implications. Readers interested in the history of ichthyology will find a record of how early twentieth-century scientists classified fishes using external and internal characters. The book is best approached as a reference to be dipped into, not read straight through—each chapter stands alone, and the index helps locate specific families or species. Jordan’s voice, at once authoritative and curious, makes even the driest anatomical detail feel consequential.

Jordan’s patient counting of fin-rays took me back to my grandfather’s shelf, where I first met his old naturalist’s copy of The Harvest of the Sea A contribution to the natural and economic history of the British food fishes — Context and Discussion. Both books share that same quiet reverence for ordinary fish—herring, perch—as if their small scales held the whole ocean’s patience. I lingered there, thinking how taxonomy feels like love, one detail at a time.