Conservation, Ecology, and Management of Catfish: The Second International Symposium

<em>Abstract</em>.—We validated methods for estimating daily age of age-0 blue catfish <em>Ictalurus furcatus</em> and flathead catfish <em>Pylodictis olivaris</em>. Larvae of each species were reared in the laboratory and were sampled approximately every 10 d over a 4-month period. Five individuals of each species were randomly selected for daily age estimation from each of nine age-groups, ranging from 40 to 119 d posthatch for blue catfish and 20–121 d posthatch for flathead catfish. Mean daily ring count and known age were related for both species, indicating that daily ring deposition occurred in the otoliths of these fishes. Daily increment counts were accurate through 60 d posthatch for blue catfish and through 72 d posthatch for flathead catfish, with mean deviance of estimated age within 1 d of the known age. For both species, daily increments could be enumerated for older fish; however, accuracy decreased with age. We encourage researchers to utilize our aging technique to estimate hatch dates, the timing and frequency of hatching, and early growth rates of catfishes in wild populations. Such early life history information will be valuable in enhancing the management and conservation of important catfish populations.

Does eel metamorphosis cause a breakdown in the tenets of otolith applications? A case study using the speckled worm eel (Myrophis punctatus, Ophichthidae)

Several basic tenets of otolith research have been questioned recently with regard to eel metamorphosis. Specifically, some researchers have suggested that otolith increment formation is not daily, and otolith material may be resorped during metamorphosis. We conducted a rearing experiment to test the hypothesis that increment formation is daily and that the otolith continues to grow during eel metamorphosis. We marked the otoliths of wild-caught Myrophis punctatus leptocephali and reared these fish through metamorphosis. Metamorphosis was characterized by a decreasing standard length, pre-anal length, and body depth accompanied by an increase in pigmentation and a change in behavior. Increment formation was daily or near-daily through metamorphosis, and the otolith continued to grow during metamorphosis. Thus, the basic tenets of otolith application apply to eel metamorphosis, and non-daily ring deposition and resorption should not be used as explanations for otolith characteristics of eels (e.g., back-calculated hatch dates) unless demonstrated experimentally.

age and growth in a temperate euryhaline notothenioid, eleginops maclovinus from the falkland islands

falkland islands' mullet (eleginops maclovinus) were aged successfully using whole sagittal otoliths from 1403 individuals. marginal increment analysis indicated that one opaque and one translucent zone were laid down annually. unvalidated daily ring counts confirmed what was thought to be the first translucent zone. the translucent zones were found to form earlier in juveniles than in adults. juveniles over winter in the creeks and inlets whereas adults are more common in deeper inshore waters where there is a one month lag in the minimum winter water-temperature. the maximum observed age was found to be 11 years. the calculated von bertalanffy growth model (lt=124.41(1−e−0.14/year(t-0.01years))) showed that e. maclovinus is a fast-growing fish, growing on average 10.2 cm/year for the first six years of its life.

Daily Rings in Otoliths of Three Species of Lepomis and Tilapia mossambica

Daily rings formed on otoliths of known-age, laboratory-raised pumpkinseed (Lepomis gibbosus), green sunflsh (L. cyanellus), bluegill (L. macrochirus), and mozambique mouthbrooder (Tilapia mossambica) for at least 176, 170, 125, and 60 days, respectively. Subdaily rings found in young laboratory and wild fish were easily distinguished from daily rings. Width of daily rings on otoliths of green sunfish was linearly related to daily increase in length of fish, but the number of rings was a product of age of fish only, not length of fish or otolith radius. Growth and daily ring formation on otoliths in wild bluegill and largemouth bass (Micropterus salmoides) appeared to be similar to those in laboratory-raised fish. Otoliths of green sunfish held under simulated winter conditions ceased to produce daily rings, but did form an annulus. Two kinds of otolith tissue were present in most of the larger laboratory fish and wild bluegill but were not observed in wild largemouth bass. The first type, present in all areas of the otolith except the extreme posterior end, was translucent and had well-defined daily rings. The second type, present only in the posterior end, was opaque and had poorly etched daily rings that were difficult to discern. Both tissues were calcium carbonate in the aragonite form. Daily rings were found on otoliths offish held at constant temperature. Results of experiments with young mouthbrooders held under various light–dark and feeding cycles suggested that a 24-h light–dark cycle that entrained an internal, diurnal clock was required for daily ring production.