Structure and function of the bulla, second maxillae and maxillary ducts of Salmincola californiensis (Dana, 1852) (Copepoda Lernaeopodidae)
Date
1977
Authors
Cousens, Norman Bruce Forrest
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Abstract
Structural details of the bulla, second maxillae, and maxillary duct system of adult female Salmincola californiensis (Copepoda: Lernaeopodidae) are considered in relation to their co-operative primary function of uptake of dissolved substances directly from the tissue fluids of the host, and some biological implications of this previously undescribed function are discussed. The mechanisms of haemal fluid circulation in S. californiensis are described briefly in relation to the maxillary uptake system. A technique is described for maintaining S. californiensis in vitro with the bulla isolated from the medium surrounding the body of the copepod, for periods of 14 to 21 days. Using this technique the relative permeability of the bulla, maxillary duct walls and external cuticle surfaces to a variety of types of dissolved substances was investigated. The external cuticle was found to be generally impermeable to most ionized readily water-soluble substances tested, including KMn04 in saturated solution, but permeable to some relatively small and weakly polar organic molecules of low water solubility. The maxillary ducts were found to be permeable to a variety of types of ions and polar molecules ranging in molecular weight up to at least 350 (including ionic vital stains, inorganic ions, some ¹⁴C-amino acids and ¹⁴C-glucose), but were relatively impermeable to un-ionized weakly polar organic molecules. Five potential chemotherapeutic agents (Ronnel, Trolene 20L, Ruelene, Ruelene 25E, and phenoxethol) were screened in vitro for toxicity to~- californiensis and those showing potential control ability were further tested in vivo on infected sockeye (Oncorhynchus nerka) smolts. A successful eradication procedure has not yet been developed as those compounds showing toxicity to Salmincola (Ruelene and phenoxethol) were more toxic to infected fish. However, a testing procedure is outlined and recommendations are made for future work of this nature. In addition, an hypothesis proposing a possible sequence of evolution and development of the bulla and maxillary duct system is presented and implications concerning the origin of family Lernaeopodidae are briefly discussed.