Michael H. Horn

Intertidal fishes : life in two worlds

K.L.M. Martin, M.A. Chotkowski, and M.H. Horn, Introduction. R.N. Gibson, Methods for Studying Intertidal Fishes. C.D. Zander, J. Nieder, and K.L.M. Martin, Vertical Distribution Patterns. K.L.M. Martin and C.R. Bridges, Respiration in Air and Water. D.H. Evans, J.B. Claiborne, and G.A. Kormanik, Osmoregulation, Acid-Base Regulation, and Nitrogen Excretion. R.N. Gibson, Movement and Homing in Intertidal Fishes. K. Kotrschal, Sensory Systems. E.E. DeMartini, Intertidal Spawning. R.M. Coleman, Parental Care in Intertidal Fishes. C.A. Pfister, Recruitment of Intertidal Fishes. M.H. Horn and F.P. Ojeda, Herbivory. S.F. Norton and A.E. Cook, Predation by Fishes in the Intertidal. R.N. Gibson and R.M. Yoshiyama, Intertidal Fish Communities. M.A. Chotkowski, D. G. Buth and K. Prochazka, Systematics of Intertidal Fishes. K. Prochazka, M. A. Chotkowski and D. B. Buth, Biogeography of Intertidal Fishes. M. H. Horn, Convergent Evolution and Community Convergence: Research Potential Using Intertidal Fishes. H.P. Schultze, The Fossil Record of the Intertidal Zone. Subject Index.

Activity of digestive enzymes in yolk-sac larvae of Atlantic halibut (Hippoglossus hippoglossus): indication of readiness for first feeding

The problem of determining when larvae should be offered food is particularly difficult in a species such as Atlantic halibut that has a long yolk-sac period (280–320 degree days, dd). In order to help determine at what age Atlantic halibut larvae are able to digest food, we compared the activities of key digestive enzymes in four yolk-sac stages at an age interval that has been recommended for initiation of feeding, i.e., 161–276 dd. We tested the hypothesis that digestive enzyme activities reach highest levels near the end of this age interval. Activities of trypsin, amylase, lipase and alkaline phosphatase were determined spectrophotometrically in whole yolk-sac larvae at 161, 179, 230, and 276 dd. The activities of the same enzymes were measured in metamorphic larvae (660 dd) and in their Artemia prey to provide reference levels from a fully developed digestive system and to estimate the importance of exogenous enzymes for Atlantic halibut larvae. Our results showed significant (P<0.001) differences in activities of all four digestive enzymes among the yolk-sac stages with a general pattern of increase from 161 to 276 dd. Trypsin activities reached their highest values at 230 dd, whereas those of lipase and alkaline phosphatase peaked at 276 dd. Amylase activities were detected only in the 230 and 276 dd stages, at statistically indistinguishable levels. Based on percentage comparisons, specific activities of trypsin and amylase in whole 276-dd larvae were only 12% and 2%, respectively, of those measured in the digestive system of metamorphic larvae, whereas specific activities of lipase and alkaline phosphatase in 276-dd larvae were more than 50% of those determined for metamorphic larvae. The calculated contribution of enzyme activities derived from Artemia prey to the relatively high levels of enzyme activity in the digestive system of metamorphic larvae was less than 10% for all enzymes except amylase, for which the contribution was estimated to be more than 50%. The results of this study support our hypothesis that the highest digestive enzyme activities in yolk-sac larvae are reached by 230–276 dd, i.e., near the end of the age interval recommended for first feeding. The observed pattern of enzyme activities suggests that feeding of Atlantic halibut larvae should be initiated after 230 dd, but not later than 276 dd to avoid the threat of starvation.

Digestive Enzyme Activities in Herbivorous and Carnivorous Prickleback Fishes (Teleostei: Stichaeidae): Ontogenetic, Dietary, and Phylogenetic Effects

We measured the activities of eight digestive enzymes in four species of herbivorous and carnivorous prickleback fishes and determined the effects of ontogeny, diet, and phylogeny on these enzyme activities. Of the four species, Cebidichthys violaceus and Xiphister mucosus shift to a more herbivorous diet as they grow (≥45 mm SL [standard length]), whereas Xiphister atropurpureus and Anoplarchus purpurescens remain carnivores throughout life. Digestive enzyme activities of small (30–40 mm SL) carnivorous juveniles were compared with those of larger (60–75 mm SL) wild‐caught juveniles that had consumed a natural diet and larger (60–75 mm SL) juveniles raised on a high‐protein animal diet. Cebidichthys violaceus and both species of Xiphister showed ontogenetic changes in digestive enzyme activities, whereas A. purpurescens did not. Despite dietary differences between X. atropurpureus and X. mucosus, these sister taxa displayed the most similar digestive enzyme activities from ontogenetic and dietary perspectives (high α‐amylase and lipase and low trypsin and aminopeptidase activities), and both were more similar to C. violaceus, a member of the same largely herbivorous clade, than either was to A. purpurescens, a member of an adjacent, carnivorous clade. The results support the hypothesis that phylogeny influences digestive enzyme activities in these fishes. Anoplarchus purpurescens, a carnivore with a diverse diet, showed great plasticity in enzyme activity, especially trypsin and aminopeptidase, which were elevated in this species to the highest level among the four species after consuming the high‐protein diet. These results support the hypothesis that fishes with relatively broad diets can modulate digestive enzyme activities in response to changes in dietary composition.

Abundance, diversity and seasonality of fishes in Colorado Lagoon, Alamitos Bay, California

Abstract A total of 152 169 fishes from 23 species were caught in monthly beach seine hauls during 1973 in Colorado Lagoon, the small, Y-shaped, upper arm of Alamitos Bay in southern California. Four species, northern anchovy, topsmelt, slough anchovy and shiner surfperch, comprised 99% of the catch. Numbers of species and individuals were highest during the summer (May–September) and both were highly correlated with lagoon temperature which ranged from 12·8–25·0 °C. Juveniles of northern anchovy were extremely abundant in August and September. Seven species were collected in only one month and six of these only in one of the warmer months (June–August). Five species, topsmelt, shiner surfperch, California killifish, staghorn sculpin and slough anchovy, occurred in wide size ranges and during most or all of the year and were considered to be residents. Three diversity indices (Shannon-Wiener, evenness and richness) reflected the changes that occur in numbers of species and individuals during the year.

Dietary selectivity in the field and food preferences in the laboratory for two herbivorous fishes (Cebidichthys violaceus and Xiphister mucosus) from a temperate intertidal zone

Diets and food selectivity of two stichaeid fishes (Cebidichthys violaceus and Xiphister mucosus) from the rocky intertidal zone of the central California coast (USA) were studied at each season of the year by gut content analysis and abundance measurements of potential macrophyte food items. Both fishes, after reaching a standard length of about 44 mm, were almost exclusively herbivorous. The bulk of the diet consisted of 8 to 10 species of chlorophytes and rhodophytes. These main dietary components were chiefly annual seaweeds with high surfaceto-weight ratios (sheetlike forms or small, highly branched forms). Perennial seaweeds were eaten in relatively large amounts only during the winter. Macrophytes eaten in only trace amounts included about 20 species of chlorophytes, chrysophytes, phaeophytes, rhodophytes and a spermatophyte. The small amount of animal material in the diet (never more than 2% by weight) could well have been ingested incidentally while the fishes were feeding on seaweeds. Food preference tests with up to 19 macrophyte species in the laboratory revealed that both fishes chose to eat three annual rhodophytes (Smithora naiadum, Porphyra perforata and Microcladia coulteri) in preference to Ulva lobata, an annual chlorophyte that was more abundant in the diets of field-caught specimens.

Evidence for dispersal of fig seeds by the fruit-eating characid fish Brycon guatemalensis Regan in a Costa Rican tropical rain forest

Abstract Studies were conducted at the La Selva Biological Station in the Atlantic lowlands of Costa Rica and in a greenhouse in California to assess the potential role of a Neotropical fish in dispersing the seeds of a rain forest tree. Feeding experiments showed that the seeds of Ficus glabrata H. B. K., a major, canopy-forming riparian tree, require approximately 18–36 h to pass through the digestive tract of Brycon guatemalensis Regan, an abundant riverine fish whose adult diet consists largely of leaves and fruits of this fig tree. The seeds were still viable after passing through the fish’s gut but germinated somewhat more slowly than seeds that had been left in the fig exposed to air or floated in water. Stem elongation of seedlings from seeds that had passed through the fish’s gut was faster than that of seeds in the other two treatments. Placement of seeds upstream may be more important than enhanced germination for plants such as Ficus that produce large numbers of seeds. Radio telemetry showed that five of six tagged fish had moved distances of 0.1–1 km upstream; seven other fish with transmitters, including three large males, were not relocated and may have moved into tributary streams for spawning or feeding. These findings suggest that Brycon can disperse large numbers of Ficus seeds and help maintain the upstream populations of the tree.

Fish guts as chemical reactors: a model of the alimentary canals of marine herbivorous fishes

The alimentary canals of marine herbivorous fishes are variously composed of a few basic structures strung together in series. We model the structures where digestive processes occur as chemical reactors following the model of Penry and Jumars: the stomach as a batch or continuous-flow stirred-tank (CSTR), the intestine as a plug-flow reactor (PFR), and the hindgut caecum as a CSTR. Other structures, where food is mechanically processed-gill rakers, pharyngeal mills, and muscular stomachs-are classified as gates. The optimality criterion for the model is the digestion of the most nutrient in the least amount of time. With the model we are able to predict gut configuration as a function of nutrient concentration and hypothesize that the guts of herbivorous fishes always have a PFR component and may or may not have a CSTR component. The Penry-Jumars model appears to provide a consistent theoretical framework for four main types of digestive mechanisms in marine herbivorous fishes and offers specific testable hypotheses on the feeding ecology and digestive physiology of four representative species of fish as well as other, still unstudied, herbivorous fishes.

Protein and Nitrogen Assimilation as a Factor in Predicting the Seasonal Macroalgal Diet of the Monkeyface Prickleback

Abstract The monkeyface prickleback Cebidichthys violaceus was fed monospecific diets of eight species of its preferred macroalgae each month (as available) for 1 year (May 1982-April 1983). Assimilation efficiencies were mostly above 70% for both protein and nitrogen despite considerable variation in these two constituents with respect to dietary species and season. Thus, the greatest amounts of protein and nitrogen are assimilated by this fish from algal species with the highest protein and nitrogen contents (the annual red algae Porphyra perforata, Microcladia coulteri, and Smithora naiadum). These are also the algae that have been shown to rank highest in laboratory preference experiments. Nevertheless, other species with lower protein and nitrogen contents are frequently more abundant in the diets of wild monkeyface pricklebacks. Additional factors, such as algal availability, must be considered in prediction of this fishs diet. Received December 7, 1983 Accepted April 8, 1984

Nutritional quality of macrophytes eaten and not eaten by two temperatezone herbivorous fishes: A multivariate comparison

The mean annual chemical compositions (ash, lipid, carbohydrate, protein, nitrogen and carbon) of 23 species of macrophytes (22 seaweeds and 1 seagrass) from a rocky intertidal habitat on the central California coast were determined from December 1981 through December 1982. These data were used to test the hypothesis that the 13 red and green seaweeds eaten by the two principal herbivorous fishes (Cebidichthys violaceus andXiphister mucosus) at the site are higher in nutritional quality than the 9 red and brown seaweeds and the seagrass not consumed by these fishes. A MANOVA using the ash, lipid, carbohydrate and nitrogen data showed that the centroids of the dietary and nondietary species groups were significantly different. In a two-group discriminant analysis that followed, only two species were misclassified as members of the opposite group. Multigroup discriminant analysis of the 23 macrophytes resulted in some overlap among dietary and nondietary species. Species were discriminated on the first canonical axis by ash content and on the second and third axes by lipid and carbohydrate contents. Nitrogen contributed little to the overall discrimination of species in the analysis. The nondietary red algaCorallina vancouveriensis, with its high ash content and therefore relatively low nutritional quality, was clearly separated from all other species in the analysis. Brown algae were of higher nutritional quality, but are not eaten by the two fishes, possibly because these seaweeds produce indigestible carbohydrates and secondary compounds. However, the exclusion from the diets of several red algal species that were virtually indistinguishable from the dietary red algae remains unexplained.

High tide movements of the temperate-zone herbivorous fish Cebidichthys violaceus (Girard) as determined by ultrasonic telemetry

Miniature, high-frequency (250 kHz), acoustic transmitters attached to the internal surface of the operculum were used to monitor the high tide movements of six medium-sized (225–410 mm SL) individuals of Cebidichthys violaceus (Girard) in the rocky intertidal zone near Piedras Biancas, California. The telemetry system consisted of a fixed, three-hydrophone array connected by cables to a shore-based receiver and microcomputer. Fish were tracked for sequences of 6 to 14 days, and the movements of as many as three individuals were monitored simultaneously. All fish showed a pattern of activity that was related primarily to the tidal cycle and secondarily to the diel cycle. Most movements of each fish occurred during flood tide. The three fish tracked in April were generally more active at night whereas the three tracked in June were more active during daylight hours. Differences in the time of flood tides with respect to the diel cycle may account for the dissimilarity in activity patterns of fish between the two months. Fish were highly restricted in their movements in that they were active < 1% of the time and traversed an area of ≈2 m2 or less per 40-min tracking episode. The results of this study coupled with known age and dietary attributes of the fish are consistent with the hypothesis that an energy-conserving lifestyle of low activity is the only one possible for a year-round, temperate-zone herbivore such as C. violaceus.