Larval biology of butterflyfishes (Pisces,Chaetodontidae): what do we really know?

Synopsis Relatively little is known of the pelagic portion of the life history of butterflyfishes. Eggs are small (<1 mm), pelagic and hatch in less than 30 hours. Most species pass through a so-called tholichthys larval interval characterized by elaborate, distinctive head spination:Coradion larvae have different head spination. While older chaetodontid larvae can be identified by adult characters, young (preflexion) larvae generally cannot now be identified below family. In tropical plankton studies chaetodontid larvae averaged <0.1% of larvae captured, and occurred in 13% of samples. This rarity is a major hindrance to further work, but is not unexpected in view of adult abundance. Larvae of a few taxa are most abundant in shelf waters, but larvae of many chaetodontid taxa seem to be most abundant in oceanic waters. In either case, waters near reefs have the fewest chaetodontid larvae. Offshore maxima of larvae appear to exist a few kilometers seaward of Great Barrier Reef ribbon reefs. Chaetodontid larvae may prefer the upper portion of the water column. Both size and age at settlement vary widely within the family and the large genusChaetodon, and the latter varies widely within species. Average size at settlement is less than 20 mm and age is less than 40 days. No correlation was found between size and age at settlement. Behaviour and feeding of chaetodontid larvae are essentially unstudied. Chaetodontid larvae seem to be least abundant in winter. The implications of these conclusions are discussed and some suggestions for further research are made. In all areas more work is needed.     

Simultaneous fine mapping of closely linked epistatic quantitative trait loci using combined linkage disequilibrium and linkage with a general pedigree

Causal mutations and their intra- and inter-locus interactions play a critical role in complex trait variation. It is often not easy to detect epistatic quantitative trait loci (QTL) due to complicated population structure requirements for detecting epistatic effects in linkage analysis studies and due to main effects often being hidden by interaction effects. Mapping their positions is even harder when they are closely linked. The data structure requirement may be overcome when information on linkage disequilibrium is used. We present an approach using a mixed linear model nested in an empirical Bayesian approach, which simultaneously takes into account additive, dominance and epistatic effects due to multiple QTL. The covariance structure used in the mixed linear model is based on combined linkage disequilibrium and linkage information. In a simulation study where there are complex epistatic interactions between QTL, it is possible to simultaneously map interacting QTL into a small region using the proposed approach. The estimated variance components are accurate and less biased with the proposed approach compared with traditional models.     

Colorimetric determination of cell numbers by Janus green staining.

A colorimetric assay using the basic azo dye Janus green has been developed to assess cell numbers in anchorage-dependent cell cultures, with special regard to the enumeration of osteoblastic cells. Therefore, cells are fixed in ethanol and stained with a 0.2% solution of Janus green for 3 min, followed by a destaining step of 1 min in tap water. The addition of diluted hydrochloric acid easily and immediately leads to dye elution from stained cell layers into the acidic supernatant which consequently is transferred into 96-well plates and read on a microplate reader at 595 nm. Working under standardized conditions, Janus green uptake in several cell lines is shown to be linearly correlated with cell numbers over a broad range of cell densities, in MC3T3-E1 cells from about 3% up to more than 300% of confluency. Absolute sensitivity of the assay allows detection of less than 1000 cells/cm(2). In comparison to many other colorimetric assays, the Janus green technique is simple to perform, fast, precise, stable, cheap, and well suited for processing large quantities of samples. Moreover, it is applicable to any culture formate and size, from irregular formed carriers up to 96-multiwell plates.     

Distributional ecology of milkfish,Chanos chanos,larvae in the Great Barrier Reef and Coral Sea near Lizard Island,Australia

Synopsis Plankton hauls captured 682 milkfish larvae (2.1–12.3 mm) in the Great Barrier Reef Lagoon and Coral Sea during 1979–1986. Larvae were present from November to March, and absent in April, July and October. We analyzed concentration, abundance and size-frequency data and concluded that spawning took place in the Coral Sea or at the outer edge of the continental shelf, apparently following an adult spawning migration of at least 50 km. Larvae then moved inshore to at least our most inshore routine sampling site near midshelf. Some larvae may have remained for a period in the lee of reefs along the shelf edge. Larvae apparently occupied the upper few metres of the water column, thereby becoming susceptible to shoreward movement in the wind-driven surface layer. Movement from spawning sites to midshelf probably required active maintenance of vertical position by larvae which enabled passive movement with favourable currents, and perhaps horizontal swimming. By the time larvae reach midshelf, continued inshore movement by horizontal swimming alone is possible.     

In situ settlement behaviour of damselfish (Pomacentridae) larvae

Settlement‐stage damselfish (Pomacentridae) larvae of 13 species in seven genera were obtained from light traps at Lizard Island, Great Barrier Reef, Australia. Behaviour, observed in situ by SCUBA divers, of 245 larvae (6–13 mm, L_S; 5–60 individuals per species) released individually within a few m of reefs during the day differed markedly among species. From 0–28% (range among 13 species) of individuals of each species swam away from the adjacent reefs without swimming to the reefs. Of those that swam to a reef, 0–75% settled. For three species, sufficient data were available to test the hypothesis that these percentages did not differ amongst reefs: the hypothesis was rejected in one species. From 0–75% of larvae that reached the reef were eaten, 0–63% subsequently left the reef and 0–60% were still swimming over the reef at the end of the observation period. Swimming speeds of all but one species were greater when swimming away from the reef than toward it. Most species exceeded average current speeds when swimming away from reefs, but not when swimming toward and over them. Average swimming depths were in the upper half of the water column for most species, and were somewhat greater where the water depths were greater. The time the larvae swam over the reef before settling and the distance swum varied greatly among species from 0 to a mean of 5.5 min and 43 m. Settlement habitats chosen differed amongst species, and in some species, they were very specific. Average settlement depth varied among species from 6–13.5 m. In one species, settlement depth varied between reefs. About half of the 53 observed interactions between larvae and reef resident fishes were predation attempts: fishes of eight species (six families) attacked larvae. The other interactions were aggressive approaches by 11 species of resident fishes, all but one of which were pomacentrids. Many of these aggressive interactions discouraged settlement attempts. Larvae of some species experienced no predatory or aggressive interactions, whereas in other species interactions averaged >0.6 per released larva. Species that swam more‐or‐less directly to settlement sites near the reef edge experienced more interactions. Even within the same family, settlement behaviour differed among species in nearly all measures.