Parental behavior of intertidal fishes of the stichaeid genus Xiphister

Egg masses of Xiphister atropurpureus (Kittlitz) and X. mucosus (Girard) are tended by a single adult male wrapped closely around the mass. Males tend up to three egg masses at once. It is suggested that males only tend egg masses that they have fertilized. Comparison of egg numbers in spawned masses and in ovaries of gravid females, together with the observation of complete egg extrusion by spent females, demonstrates that each mass comprises the entire annual egg output of a female. Therefore, during a season a male may repeatedly spawn with different females.

Seasonal Shifts in the Spawning Site of a Northeast Pacific Intertidal Fish

In Barkley Sound, Vancouver Island, Canada, the spawning of the black prickleback, Xiphister atropurpureus, occurs during winter on rocky beaches protected from wave action. However, during spring, spawning occurs on rocky beaches of increasing exposure. This species spawns only under boulders with pebble, small rock, or shell substrates. Coincident reduction of wave action and increases in temperature probably cause the seasonal shift in the spawning site of this stichaeid.

The annual reproductive cycle of the black prickleback, Xiphister atropurpureus, a Pacific Coast blennioid fish

Semimonthly determinations of the gonad index made during the course of a year show that Xiphister atropurpureus has an annual reproductive cycle. The gonad index (ovary) increases during midwinter, attains a maximum value of 20 in late April–May, and declines to a base-line value of 0.5 from June to December. Spawning occurs during a 6-week period in late April–May. Spawning takes place in zone 4 of the intertidal habitat. Eggs deposited singly are fertilized and then shaped into a spherical mass by the parents. As egg envelopes harden, they adhere to one another to form a coherent mass. The egg mass is guarded by one or both parents. The annual reproductive cycle is considered to be a necessary consequence of the energetic demands of oogenesis combined with selection for a spawning period which is environmentally optimal. Alternative cycles based on modification of the present egg size (large)/egg number (few) relationship do not appear feasible, since the required modification of the egg size/egg number ratio would be selectively disadvantageous. The intertidal habitat of Xiphisier is subject to several potential environmental hazards: wave shock, reduced salinity due to rain and runoff, and excessively high or low temperatures. These are seasonal hazards which occur during winter or summer. Spawning is timed (April–May), so the probability that developing eggs will be exposed to environmental risks is minimized while the probability of exposure to environmental benefits is maximized. It is suggested that the reproductive cycle is under photoperiodic control.

The embryonic development of the black prickleback, Xiphister atropurpureus, a Pacific Coast blennioid fish

Spawning of Xiphister atropurpureus occurs during late April–May. Eggs are deposited in a coherent mass which is guarded by the parents. Development is divided into 35 stages. At 13 °C, eggs require 21 days to hatch. Stage 1 is an unfertilized ovum. Cleavage during stages 2–11 produces a typical teleost blastula. During epiboly, which begins at stage 12 and ends at stage 14, the embryonic axis is formed. Stages 15 to 31 are periods of embryonic growth and organ differentiation. Hatching occurs at stage 32. Larval growth occurs during stages 33–35. Yolk absorption is complete 10 days post hatching. The general pattern of development is similar to that of most teleosts. The newly hatched larva, although large, retains many embryonic characteristics. The eel-like shape of the adult is mirrored in the long body of the larva. Larval morphology and the life history of allied forms suggest a pelagic existence for Xiphister larvae. The behavioral pattern of egg aggregation during Xiphister spawning is considered to have a high survival value. (1) It reduces the probability of predation on single eggs and increases the probability of egg survival. (2) The inability of a predator to obtain positive reinforcement from finding single dispersed eggs may lead to abandonment of localized predator search patterns. (3) Since the egg mass is subject to a larger size, but numerically smaller predator class, the probability of egg-mass survival is increased. (4) As the unit of predation shifts from an egg to the egg mass, survival remains on an individual basis. Since the probability of predation is equally shared, the probability of survival appears to be increased by a factor proportional to total egg number (about 500). Parental care also enhances egg survival.

Sodium, Chloride and Water Balance of the Intertidal Teleost, Xiphister Atropurpureus

1. Studies were undertaken to determine the degree of regulation of sodium, chloride and water displayed by the intertidal teleost, Xiphister atropurpureus, over a range of salinities. 2. The plasma concentrations of sodium and chloride declined by approximately 15 % in 10 % sea water (48 mM-Na/kg.) and the intracellular and extracellular spaces increased by approximately 6 % in 10% sea water.

Sodium, Chloride and Water Balance of the Intertidal Teleost, Xiphister Atropurpureus

1. The rate of loss of sodium, chloride and water via the urine and the rate of intake of sodium, chloride and water by ingestion of the medium was determined for the euryhaline teleost, Xiphister atropurpureus. 2. The urinary losses of sodium and chloride were approximately 0.5 mM/kg. fish/day in both 100 % sea water (480 mM-Na/kg.) and 10% sea water. The ingestion of sodium and chloride by drinking the medium amounted to approximately 4 mM/kg. fish/day in 100% sea water and approximately 0.1 mM/kg. fish/day in 10% sea water. 3. The low rate of urine flow in 10 % sea water and the low drinking rate in 100 % sea water indicate a relative impermeability to water in both salinities.

Sodium, Chloride and Water Balance of the Intertidal Teleost, Xiphister Atropurpureus

1. The effluxes of 22Na, 36Cl and tritiated water from the euryhaline teleost, Xiphister atropurpureus were determined in 100 % sea water (480 mM-Na/kg.) and 10 % sea water. 2. Only the flux of sodium in 100% sea water contained an exchange diffusion component. The relative impermeability of Xiphister is shown by its low fluxes of sodium, chloride and water in both salinities. 3. In 10 % sea water the permeability to sodium declined while the permeability to chloride and water remained at sea water levels. 4. In both salinities diffusion and active transport are the major components of the sodium and chloride balance of Xiphister.